Biology test #3

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A heterozygous individual has___:

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A heterozygous individual has___:

two diff. Alleles of a gene

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An organism's observable traits constitute its___:

Phenotype

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10.2 Tracking traits:

  • 19th century

  • 1850

  • 19th century: people thought hereditary material was a fluid

    • Hypothesis: fluids from parents blended at fertilization

    • However, failed to explain seen patterns

  • 1850: Gregory Mendel began experiments breeding pea plants

    • Studied 30,000 plants over 10 years

    • Gained insight into nature of inheritance

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Mendel's Experiments:

  • what did he do?

  • what does it mean to breed true?

  • why did he use them plats that “breed true”

  • what did he conclude?

  • Controlled mating of plants

  1. Peas are self fertilizing (viable seeds form if a flowers pollen lands in its own carpel)

  2. Mendel removed the anthers to prevent self fertilization

  3. He cross fertilized flowers

  4. He planted resulting seeds

  5. Recorded traits

  • His experiments often began with plants that “ breed true” for particular traits

    • Breeding true: all offspring have same form of trait as parents, generation after generation

  • He cross fertilized plants that breed true for diff. Forms of a trait

  • Traits of offspring often appear in predictable patterns

  • He concluded that hereditary information passes in distinct units

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<p><strong>Inheritance in modern terms:</strong></p><ul><li><p>what are “hereditary units” ?</p></li><li><p>Diploid Cells</p></li><li><p>Homozygous</p></li><li><p>Heterozygous</p></li><li><p>Genotype</p></li><li><p>Phenotype</p></li></ul>

Inheritance in modern terms:

  • what are “hereditary units” ?

  • Diploid Cells

  • Homozygous

  • Heterozygous

  • Genotype

  • Phenotype

  • Mendel's “hereditary units” are genes

  • Individuals in a species share traits bc they have the same genes

  • Each gene occurs at a specific loco on a particular chromosome

  • Diploid cells have pairs of homologous chromosomes → they have two copies of each gene

  • Homozygous: having identical alleles of a gene on both homologous chromosomes

  • Heterozygous: having different alleles of a gene

  • Genotype: the particular set of alleles carried by an individual

  • Phenotype: an individual’s observable traits

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Dominant and recessive alleles:

  • what makes an allele dominant?

  • Phenotype depends on how products of alleles interact

  • Product of one allele influences the effect of the other

  • An allele is dominant when its effect masks that of a recessive allele paired with it

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T or F: all traits are inherited in a mendelian pattern:

False

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10.3 mendelian inheritance patterns:

  • Segregation of genes into gametes:

    • When homo during meiosis, the gene pairs on those chromosomes separate.

    • Alleles end up in separate gametes

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Segregation of genes into gametes

  • what is a Punnett square?

  • Plant homozygous for recessive allele (pp) can only make gametes that carry recessive allele (p)

  • A cress of the two homozygous plants (PPxpp) has only one outcome: gamete carrying allele P meets with gamete caring allele p

  • All offspring will be heterozygous (Pp)

  • Punnett square: diagram used to predict genotypic and phenotypic outcomes of a cross

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Monohybrid crosses:

:a cross between individuals that are identically heterozygous for alleles of one gene

  • Experiment begins with cross between individuals that breed true

  • Cross produces F1 hybrid offspring

  • Cross between two of these F1 individuals is monohybrid cross and produces F2 generation

  • The frequency at which two traits appear in the second generation provides information about dominance relationship between two alleles

  • Dominant trait will have a 3:1 phenotypic ratio

<p>:a cross between individuals that are identically heterozygous for alleles of one gene</p><ul><li><p>Experiment begins with cross between individuals that breed true</p></li><li><p>Cross produces F1 hybrid offspring</p></li><li><p>Cross between two of these F1 individuals is monohybrid cross and produces F2 generation</p></li><li><p>The frequency at which two traits appear in the second generation provides information about dominance relationship between two alleles</p></li><li><p>Dominant trait will have a <u>3:1 phenotypic ratio</u></p></li></ul>
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Dihybrid crosses

: a cross between two individuals that are heterozygous for alleles of two genes (AaBb, for ex)

  • Mendel's dihybrid crosses showed that hereditary units for s for different traits (alleles of different genes) often assort independently into gametes

