Biology test #3

A heterozygous individual has___:

A heterozygous individual has___:

two diff. Alleles of a gene

An organism's observable traits constitute its___:

Phenotype

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

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

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

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

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

False

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

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

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

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

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

One gene that gives rise to three traits is an example of___:

pleiotropy

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

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

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

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

Polygenic Inheritance:

: pattern of inheritance in which multiple genes affect one trait

• Hundreds of genes can be involved

• Ex: Labrador colors

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

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

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

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

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

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

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

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

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

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

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

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

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

Nondisjunction at meiosis can result in ___:

aneuploidy

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

True

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

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

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

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

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

An X-linked carrier is a___:

heterozygous female

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

Evolution is :

change in a line of decent

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

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

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?

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

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 _______

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

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

Mary Anning:

• Avid fossil hunter and discoverer of many important specimens

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

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

natural selection

A trait is adaptive if it ___:

increases fitness

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

Descent with modification:

• Darwin fossils glyptodonts

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

• Armadillos live only where glyptodonts once lived

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

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

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

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

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

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

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

True

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

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

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

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

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

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

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

half life

**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

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

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

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

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

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

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

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

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

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

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

: divergent evolution

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

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

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

T/F : Most mutations are adaptive:

False

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

form due to convergent evolution

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

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

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

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

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

___ is the OG source of new alleles.:

Mutation

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

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)

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!

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

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

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

sexual selection

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

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

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

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

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

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