bio 2 - evolution ch 27 (post midterm)

do diploid organisms carry one or two copies of each chromosome(s)?

two copies of each chromosome, with one copy of each gene on each chromosome

Darwins ToE

• he first thought: specific hadn’t changed since the beginning of time - naturalistic

• then: proposed that species arise, change, and become extinct due to natural, not supernatural forces - evolve to survive natural selection

  • animals will die off if they do not change and only the best of an animal will survive

  • thinks over generations change occurs

Darwins natural selection

• individual organisms within a species exhibit variation that can be passed from one generation to the next - heritable variation

  • members of a population have different functional, physical, and behavioral traits

• organisms compete for available resources

• individual organisms within a population differ in terms of their reproductive success

  • ability to have more offspring = differential reproductive success

• organisms become adapted to conditions as the environment changes - says NS through differential reproductive success shapes traits, inherited from predecessors, in response to the environment - descent with modification leads to adaptation

Lamarck’s hypothesis about ToE

• inheritance of acquired characteristics - environment can bring about an inherited change

• thought that originally giraffes had short necks but stretched them to eat food high up and with continual stretching most giraffes now have long necks and over time passed their gradually longer necks to their offspring

epigenetic inheritance

chemical modifications to the DNA that occur in one generation may be passed on to later generations

Darwin’s natural selection

• organisms become adapted to conditions as the environment changes

• differential reproductive success shapes traits leading to descent with modification aka adaptation → evolved trait that helps an organism to be more suited to its environment

fossils

remains and traces of past life or any other direct evidence of past life

• shells, bones, and teeth are most often preserved

• most are embedded in sedimentary rock

• they are deposited in layers called strata

  • they are older than the one above it and younger than the one below it

fossils as transitional links

• shows intermediate between things such as dinosaurs and birds

  • whales adapted to increasing aquating lifestyle as seen as they have remnants of a hindlimb with fewer bones in smaller sizes and have changed nasal opening locations compared to their predicesors

the two methods for geological timescale

• relative dating method - determines relative order of fossils and strata but not actual date

• absolute method - radioactive dating technique to assign date based on half life of radioactive isotopes

evolution

all the changes that have occurred in living organisms due to differential reproductive success in living organisms over geological time

why do some individuals reproduce more than others?

because they are better suited to their environment

What are the fundamental characteristics all living organisms share?

• made of cells

• take chemicals and energy from environment

• respond to stimuli

• reproduce

biogeographical evidence of evolution

• changes in cells occuring in water → we are composed of 70-90% water

• continental drift - distribution of fossils and current species provide evidence of former positions of continents

mass extinctions

the main five have occurred at the end of:

• Ordovician

  • Continental drift of Gondwana to South Pole contributed

• Devonian

  • End of 70% of marine invertebrates

• Permian

• Triassic

• Cretaceous periods

  • due to meteorite striking Earth - dinosaurs went extinct

• a sixth is likely happening now

anatomical evidence of evolution

Common descent offers an explanation for anatomical similarities among organisms

• homologous structures

• vestigial structures

• embryological dev

homologous structures - anatomical evidence of evolution

Anatomically similar because they are inherited from a common ancestor

vestigial structures - anatomical evidence of evolution

Anatomical structures fully functional in one group and reduced or nonfunctional in another

• Example: snakes have no use for hindlimbs, and yet some have remnants of hindlimbs in pelvic girdle and leg

• occurs due to evolution and inheritance of anatomy from ancestors

embryological development - anatomical evidence of evolution

• At some time in development, all vertebrates have a tail and paired pharyngeal pouches → Reflects common ancestry

  • exception is analogous structures ie Serve the same function but not constructed similarly and do not share a common ancestry - wings of bird or wings of insect

biochemical evidence of evolution

• Almost all organisms use the same basic biochemical molecules, including DNA, ATP, and many enzymes

• all have the same DNA triplet code for same 20 amino acids in their proteins

• diversity is only due to slight differences in genes

artificial selection - humans as agents of evolution

human-controlled breeding to increase the frequency of desired traits

•Works like natural selection

•Original population exhibits various characteristics, allowing humans to select preferred traits

microevolution

is the change in allele frequencies in a population over time

• includes population genetics

population genetics in microevolution

is the field of biology that studies the diversity of populations at the level of the gene - interested in how genetic diversity in populations changes over generations

gene pool

the sum total of all alleles of all genes in individuals in a population

• if there were 50 alleles in the peppered moth ___ (2 alleles x 25 moths) 10 were D and 40 were d then the frequency of D and d alleles would be 10/50 and 40/50

allele frequency

the proportion of each allele in a population’s gene pool

• D and d adds up to 1

  • This relationship is true of the sum of allele frequencies in a population for any gene of any diploid organism

  • P + Q = 1

Hardy Weinberg equilibrium

describes a population in which allele frequencies do not change over time. uses equation p² + 2pq + q² to describe the genotype and allele frequencies in a population