  • 9:3:3:1 phenotype ratio

<p>: a cross between two individuals that are heterozygous for alleles of two genes (AaBb, for ex)</p><ul><li><p>Mendel&apos;s dihybrid crosses showed that hereditary units for s for different traits (alleles of different genes) often assort independently into gametes</p></li><li><p><u>9:3:3:1 phenotype ratio</u></p></li></ul>
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Independent assortment:

: A gene tends to be distributed independently of how other genes are distributed

  • When two genes on the same chromosome are far apart, crossing over occurs more frequently between them

  • They tend to assort independently

  • Two genes located close together on the same chromosome tend to be inherited together

<p>: A gene tends to be distributed independently of how other genes are distributed</p><ul><li><p>When two genes on the same chromosome are far apart, crossing over occurs more frequently between them</p></li><li><p>They tend to assort independently</p></li><li><p>Two genes located close together on the same chromosome tend to be inherited together</p></li></ul>
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One gene that gives rise to three traits is an example of___:

pleiotropy

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10.4 Non- mendelian inheritance:

  • Mendelian inheritance:

    • One gene gives rise to one trait

    • Alleles are either dominant or recessive

  • Non-mendelian inheritance:

    • Incomplete dominance

    • Codominance

    • Pleiotropy

    • Polygenic inheritance

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Incomplete dominance:

  • Condition in which one allele is not fully dominant over another, so the heterozygous phenotype is an intermediate blend between the two homozygous phenotypes

  • Example: snapdragon flower color

    • One allele encodes enzymes making red pigment

    • Another allele is mutated: enzyme cannot make pigment (flowers are white)

    • Heterozygous make only a little pigment, so flowers are pink

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Codominance:

: inheritance pattern in which two alleles are fully expressed in heterozygotes

  • IE: neither allele is dominant or recessive

  • Example: ABO blood type in humans

    • ABO gene encodes enzyme that modifies a carb on the surface of red blood cells

    • A & B alleles encode different enzymes, which modify the carbohydrate differently

    • O has a mutation that encodes a faulty enzyme – carbohydrate is unmodified

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Pleiotropy:

:A single gene affects multiple traits

  • Mutation in the genes product affect all the traits

  • Mutations in these genes are associated with complex genetic disorders

  • Example: sickle-cell anemia

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Polygenic Inheritance:

: pattern of inheritance in which multiple genes affect one trait

  • Hundreds of genes can be involved

  • Ex: Labrador colors

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A human example: Skin color

  • Variations in skin color depend on the kinds and amount of melanins produced

  • More than 350 gene products affect production and deposition of melanin and melanosomes ( organelles that make melanin )

  • Most people have the same # of melanosomes in cells, but they differ in size and shape of melanosomes, and kinds and amounts of melanin they make

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10.5 complex variation in traits

  • nature vs nurture

  • environment

  • Variation in traits begins w alleles, but the relationship between alleles and traits can be difficult to determine

  • Environment also influences form of many traits

  • “Nature vs Nurture”: is behavior based on genetics or the environment

  • Today we know that both genetics and environment affect phenotype

    • genotype + environment = phenotype

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Examples of environmental effects on phenotype:

  • Water fleas:

    • Low oxygen in water turns on expression of genes that produce hemoglobin, turning them red

  • Seasonal changes in coat color

  • Plant development

    • Changes in temp, night length and availability of water and nutrients trigger changes in gene expression

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Continuous variation:

  • what is it?

  • short tandem repeats

  • bell curve

: a range of small differences in forms of a trait

  • Often an outcome of polygenic inheritance, and genes with lots of alleles

  • Often associated with short tandem repeats: series of 206 nucleotides repeated many times in a row within regions of DNA

  • Ex: alleles with more short tandem repeats associated with longer dog faces

  • Bell curve: typically results from graphing frequency versus distribution for a trait that varies continuously

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Pedigree analysis is necessary when studying human inheritance patterns bc ___:

most of us choose our own mates and reproduce when we choose to

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10.6 Human genetic disorders:

  • Few easily observed human traits follow mendelian inheritance

  • Polygenic traits are common, and many phenotypes are influenced by both genetics and the environment

  • We decide when and who we mate with → makes studying inheritance patterns challenging

