Key Concepts in Population Genetics and Evolutionary Forces

Which two forces decrease the genetic variation within a population?

selection and drift

Which two forces increase genetic variation within a population?

Migration and mutation

Which two forces increase differentiation within a population?

genetic drift and mutation

Which force decreases differentiation within a population?

Migration

new population starts from a few individuals, causing reduced genetic variation

founder effect

random changes in allele frequency, stronger in small populations

genetic drift

What is the term for the size of an ideal population that would lose genetic variation at the same rate as the real population?

Effective population size

What is the formula for effective population size?

Ne = (4NmNf) / (Nm + Nf)

What are the three conditions needed for natural selection to occur?

variation, differential survival, heritability

the transmission of traits from one generation to the next

Mendelian Genetics

frequency of traits (and alleles) changes over time in a population

population genetics

the allele has reached a frequency of 100% in a population

fixation

Sharp population drop reduces genetic diversity, leaving survivors with limited allele variation.

bottleneck effect

fitness of a genotype standardized by comparison to other genotypes (population average)

relative fitness

True or false: Evolution happens for the good of the species.

false

Assumptions of Hardy-Weinberg Equilibrium

no selection, no mutation, no migration, large population, random mating

are not susceptible to either sick-cell anemia or malaria; fitness is equal to or better than homozygote HbA

HbA/HbS

susceptible to sickle-cell anemia but not malaria; alway has negative effects on fitness

HbS/HbS

susceptible to malaria but not sick-cell anemia; fitness is high without malaria risk, but low when malaria is present

HbA/HbA

Suppose an entire village in a very wet region escaped mosquitos by moving to a dry region. The frequency of HbS/HbS genotypes in this population will:

decrease in the population since malaria is no longer a selective force

What is necessary for a population to evolve via natural selection?

phenotypic variation, heritable basis for that variation, differential fitness based on that variation

what best explains whether a new allele will persist in a population?

drift; depends on population size

when there is no selection, which allele is more likely to get fixed in a small population?

either allele by chance

under what conditions would there be very little genetic drift for a gene in a population?

if there is 1 allele

what of the three villages (large, med, small) would be least likely to have allele frequencies at HW equilibrium?

small

Phenotypic variation formula

Vp = Vg + Ve

do all genetic differences have the same effect on a phenotype?

no (anything that isn't due to genetics must be due to environmental factors and is not heritable)

what is genetic polymorphism?

the simultaneous occurrence of two or more discrete phenotypes within a population (mendelian inheritance)

what is Epistasis

A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited.

what is quantitative traits

polygenic (influenced by many genetic loci), show continuous variation, and may show phenotypic plasticity (variation due to environment)

variance due to genetic differences

additive, dominance, interaction between alleles (epistasis), variation in plastic traits

narrow-sense heritability

the proportion of total phenotypic variance that can be explained by additive genetic variation (Va)

Heritability (h^2)

slope

does selection act on phenotype or genotypes?

phenotypes

does evolution happened when there is a change in allele or phenotype frequency?

allele

selection can lead to evolution if...

differential reproduction is tied to genetic variation

part of heritability that causes populations to respond predictably to natural selection

additive variation

favors one extreme trait

directional selection

favors the average trait

stabilizing selection

favors both extreme traits

disruptive selection

the capacity for a genotype to express more than one phenotype, depending on the environment; flexible adaptation

phenotypic plasticity

What of the following is necessary for the evolution of finch beak size on Daphne Major?

A. beak size had to be at least partially determined by the additive effects of alleles

B. characteristics of the average seed had to change from year to year

C. individuals with smaller beaks had to grow larger beaks duringdrought years

A

suites of coexpressed traits that together experience selection for a common function; influenced by multiple environmental and genetic factors

complex adaptation

a system of interacting genes, transcription factors, promoters, RNA and other molecules that functions like a biological circuit

regulatory networks

What controls when/where a gene is expressed, tell a cell where it is in developing embryo?

cis-regulatory regions

how does gene duplication affect regulatory networks?

Gene duplication adds extra genes that can evolve new or specialized regulation, expanding the network.

homologous genes that arise by duplication (present in the same species)

paralogs

this gene may end up in a different regulatory network

recruitment

(proteins with >1 function) are especially likely to take on new functions after duplication

promiscuous proteins

Why are regulatory networks often involved in complex adaptations?

