summer - bio 190 - ch 19

19.1

overview of evolution

evolution

a change in one or more heritable characteristics of a population from one generation to the next

natural selection

environment

artificial selection

human hand

Darwin

influenced by work in other fields and his own observations on the Beagle (his boat) during about 5-year journey

Darwin noted distinctive traits of island species that

allowed them to better exploit their environment

darwin suggets

that existing species are derived from pre-existing species

Darwin expressed his ideas about evolution as

“the theory of descent with modification through variation and natural selection “

variation

traits heritable - passed from parent to offspring

genetic basis was not yet known in Darwin’s time

natural selection

more offspring are produced than can survive

competition for limited resources

Individuals with beneficial heritable traits are more likely to survive and reproduce

as a result of natural selection,

certain traits that facor reproductive success become more prevalent in a population over time

19.2

evidence of evolutionary change

selective breeding

the english bulldog

dogs

convergent evolution

similar DNA because of a similar habitat

2 species from different lineages have independently evolved similar

analogous structures

Fossils show

evolutionary change

transitional form

biogeography

The study of the geographic distribution of extinct and living species

homology

refers to a similarity that occurs due to descent from a common ancestor

may involve anatomical, developmental, or molecular features

vestigial structures

anatomical features that have no current function but resemble structures of presumed ancestors

developmental homology

refers to similarities that occur during development

molecular homology

refers to similarities that occur at the molecular level

The degree of similarity between genetic sequences from different species reflects the evolutionary relatedness of those species

19.3

genes in populations

gene pool

includes all of the alleles for every gene in a population

polymorphism

refers to the presence of two or more alleles at a gene locus for a given character within a population

ex. two color variations

the DNA difference between alleles

large healthy populations exhibit

high levels of genetic diversity

every animal, human have __ alleles out of __

2

4

how can genes become polymorphic?

deletion, duplication, or change in a single nucleotide

single-nucleotide polymorphism SNP

The smallest type of genetic variation that can occur within a gene and is the most common

population

a group of individuals of the same species that occupy the same environment at the same time and can interbreed with one another and produce viable offspring

genetic variation

can be analyzed quantitatively

Calculations of allele frequency and genotype frequency are fundamental when analyzing populations

allele frequency =

number of copies of a specific allele in a population / total number of all alleles for that gene in the population

genotype frequency =

number of individuals with a particular genotype in a population / total number of imdividuals in the population

genotype frequency

calculated from observational data of phenotypes in a population

allele frequencies

calculated from known genotype data

hardy-weinberg equation

describes the relationship between allele and genotype frequencies when a population is not evolving

fundamental principle in population genetics

allows pop gens to determine the baseline allele frequencies in a population

hardy-weinberg law

1. calculate the dominant allele frequency

slides 33-34

hardy-weinberg equation describes the relationship between

allele and genotype frequencies when a population is not evolving

p + q = 1

and

p² + 2pq + q² = 1

if they do, the population is not evolving → stable

if they don’t, pop is evolving, figure out why?

equilibrium =

population NOT evolving

no new mutations

populations is so large allele frequencies do not change

no migration

no random mating

in reality, populations rarely reach equilibrium

if frequencies are not in equilibrium, an evolutionary mechanism is a work

microevolution

used to describe changes in a population‘s gene pool

(such as changes in allele frequencies)

from generation to generation

genetic drift

random chance

“accident“

19.4

natural selection

over time, natural selection may result in

adaptations

changes in populations of living organisms that increase their ability to survive and reproduce in a particular environment

as a result of natural selection

certain traits that favor reproductive success become more prevalent in a population over time

reproductive success

the likelihood of an individual contributing fertile offspring to the next generation

fitness (w)

The relative likelihood that one genotype will contribute to the gene pool of the next generation compared with other genotypes

Fitness is a measure of reproductive success

directional selection

individuals at one extreme of a phenotypic range have a greater reproductive success in a particular enviornment

stabilizing selection

Favors the survival of individuals with intermediate phenotypes and selects against those with extreme phenotypes

diversifying (disruptive) selection

Favors the survival of two or more different genotypes that produce different phenotypes

balancing celection

maintains genetic diversity in a population

sexual selection

a form of natural selection by which individuals with certain traits are more likely than others to engage in successful mating

intrAsexual selection

members of one sex (usually males) directly compete with each other for the opportunity to mate with individuals of the opposite sex

intErsexual selection

members of one sex (usually females) choose their mates on the basis of certain desirable characteristics

19.5

genetic drift

genetic drift

refers to the changes in allele frequencies due to random chance

over many generations, genetic drift favors either

elimination or the fixation of an allele

genetic drift is

buffered in large populations

But it can create a huge impact on smaller populations

bottleneck effect

refers tio the change in allele frequencies of the resulting population due to genetic drift

founder effect

occurs when a small group of individuals separates from a larger population and establishes a new colony in a new location

gene flow and migration

enhance genetic diversity