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Pedigrees

:charts illustrating phenotypes through gens. of a family tree

  • Used to study inheritance patterns in humans

  • Allows for a probability estimation of a phenotype reappearing in future gens

  • Shows whether a trait is associated w dominant or recessive alleles

  • Shows whether a trait is on an autosome or sex chromosome

Will ask to interpret a pedigree on the exam! → examples on slides

<p>:charts illustrating phenotypes through gens. of a family tree</p><ul><li><p>Used to study inheritance patterns in humans</p></li><li><p>Allows for a probability estimation of a phenotype reappearing in future gens</p></li><li><p>Shows whether a trait is associated w dominant or recessive alleles</p></li><li><p>Shows whether a trait is on an autosome or sex chromosome</p></li></ul><p></p><p>Will ask to interpret a pedigree on the exam! → examples on slides</p>
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Genetic disorders and abnormalities:

  • Genetic abnormality :

    • an uncommon version of a heritable trait that does not result in medical problems

      • Ex: polydactyly → extra fingers

  • Genetic disorder:

    • A heritable condition that results in a syndrome of mild or severe medical problems

      • Example: Cystic fibrosis

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10.7 Inheritance patterns in humans:

  • autosomal dominate trait

  • Human genetic disorders are characterized by chromosome of origin (sex or autosome) and whether it is recessive or dominant

  • Autosomal dominant trait: appears in homozygotes and heterozygotes

  • Inheritance clues:

    • Two affected parents can have unaffected offspring

    • Two unaffected parents cannot have affected offspring

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Examples of autosomal dominant disorders:

  • Achondroplasia: hereditary dwarfism, caused by mutation of gene for a growth factor receptor

    • Alles can be passed on to children

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The autosomal recessive pattern:

  • carriers

  • Autosomal recessive trait: appears in people homozygous for a recessive allele on an autosome

  • Carriers: heterozygous individuals who have the allele but not the trait

  • A child of two carriers has a 25% chance of inheriting allele from parents and developing the trait

  • Inheritance clues:

    • Two unaffected parents can produce affected child

    • Two affected parents only have affected offspring

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X linked recessive pattern:

  • : arise from genes on the X chromosome

  • Most x chromosome alleles are recessive

  • Inheritance clues:

    • An affected father never passes allele to a son - all children who inherit fathers X chromosome are female

  • Disorder appears more often in males than females - having one x chromosomes, a male must inherit only one allele to be affected by disorder; females must inherit two

  • If a mother has trait, all her sons also have it

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Nondisjunction at meiosis can result in ___:

aneuploidy

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T or F, An individual with three or more complete sets of chromosomes is polyploid:

True

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10.8 changes in chromosomes #:

  • polyploidy

  • aneuploidy

  • Polyploidy: having three or more of each type of chromosome characteristic of the species

    • Common in flowering plants (abt 70%)

    • Some insects, fishes, and other animals

    • Fatal in humans

  • Aneuploidy: having too many or too few copies of a particular chromosome

    • Usually bc of nondisjunction

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Nondisjunction:

  • trisomy

  • monosomy

: the failure of chromosomes to separate normally during meiosis or mitosis

  • In meiosis, creates gametes with abnormal number of chromosomes

  • If normal gamete (n) fuses with gamete that has an extra chromosome (n +1), the zygote will have three copies of that chromosome - trisomy

  • If normal gamete (n) fuses with gamete missing a chromosome (n -1), the zygote will have one copy of that chromosome - monosomy

<p>: the failure of chromosomes to separate normally during meiosis or mitosis</p><ul><li><p>In meiosis, creates gametes with abnormal number of chromosomes</p></li><li><p>If normal gamete (n) fuses with gamete that has an extra chromosome (n +1), the zygote will have three copies of that chromosome - trisomy</p></li><li><p>If normal gamete (n) fuses with gamete missing a chromosome (n -1), the zygote will have one copy of that chromosome - monosomy</p></li></ul>
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Down Syndrome:

  • A person born with 3 copies of chromosome 21 will have down syndrome (trisomy 21)

    • The only autosomal trisomy that allows humans to survive until adult hold

    • Affected individuals tend to have certain physical features

  • Nondisjunction leading to trisomy 21 increases with age of the mother

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Sex chromosomes aneuploidy

  • female abnormalities

  • male abnormalities

  • how many babies are born with an atypical # of sex chromies

don't need to know the names but should be able to recognize)

  • Abt 1 in 400 babies are born w an atypical # of sex chromosomes

  • Usually associated with learning difficulties, speech delays, and motor skill impairment

  • Female sex chromosomes abnormalities:

    • Turner syndrome (XO) - one X chromosome only

    • XXX syndrome

  • Male Sex chromosome abnormalities:

    • Klinefelter syndrome (XXY)

    • XXY syndrome

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Suppose a single nondisjunction event occurs during anaphase 2 of meiosis in a normal male cell from meiosis 2. Of the resulting sperm,___:

two would be normal, one would have an extra chromosome, and one would be missing a chromosome

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An X-linked carrier is a___:

heterozygous female

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10.9 genetic testing:

  • tests for newborns

  • tests for parents

  • prenatal tests

  • Risks??