• principle says: Allele frequencies in a gene pool will remain at equilibrium/constant, in each generation of a large, sexually reproducing population as long as the following five conditions are met

• all five conditions are never met in real world yet populations are constantly evolving

• the principle is an important tool because the violation of one or more of the conditions causes allele and genotype frequencies to change in predictable ways

what are the five conditions that must be met for the Hardy-Weinberg equilibrium

• No mutations

• No genetic drift

• No gene flow

• Random mating

• No selection

yet all five conditions are never met in real world yet populations are constantly evolving

are changes in traits that occur over an individuals lifetime evidence they have evolved?

no! these traits are not heritable

• in order for traits to evolve they must be passed on to subsequent generations

• evolution is about change in a heritable trait within a population, not within an individual, over many generations

significant extinction events occurred between:

holocene approx 11k years ago and now which is anthropocene

the mass extinction of 50% of all species, dinosaurs, and most reptiles occured:

between the mesozoic and current cenozoic era between 66 million years ago to 55.8 million years ago

the mass extinction of 48% of all species, including corals and ferns occurred:

between periods of mesozoic - triassic and jurassic - 201 to 145 million years ago

the mass extinction of 83% of species on land and sea occurred:

between paleozoic and mesozoic periods permian and traissic 252 to 201 million years ago

the mass extinction of over 50% of coastal marine species and corals occurred:

during the paleozoic periods of devonian 360 to carboniferous 299 million years ago

the mass extinction of over 57% of marine species occurred:

during the paleozoic periods of ordovician 443 to silurian 416 million years ago

when did Earth form?

4570 million years ago

When did the first prokaryotic cells evolve?

3500 million years ago

When did the first eukaryotic cells evolve?

2100 million years ago

When did the first protists diversify?

1000 years ago

absolute dating method

way of assigning actual date of a fossil by using the half life - length of time it takes for half of the radioactive isotope to change into another stable element

when did the five major mass extinctions occur?

during the end of ordovician (continental drift), devonian, permian, triassic, and cretaceous (asteriod) periods

what do population geneticists study?

microevolution by measuring the diversity of a population in terms of allele and genotype frequencies over generations

genetic drift - condition that must be met based on Hardy Weinberg equilibrium

random changes in allele frequencies by chance. If a population is very large, changes in allele frequencies due to chance alone are insignificant

• deviation will lead to loss of allele diversity and some may disappear - change in allele frequency means evolution

no gene flow - condition that must be met based on Hardy Weinberg equilibrium

gene flow is the sharing of alleles between two populations through interbreeding. if there is no gene flow then migration of individuals and therefore their genes into or out of the populations does not occur

• deviation will lead to individuals carrying alleles into or out of the population - change in allele frequency means evolution

random mating - condition that must be met based on Hardy Weinberg equilibrium

random mating occurs when individuals pair by chance and not according to their genotypes or phenotypes

• deviation will change genotype frequencies but will not lead to evolution

no selection - condition that must be met based on Hardy Weinberg equilibrium

often the environment selects certain phenotypes to reproduce and have more offspring than other phenotypes. if selection does not occur no phenotype is favored over another to reproduce

• deviation will have certain alleles selected for or against and change the alelle frequencies leading to evolution

bottleneck effect of genetic drift

results in severe reduction in the gene pool that affect allele frequencies after a disaster

founder effect of genetic drift

when a few individuals form a new colony and only a fraction of the total genetic diversity of the original gene pool is represented in these individuals

• particular alleles carried by the founders are dictated by chance alone

• results in severe reduction in the gene pool that affect allele frequencies

evolution by natural selection requirements:

• individual variation - members of a population differ from one another

• inheritance - many of the differences are heritable genetic differences

• overproduction - too much breading for what the environment can support

• differential reproductive success - some people are better at producing and producing fertile offspring

what is fitness in biology

measured by the number of fertile offspring produced htroughout its lifetime

what are the main three types of natural selection?

stabilizing selection, directional selection, and disruptive selection

stabilizing selection

extreme phenotypes are selected against and individuals near the average are favored

• can improve adaptation of the population to those aspects of the environment that remain constant

  • birth weight → babies have a better chance of survival when intermediate weight over too ig or too small

directional selection

occurs when an extreme phenotype is favored and the distribution curve shifts in that direction

• changes average phenotype in a population - can occur when adapting to a changing environment

  • ie bacteria that becomes resistant to antibiotics to survive

disruptive selection

two or more extreme phenotypes are favored over any intermediate phenotype

• in certain areas thrushes feed on snails with dark shells and in other areas on snails with light banded shells so they have changed to survive in their respective habitats

how an variation be maintained despite forces trying to reduce it?

