intro to evolution exam 2 study guide

Population

a group of interacting and potentially interbreeding individuals of the same species

Genetic locus

location of a specific gene or sequence of DNA on a chromosome

Homozygous

individual carries two copies of the same allele at a locus

Heterozygous

individual carries different alleles at a locus

what are the 5 assumptions of the hardy-weinberg equilibrium?

Population is infinitely large

Genotypes do not confer differences in fitness

There is no mutation

Mating is random

There is no migration

if the hardy-weinberg equilibrium is true:

Allele frequencies do not change

No evolution occurs

What is so special about mutation?

It is the ultimate source of genetic variation

Natural selection acts on the:

individual

Evolution acts on the:

population

p² =

probability of A1A1

2pq=

probability of A1A2

q² =

probability of A2A2

Fitness

the survival and reproductive success of an individual with a particular phenotype

What are the components of fitness?

Survival to reproductive age

Mating success

Fecundity

Relative fitness (w)

contribution of individuals with one genotype compared with the average contribution of all individuals in the population

What does selection directly operate on?

Phenotypes of organisms

Negative selection

Alleles that decrease fitness experience

Positive selection

Alleles that increase fitness experience

Pleiotropy

mutation in a single gene affects more than one phenotypic trait

Antagonistic pleiotropy

beneficial effects for one trait but detrimental effects for other traits
-Net effect on fitness determines outcome of selection(context dependant)

Selection is always:

context dependent

Dominance

dominant allele masks presence of recessive allele in heterozygote

Additive alleles

homozygous condition yields twice the phenotypic effect for the gene as compared with heterozygotes

what is the neutral theory of molecular evolution?

-most mutations are selectively neutral
-much of the genetic variation within/between species is the result of random genetic drift

what are the actions that causes genetic drift?

Imperfect sampling causing some alleles to be underrepresented relative to others(sampling biase)

what does it mean when an allele is fixed?

no genetic variation at a locus within a population because all the individuals are genetically identical at that locus

What does a bottleneck result in?

A nonrepresentative set of alleles for subsequent populations, even after the population size rebounds

What is a founder effect?

A type of bottleneck resulting from a small number of individuals colonizing a new, isolated habitat

an example of a founder effect:

Migrating birds disperse a few plant seeds to a remote island, where a new population forms

what can cause population subdivision?

depends on landscape features and the relative degree of motility of individuals in the population

polygenic traits are influenced by:

multiple genes and generate a normal distribution
epistasis, & Interaction with environment

what is an example of polygenic traits?

human height

epistasis

interaction between alleles
occurs when the effects of an allele at one locus are modified by alleles at one or more other loci

phenotypic plasticity

Interaction with environment

Quantitative genetics

study of the genetic mechanisms and evolution of continuous phenotypic traits

what is an example of epistasis occuring in humans?

The bald genotype in the gene for hair or baldness overrides the effects of alleles in genes for hair color.

what is an example of epistasis occuring in rats?

Two “without pigmentation” alleles for the pigmentation gene in mice override coat color alleles in other genes.

Vp

total phenotypic variance in population

Vg

variance due to genetic differences

Ve

variance due to environmental differences

what is the need for Genome-wide association (GWAS) and QTL

-identifies regions of the genome associated with phenotypic variation
-First step toward elucidating genes responsible for phenotypic evolution
-Within humans, used to find genetic basis of specific diseases and disorders

what is phenotype plasticity?

A single genotype produces different phenotypes depending on the environment

complex adaptations

Coexpressed traits that experience selection for a common, often novel, function

Promiscuous proteins

capable of carrying out two functions; are especially likely to take on new functions if duplicated

Paralog

a homologous gene that arises by gene duplication

Gene recruitment

the co-option of a particular gene or network for a totally different function as a result of a mutation; the reorganization of a preexisting regulatory network can be a major evolutionary event

what is venom?

Complex secretion of toxic peptides and enzymes (at least in herps) that is produced in a specialized gland and delivered to target animal through wound (e.g., bite, sting)

what is a pseudogene?

a non-functional copy of a functional gene

what gene in vertebrates that was duplicated twice?

Hox

what happens when the Hoxd13 gene is turned on later in fin development?

it causes the production of cartilaginous ball of cells

what happens when Bmp2 expression is chanfed?

the driving of rapid cell devision in developing didgets

Convergent evolution

Independent evolution leading to similar traits in two different lineages

Result of similar selection pressures

what is an example of convergent evolution?

the development of the eye

how was crysrallins evolved?

by gene recruitment

what is deep homology?

When growth and development of traits in different lineages result from underlying mechanisms inherited from a common ancestor

Is the fly eye homologous to the mouse eye, 

or is it convergent?

Both, depending on the level of development examined.

Opsin usage vs eye structure

Parallel evolution

Independent evolution of similar traits in multiple lineages, all starting from a similar ancestral condition (e.g., three-spined stickleback)
lake of pressure and time

what are some constraints on evolution?

-The laws of physics

-Pleiotropy

-Antagonistic pleiotropy

Antagonistic pleiotropy

Single gene affects expression of many traits; mutations may have positive effects for one trait but negative effects for another trait

Pleiotropy

ability that genes have to exert more than one phenotypic effect

The laws of physics

e.g., atmospheric O₂ concentrations constrain insect size

what is an example of antagonstic pleiotropy?

the number of cervical vertebrae being 7 due to hox gene regulation