  • Tests for newborns

    • Some disorders can be detected early enough to treat before symptoms develop

  • Tests for prospective parents

    • Probability of a future child inheriting a genetic disorder can be estimated by testing parents for specific alleles

  • Karyotypes & pedigrees are also useful

  • Prenatal tests:

    • Genetic screening is also done post-conception

    • Ultrasound imaging

      • Can reveal physical defects that may be the result of genetic disorders

      • Obstetric sonography - taken externally

      • Fetoscopy - taken inside uterus

    • Sampling fetal cells

      • Amniocentesis - small fluid sample taken from amniotic fluid

      • Chorionic villi sampling (CVS) - few cells removed from chorion (membrane surrounding amniotic sac)

  • Risk and intervention:

  • Invasive procedures carry risks to the fetus

    • Amniocentesis - no risk of miscarriage

    • CVS - 0.3% have underdeveloped or missing fingers and toes

    • Fetoscopy - increases risk of miscarriage from 2-10%

  • Couples at high risk of having child with genetic disorder may opt for reproductive interventions

  • In vitro fertilization: sperm and egg are mixed in a test tube

    • One of 8 cells removed from embryo at 48 hours

    • Genes analyzed

    • If no defects detected, embryo inserted into uterus

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Evolution is :

change in a line of decent

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12.1 reflections of a distant past:

  • Mass extinction occurred 66 mill years ago- wiped out dinos and 75% of all species

  • Event marked by worldwide rock layer, k-pg boundary

    • Rocks below layer: dinos, above layer: no dinos

    • Rich in iridium - rare on earth but common in asteroids

  • Giant crater found on yucatan peninsula

    • Formed by a 6-mile wide asteroid

    • Caused mass extinction

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12.2 Old beliefs, New discoveries:

  • the great chain of being

  • Abt 2,300 years ago, aristotle believed nature was a continuum of organization from lifeless matter Through plants and animals

  • His work influenced european scientists

  • In the 14th century, euros believed in “ the great chain of being”

  • “ the great chain of being” : Each link in the chain was a species and believed to have formed at the same time in one place in a perfect state everything that needed to exist already did

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New Evidence:

  • biogeography

  • comparative morphology

  • In 1800’s, euro scientists brought back tens of thousands of plants and animals from around the world

  • Each newly discovered species was cataloged

  • Began to see patterns in where species lived and similarities in body plans

  • Biogeography: the study of pattern in the geographical distribution of species and communities

  • Explorer alfred wallace believed shared traits might mean flightless birds share a common ancestor But was unsure how each landed on different continents.

  • Naturalists had trouble classifying organisms similar in some features but diff in others

    • Desert plants with similar structures can  have very different reproductive parts

  • Comparative morphology: study of anatomical patterns; similarities and differences among the body plans of organisms

  • If every species was created in a perfect state, why were there “useless” parts like wings on birds that do not fly, and the remnant of a tail in humans?

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New Ideas:

  • Discoveries in biogeography and comparative morphology began accumulating in the 19th cent

  • Evidence implied that Earth had changed over time, but this went against prevailing beliefs at the time

  • Arguments began among scientists to make sense of the new information

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New Ideas- Lamarckian Inheritance

  • In early 1800s, jean-baptiste lamarck (naturalist) had an idea that species gradually improved generation to generation due to a drive towards perfection

  • Believed environmental pressures produce change in an individual's body → resulting in change in their offspring

  • Lamarck’s understanding of inheritance was incomplete, but he was the first to propose a mechanism for evolution: change in a line of descent

  • A line of descent is also called a _______

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New Ideas: Catastrophism:

  • Georges Cuvier

  • Catastrophism

  • Georges cuvier: compare morphology expert

  • Rejected lamarck's ideas

  • Catastrophism: earth's landscape and been shaped by violent geologic events

  • Believed many animals went extinct during geologic events and new species were created following each event

  • Argued that the evidence for species changing did not exist

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New Ideas: uniformitarianism

  • who?