Because they control how many genes interact, small regulatory changes can create big, coordinated effects

Some evolutionary biologists argue that changes in the regulation ofgenes, rather than changes in the coding sequence, are more likely to beinvolved in adaptation. Which of the following statements forms part ofthe basis for this argument:

a) Coding sequence changes are constrained because most genes performmultiple functions

b) Regulatory mutations are more likely to occur than coding sequencemutations

c) Regulatory changes likely affect all processes that a gene is involved in

A

growth/development of traits result from genetic mechanisms inherited from common ancestor

deep homology

homologous genes separated by a speciation event

orthologs

organizes an embryo from back (dorsal) to belly (ventral) using signaling gradients that direct cell fate

dorsal-ventral patterning

homologous genes that arise by duplication

paralogs

opsins evolved from the same ancestral opsin

homologous

crystallins were borrowed from different genes

convergent

human children born with an abnormal number of cervical vertebrae are 120x more likely to develop pediatric cancers

antagonistic pleiotropy

breeders equation

R (response to selection) = h^2 (heritability; slope) x S (selection strength)

Several species of finch's evolved to have different beak shapes to occupy a specific niche on the Galapagos islands.

Darwin's finches

Oldfield mice

.

stretch of DNA correlated with variation in phenotype

quantitative trait locus

nonrandom association of alleles at different loci

linkage disequilibrium

Are phenotypic differences due to a few loci with large effects, or to many loci with small effects?

Usually many loci with small effects, though some traits involve a few with large effects

diff phenotypes for marine (more predators) vs freshwater (less predators). more lateral plates protects against predators. less plates allows to grow larger, breed sooner. costs of certain adaptation.

threespine sticklebacks

structure constructed by an organism that can influence its performance or success; reflects its genotype despite not being part of its body

extended phenotype

evolution driven by competition between species; traits evolved in opposite directions, minimizing phenotypic overlap between species

ecological character displacement

the process of domestication likely began as a result of us imposing selection for traits other than those found in wild relatives (i.e., changing the fitness associated with particular traits)

artificial selection

combining and mixing of chromosome during formation of offspring; includes both meiosis and fertilization

sex

asexual reproduction in which the ovum develops without fertilization

parthenogenesis

Through recombination, meiosis allows paired chromosomes to cross over, creating unique combinations of alleles

generating novel genotypes

the process by which the genomes of an asexual population accumulates deleterious mutations in an irreversible manner

Muller's rachet

for co-evolving populations to maintain relative fitness, each population must constantly adapt to the other

Red Queen effect

size imbalance between gametes

anisogamy;

females: produce large gametes (eggs)

males: produce small gametes (sperm)

differential reproductive success resulting form the competition for fertilization

sexual selection

The potential reproductive capacity of a female

fecundity

the ratio of males to females capable of reproducing at a given time

operational sex ratio

one male pairs with one female;

sexual: partners mate exclusively

social: partner pair but may cheat

monogamy

male mates with multiple females

polygyny

female mates with multiple mates

polyandry

we should expect to see more evidence of sexual selection when operational sex ratios are _________ and variance in reproduction is __________.

highly skewed; high

difference in form between males and females

sexual dimorphism

attractive traits that increase mating success

ornaments

'presents' to females to encourage preference

nuptial gifts

weaponry used to outcompete other individuals or ensure mating success

armaments

traits that confer a fitness benefit on one sex but cost to the other

sexual conflict

In water striders, sexual conflict has resulted in the growth of projections on the legs and antennae of male water strider to prevent the female from escaping. Growth of the wrench-like extensions is controlled by dll, which is crucial in the development of appendages (legs, wings, antennae). This additional function likely resulted from:

A. A change in gene regulation

B. A change in a proteincoding gene

C. A change in plastic responses to environmental stimuli

A

benefits the a particular female receives (e.g., food, nest sites, protection)

direct benefits

benefits that affect the genetic quality of a female's offspring (e.g., male offspring that are more desirable to females)

indirect benefits

females choose attractive males so their sons inherit those traits and gain more mates

sexy sons hypothesis

the investment an organism makes in growth and reproduction

life-history

A wing spur is a hard, pointed structure on a bird's wing used for fighting or defense

wing spur

competition between siblings for parental attention, food, or resources.

Sibling rivalry (or offspring-offspring conflict)

mothers alter sex ratio depending on conditions;

Females in good condition - produce sons (sons in good condition may get many mates)

Females in poor condition - produce daughters (daughters have a high probability of mating).

Females favored with high resources - Up to three helping daughters beneficial

Males favored with low resources - Disperse away from poor habitat

Trivers-willard hypothesis

the silencing of either the maternal or paternal copy of a gene by DNA methylation, resulting in altered gene expression

Genomic imprinting

Which mating system is most likely toproduce parental conflict?

A. Males and females partner for life and share parenting duties

B. Females mate once but males mate multiple times

C. Females and males mate multiple times

D. Males mate once but females mate multiple times

C

older women live past menopause to help care for grandchildren, increasing family survival and passing on their genes.

grandmother hypothesis

a common ancestor and all of its descendant taxa

monophyletic

a common ancestor and some, but not all, of its descendant taxa

paraphyletic

a group that contains two or more taxa but does not contain the most recent ancestor of those taxa

polyphyletic