1. mutations still generate new alleles

2. recombination and independent assortment shuffle alleles during gametogenesis

3. fertilization creates new combinations of alleles to those in the gene pool

4. gene flow might still occur

5. natural selection favors certain phenotypes but the other types may still remain in reduced frequency

the heterozygote advantage

only alleles that are expressed are subject to natural selection and this can help protect recessive alleles that otherwise could be weeded out of the gene pool by natural selection

• balanced polymorphism : when NS favors a ratio of two or more phenotypes in generation after generation → sickle cell disease

• recesisve phenotype may have greater fitness in a changing environment

what are the species concepts?

morphological, evolutionary, phylogenetic, and biological

morphological species concept

species are distinguished from each other by one or more diagnostic traits or distinct physical characteristics

• disadvantages: in some animals it is hard to see measurable traits (bacteria), some organisms seem to be identical, some have subtle and sometimes misleading differences, fossils do not tell you about the color behavior or anatomy of soft tissue

evolutionary species concept

relies on identification of certain morphological traits to distinguish one species from another

• requires that the members of a species share an evolutionary pathway

• small changes that seem to be transitions in the same evolutionary would mean changes in a trait would now allow for a new species to be conceived but abrupt changes indicate the evolution of a new species in the fossil record

phylogenetic species concept

an evolutionary family tree is used to identify species based on a common ancestor, a single ancestor for two or more different groups

• a species is the smallest set of interbreeding organisms, usually a population, that shares a common ancestor

• a phylogeny, a branch that has all descendents of a common ancestor is said to be monophyletic - main criterion for defining species

• advantage is not relying on morphological traits to define a species

biological species concept

relies on reproductive isolation, or the physiological, behavioral, and genetic processes that inhibit interbreeding

• if organisms cannot pate and produce offspring in nature or if their offspring are sterile they are defined as different species

reproductive isolation mechanism

accomplished by isolating mechanisms

• prezygotic isolating mechanisms are in place before fertilization and thus reproduction is never attempted

• postzygotic isolating mechanisms are in place after fertilization so reproduction may take place but does not produce fertile offspring

speciation

occurrs when one species gives rise to two which continue on their own evolutionary pathway

• whenever reproductive isolation develops between two formerly interbreeding groups or populations

• ie allopatric speciation or sympatric speciation

allopatric speciation

occurs when populations become separated by a geographic barrier and gene flow is no longer possible

sympatric speciation

when a single population divides into two reproductively isolated groups without being geographically isolated

• found with plants where multiplication of the chromosome number in one plant prevents it from successfully reproducing with others of its kinds - can self reproduce to maintain this new plant species

adaptive radiation

the proliferation of a species by adaptation to different ways of life

• Tree finches are similar to woodpeckers but lack the long tongue so they use a cactus spine or twig to ferret out insects

pace of speciation

two hypotheses about the pace of speciation and therefore evolution

1. phyletic gradualism model

2. punctuated equilibrium model

phyletic gradualism model - pace of speciation

supported by Darwin - states change is slow but steady within a lineage before and after a divergence (splitting of the line of descent)

• Not surprising there are few transitional links because new species come after reproductive isolation which cannot be detected in fossil records

• only when a new species evolves and displaces the existing species is the new species likely to show up in the fossil record

punctuated equilibrium model - pace of speciation

says that long period s of stasis (no visible change) are followed by rapid periods of speciation

• uses fossils to show that speciation occurs relatively rapidly and can explain why there are few transitional links

• mass extinctions are usually followed by rapid periods of speciation

systematic biology

the study of evolutionary history of biodiversity

• uses characteristics of living and fossil organisms to infer the evolutionary relationships among organisms and to then organize biodiversity based upon these relationships

taxonomists

scientists that study taxonomy, use several categories of classification created by Carl Linnaeus to show varying levels of similarity

• the higher the category the more inclusive it is

taxonomy

the branch of systematic biology concerned with identifying, naming, and classifying organisms

taxon

a general name for organisms that exhibit a set of shared traits

• bionomial system of nomenclature is used to assign a two part name (genus and species)

  • second part of the name tells you something about the organism ie sapien refers to a large brain

classification

process of naming and assigning organisms or groups of organisms to a taxon

phylogeny

a hypothesis of evolutionary relatedness among taxa represented by a family tree - the estimation and visual representation of history

cladistics

a method phylogeneticists use to construct a phylogeny called a cladogram

• branches on the cladogram = clades and each has the most recent common ancestor and all its descendents

• only traits that are shared among all individuals are used to define a clad - shared derived traits

  • not found in the “outgroup”

• cladistics are based on parsimony - which considers the simplies explanation (least changes) is best to hypothesize evolutionary history

convergent evolution

independent evolution of analogous traits in distantly related lines of descent

• analogous structures have the same function in different groups but organisms with these structures do not share a recent common ancestor → instead it is due to adaptation to similar environments

Linnaean classification system

carries historical taxa but sometimes homologous not analogous traits were used to classify organisms which then has trouble

three domain system

method of classification with two prokaryote groups (bacteria and archaea) and the eukaryote domain (eukarya)

supergroup

The classification of protists is complex; involves an additional level of classification so it now has this above kingdom but below domain