  • Charles lyell: geologist

  • Believed global catastrophe was not necessary to explain earth's landscape

  • Uniformitarianism: gradual, everyday geological processes shaped landscape

  • Geological processes that sculpt formations in the present could have sculpted rock formations in the past – if they took place over millions of years

  • This challenged prevailing belief of Earth being 1,000 years old, but most naturalists accepted Lyell’s idea

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Mary Anning:

  • Avid fossil hunter and discoverer of many important specimens

  • Corresponded with charles lyell and adam sedgwick, who taught charles darwin

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The process in which environmental pressures result in the differential survival and reproduction of individuals of a population is called___:

natural selection

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A trait is adaptive if it ___:

increases fitness

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12.3 Natural Selection:

  • Charles Darwin: (naturalist) was influenced by Lamarck, Culvier, and Lyell's findings

  • In 1831, darwin went on a 5 year expedition on the beagle

  • Found many unusual fossils, saw many diverse species

  • Upon return home (England), he studied his notes and fossils

  • Recognized that life changed over time, and thought about the forces that would cause that change

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Descent with modification:

  • Darwin fossils glyptodonts

  • Glyptodonts are extinct, but share many traits with today's armadillos

  • Armadillos live only where glyptodonts once lived

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Struggle with limited resources:

  • thomas malthus

  • what did darwin realize?

  • Darwin read an essay by Thomas Malthus: proposed disease, famine, and war limited the size of the human population

  • When people reproduce beyond capacity of environment, they run out of food and compete for resources

  • Only some survive the struggle for existence

  • Darwin realized wider application beyond humans

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Variation in traits:

  • What differences in traits distinguish closely related species from one another?

  • Finch species on isolated islands of galapagos

  • Finches had no opportunity to breed with those mainland populations

  • Galapagos finches resembled finch species on mainland, but had unique traits suited to their particular environments

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Fitness:

  • fitness

  • adaption

  • Darwin was familiar with variation in traits that selective breeding could produce

  • Darwin similarly reasoned that environments could “select” certain traits

  • Having a particular trait could give one species an advantage over other species

  • Individuals of a natural pop. vary in fitness

  • Fitness: the degree of adaptation to a specific environment

  • Adaption: trait that enhances fitness

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Natural selection:

  • Darwin realized that individuals best adapted to their environment were most likely to survive and leave more offspring than less fit rivals

  • Natural selection: differential survival and reproductive of individuals of a population based on differences in shared, heritable traits → need to be able to pick out this definition

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Great minds think alike:

  • alfred wallace

  • Darwin developed hypothesis of evolution by natural selection but did not publish his finds yet

    → kept collecting evidence for a decade

  • Alfred Wallace: was also writing Darwin at the time regarding patterns in geographic distribution

  • In 1858, hypothesis of evolution by natural selection was presented at a scientific meeting

  • Darwin published “On the origin of species”, with detailed evidence to support his hypothesis

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Phylogeny primer:

  • Phylogenies: show hypothesized relationships

    • Indicate common ancestors and shared lineages

    • Are built using homologous characters: characters that are similar due to a shared common ancestry

  • Can show evolutionary change in characters

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T or F Wrinkly textures in rock that formed from ancient biofilms living in marine sediments are fossils:

True

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The # of a species on an island usually depends on the size of the island and its distance to the mainland. This statement would likely be made by___:

a biogeographer

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12.4 fossil evidence:

  • Fossils: remains or traces of organisms that lived long ago

  • Most fossils include: mineralized bones, teeth, spores, shawls, and seeds

  • Trace fossils: footprints, nests, burrows, eggshells, feces - evidence of activities

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Fossilization:

  • It begins when an organism or traces become covered in sediment, mud, or ash

  • Overtime, groundwater seeps into the remains filling around and inside

  • Minerals dissolved in the water gradually replace minerals found in bone and other hard tissue (can crystalize inside cavities  to form detailed imprints of internal and external structures)

  • Extreme pressure turns the mineral to rock

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Sedimentary Rock

  • Most fossils are found in sedimentary rock

  • These rocks form as rivers, sand, volcanic ash, and other materials from land to sea

  • Mineral particles in the materials settle on seafloors in horizontal layers

  • After millions of years, the layers are buried and compacted into rock

  • Geologic processes can tilt sedimentary rock and lift it above sea level where erosion can leave it exposed

  • Deeper the layer, older the fossil

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The fossil record:

  • We have fossils for 250,000 know species

  • This is likely to be a small portion of past species:

    • Most remains are lilley not fossilized

    • Remains that escape scavenging may decompose in presence of moisture and oxygen

    • Fossils are often crushed or scattered by erosion

    • Many fossils are inaccessible

  • Many species can’t fossilize

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Finding a Missing Link :

  • Discovery of cetaceans (dolphins, whales) provide an example of how scientists reconstruct evolutionary history

  • Skeletons of modern cetaceans have remnants of pelvis and hind limbs (many years ago, they walked on land)

  • Modern cetaceans are related to artiodactyls (antelopes, sheep)

  • Cetaceans developed gigantic bodies for deep ocean swimming

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The time it takes for half of the atoms in a radioisotope sample to decay is called the ___. :

half life

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**Radiometric Dating: ****

  • Radioisotopes decay at a constant rate into daughter elements

  • Half life: the time it takes for half the atoms in a sample of a radioisotope to decay

  • Each radioisotope has a characteristic half life

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Dating a fossil: (know the concept)

  • radiometric dating

  • Age of fossils that still contain organic material can be aged via carbon isotopes

  • Almost all carbon on earth (and in organisms) is in form of 12C

  • Carbon 14 (14C) is a radioisotope, so it decays at a constant rate, and forms at a constant rate in atmosphere

  • Ratio of 14C to 12C in atmospheric CO2 is stable

  • Living things acquire carbon through their life in this ratio

  • When a living thing dies, it stops taking in Carbon and the ratio of 14C to 12C in its remains declines over time as 14C decays but 12 stays the same

  • This ratio of 14C to 12C in organism remains can be used to calculate how long ago it died

    • 14C half-life= 5,730 years

  • Radiometric dating: a method that can reveal the age of a material by measuring its isotope content

  • Carbon dating can only be used on biological material less than 60,000 years

  • Age of older fossils can be estimated by radiometric dating of volcanic rocks above and below the fossil

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Dating a Rock:

  • Original source of most rocks is magma →Lava

  • Lots of elements found in magma, including uranium → a radioactive element's → half life of  4.5 billion years

  • When magma cools, the uranium starts decaying into lead

  • Ratio of uranium to lead atoms can be measured to calculate how long ago the lava cooled

  • Oldest known rock = 4.4 billion years old

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The discovery of immense ridges and trenches stretching thousands of kilometers across the sea floor in the 1950s led to acceptance of the theory of___:

plate tectonics

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12.5 Changes in the history of Earth:

  • Many processes shape the earth's surface

  • All continents were once part of a supercontinent known as pangea that split into fragments and drifted apart aby 200 mil years ago

  • Continental drift explains why magnetic poles of gigantic rock formations point in different  directions in different continents

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Plate tectonics:

  • Continental drift was not immediately accepted as there was no known mechanism for continents to move

  • 1950s→ deeps sea explorers found huge ridges and trenches stretching thousands of kilometers, leading to a mechanism for continental drift

  • Plate tectonics theory : Earth’s outer layer of rock is cracked into huge plates, the slow movement  of which moves continents to new locations over geologic time

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Plate tectonics: fossil evidence:

  • Fossil record provides evidence in support of plate tectonics

  • Identical sequence of rock layers in south America, Africa, India, Antarctica, and Australia

  • Fossils from multiple species occur in these layers on multiple continents

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Supercontinents:

  • At least 5 formed and split up again, since about 4.55 billion years ago

  • One was named Gondwana (abt 540 million years ago); merged w/ another supercontinent to form pangea about 300 million years ago

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Tectonics and life's History:

  • Continents colliding brought together populations and species living on different landmasses and separated ocean species

  • Recycling between mantle and crust prevents elements crucial to life (carbon, nitrogen, phosphorus) from being permanently tied up in rocks

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The geologic time scale:

  • : chronology of earth's history

    • Correlates layers of rock with long time intervals

    • Composition of each layer hold info about environmental conditions, and fossils are recorded of life in the same period

  • Layers differ in composition and fossil content, which imply transitions in Earth’s history

  • Earth has been shaped by both gradual and catastrophic events

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Through ___, a body part of an ancestor is modified differently in different lines of descent.:

: divergent evolution

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12.6 evidence in form and function:

  • Species with closer evolutionary relationships have more traits in common

  • Comparative morphology provides evidence of such relationships in body form and function

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Homologous structures:

  • homologous: similar in position, structure, and evolutionary origin but not necessarily in function.

  • Descendants of a common ancestor may evolve in different ways depending on environmental pressures

  • Divergent evolution: the divergence of lineages descended from a common ancestor

    • Can give rise to homologous structures

  • Homologous structures: body parts that may appear different in different lineages but are derived from a common ancestral form

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Analogous structures:

  • convergent evolution

  • Structures that appear similar in different species are not always homologous

  • Convergent evolution: evolutionary pattern in which similar body parts evolve separately in different lineages

  • Convergent evolution can give rise to analogous structures: similar body parts that evolved  independently in different lineages

  • Wing surfaces:

    • Wings of insects, bats, and birds perform the same function, but adaptations differ

    • Bat and bird wings: limbs are homologous, but other structures that make them useful for flight are not

  • Plant forms:

    • Saguaro cactus (North America) and African milk barrel plant (Africa) have homologous and analogous structures

  • Homologous structure: accordion-like pleats in plant body swell when well watered, shrink as water is used

  • Analogous structure: cactus spines are modified leaves, while milk barrel spines are dried flower stalks

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T/F : Most mutations are adaptive:

False

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All of these data types can be evidence of shared ancestry except similarities in ___:

form due to convergent evolution

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12.7 molecular evidence for evolution:

  • Over generations, mutations change the DNA sequence of a lineage

  • Most mutations are neutral (no effect)

  • Mutations accumulate independently in genomes of separate lineages

  • The more recently two lineages diverges, the less there has been given mutations to rise

    • Similarities in nucleotide sequences of a shared gene, or in the amino acid sequence of a shared protein, are used as evidence of evolutionary relationships

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Comparing proteins

  • Evolutionary biologist often compare proteins sequence among species and use the number of amino acid differences to determine relatedness

  • Most mutations that affect phenotype are selected against

  • Occasionally, one is adaptive

  • Longer since divergence = more amino acid difference

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Comparing DNA

  • Recently diverged species may have many proteins with identical amino acid sequences

  • Even if the amino acid sequence is identical between species, the nucleotide sequence of the gene that encodes that protein may differ

  • Relative relatedness among species is measured by DNA similarities

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Similarities in development:

  • Generally the more closely related animals are, the more similar their development

  • Ex: all vertebrates go through a stage where the embryo has a tail and divisions called somites along the back

  • Many master regulator genes (genes that control cascades of gene expression) retain similar sequences and functions

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HOx Genes

  • : group of highly conserved master regulators

    • conserved= has remained essentially unchanged throughout evolution

  • Trigger formation of specific body parts

  • Insects have Hox gene called antennapedia that causes legs to form wherever it is expressed

  • Humans and other vertebrates have a version of this gene (Hoxc6 ) that causes ribs to develop in embryos

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___ is the OG source of new alleles.:

Mutation

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13.1 Farming superbugs:

  • Every time a cell divides, it is an opportunity for a mutation to occur

  • Intestinal bacteria  E. coli can divide every 17 minutes

    • Leads to rapid diversification

  • Human use of antibiotics is providing a selective pressure that results in E. coli and salmonella resistant to these antibiotics

  • Most common on farms where antibiotics are used in food animals

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13.2 Alleles in populations:

  • population

  • dimorphic

  • polymorphic

  • Population: a group of interbreeding individuals of the same species in the same area

  • Individuals in a pop. have the same genes, so they share certain features

    • Morphological traits (morpho = “form”)

    • Physiological traits such as details of metabolism

  • Sexual reproduction produces offspring with different allele combinations - almost every shared Trait varies among members

  • Trait with 2 distinct forms (two alleles) : dimorphic

  • Trait with three or more distinct forms (3 or more alleles): polymorphic

  • Most other traits are more complex (polygenic +   polymorphic + environment)

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Sources of variation in traits:

  • Mutation is the source of new alleles

  • Other events shuffle these alleles among offspring

  • Humans have more than 20,000 genes, all w/ multiple alleles

  • You are the only person who will ever have your particular combination of alleles

    • Except for identical twins!

<p></p><ul><li><p><u>Mutation is the source of new alleles</u></p></li><li><p>Other events <u>shuffle these alleles among offspring</u></p></li><li><p>Humans have more than 20,000 genes, all w/ multiple alleles</p></li><li><p>You are the only person who will ever have your particular combination of alleles</p><ul><li><p>Except for identical twins!</p></li></ul></li></ul><p></p>
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An evolutionary view of mutations:

  • how many new mutations is a child born with?

  • beneficial

  • neutral

  • harmful

  • Mutations are the raw material of evolution

  • Every human child is born with an average of 64 new mutations (64 DNA sequence variations that did not occur in the parents )

  • Beneficial mutation: improves the chance of survival or reproduction

    • Natural selection acts on these traits

    • Tend to be more popular in pop. over time

  • Neutral mutation: has no effect on survival or reproduction

    • Natural selection does not act on trait

  • Harmful mutation: reduces chance of surviving and reproducing

    • Tend to become less common in a population over time

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Allele Frequency:

  • gene pool

  • allele frequency

  • microevolution

  • evolution is not…

  • Gene pool: all the alleles of all the genes in a population

  • Allele frequency: abundance of a particular allele in a population's gene pool

    • Expressed in proportions:

      • if half the population is homozygous for an allele: frequency is 50%, or 0.5

      • If half the population is heterozygous for an allele: frequency is 25% or 0.25

  • Microevolution: change in allele frequency

    • Always occurring in natural populations, as natural selection and other processes that cause evolution are always in play

  • Evolution is not purposeful - there is no goal

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The observation that female lions prefer male lions with darker manes is an example of ___:

sexual selection

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13.3 Patterns of natural selection:

  • natural selection - one of several mechanisms by which microevolution occurs

  • Natural selection affects allele frequency in a population by operating on forms of a trait that vary in the population

  • Occurs in different patterns depending on species and selection pressures:

    • Directional selection

    • Stabilizing selection

    • Disruptive selection

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Directional selection:

: pattern of natural selection in which a form of a trait at one end of a range of variation is adaptive

  • Examples: warfarin resistance in rats, peppered moth color

<p>: pattern of natural selection in which a form of a trait at one end of a range of variation is adaptive</p><ul><li><p>Examples: warfarin resistance in rats, peppered moth color</p></li></ul>
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Directional selection: warfarin resistance in rats

  • Warfarin poisoning of rats began on the 1950s

    • Warfarin inhibits function of enzyme that regenerates vitamin k, a coenzyme producing blood clotting factors

  • By 1980, 10% of rats in urban areas were resistant to warfarin

    • Rats resistant to warfarin have mutation in gene that prevents warfarin binding

  • Exposure drives microevolution in rats

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Directional selection: color forms of the peppered moth

  • Peppered moths in england rest on trees during the day

  • In 1850, when air was clean and lichens grew on tree trucks, most peppered moths were light colored with black speckles; better camo than black ones

  • By 1900, black moths became much more common

    • Smoke from coal burning factories killed lichens on trees and trucks darkened with soot

    • Black moths were better camo from predatory birds

<ul><li><p>Peppered moths in england rest on trees during the day</p></li><li><p>In 1850, when air was clean and lichens grew on tree trucks, most peppered moths were light colored with black speckles; better camo than black ones</p></li><li><p>By 1900, black moths became much more common</p><ul><li><p>Smoke from coal burning factories killed lichens on trees and trucks darkened with soot</p></li><li><p>Black moths were better camo from predatory birds</p></li></ul></li></ul>
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Stabilizing selection:

: pattern of natural selection in which an intermediate form of a trait is adaptive, and extreme forms are selected against

  • Examples: body mass in populations of sociable weaver birds, human baby birth weight

<p></p><p>: pattern of natural selection in which an intermediate form of a trait is adaptive, and extreme forms are selected against</p><ul><li><p>Examples: body mass in populations of sociable weaver birds, human baby birth weight</p></li></ul>
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Stabilizing selection: sociable weaver

  • Stabilizing selection maintains an intermediate body mass in populations of sociable weaver bird

  • Trade off between risks of starvation and predation

    • Big birds less likely to starve then small

    • Big birds spend more time eating in open areas where vulnerable to predators, and are not as agile when escaping

  • Intermediate body size is adaptive trait in this environment

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