Chapter 23 Population Genetics

Genetic variation makes ____ possible

evolution

Natural selection

where individuals that have certain inherited traits tend to survive and reproduce at higher rates than do other individuals because of those traits

Natural selection requires what?

genetic variability

Genetic variation

differences among individuals in the composition of therir genes or other DNA sequences

within a population, ____ is a result of underlying genotypic variation

phenotypic variation

Evolution acts on ____

populations

Gene variability

can be quantified as the average percentage of loci that are heterozygous

Heterozygous

Individuals that have two different alleles for a given locus

Homozygous

Individuals that have two identical alleles for a given locus

Loci

the physical location of a gene on a chromsome

Allele

the specific variant ot version of that gene

How does genetic variability originate?

when a mutation or gene duplication event produces new alleles and new genes

what is an example of a gene mutation?

Single Nucleotide Polymorphisms (SNPs)

polymorphism

two or more variations of a trait being present within a population

population genetics

the study of genes and genotypes in a population

gene pool

all the alleles for every gene in a given population

populations genetics deal with what?

allele and genotype frequencies

Genotype frequency equation

Genotype frequency = Number of individuals with a particular genotype in a population/total number of individuals in a population

Allele frequency equation

Allele frequency = Number of copies of a specific allele in a population/total number of all alleles for that gene in a population

Hardy-Weinberg equilibrium

a model used as baseline prediction of no evolutionary change (steady state)

Hardy-Weinberg model

Parents: p +q =1; Next generation: P² +2 pq + q² = 1

What does the Hardy-Weinberg model predict?

it predicts that allele and genotype frequencies will stay the same (describes a non-evolving population)

What are the assumptions that must be met for Hardy-Weinberg equilibrium to be true?

-No natural selection occurring

-No new mutations occurring

-no migration occurs between different populations

-The population is so large that allele frequencies do not change due to random sampling error

random mating

what are the causes of microevolution

1) natural selection

2) genetic drift

3) gene flow

4) nonrandom mating

What are the components of natural selection?

-genetic variation

-inheritance

-varying degrees of reproductive success

Reproductive success

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

Evolutionary fitness

fitness is an organism‘s realized ability to reproduce relative to other individuals

Directional selection

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

stabilizing selection

favors the survival of individuals with intermediate phenotypes

disruptive selection

occurs when conditions favor individuals at both extremes of a phenotypic range

balancing selection

maintains genetic diversity (two or more alleles are kept in balance and maintained over many generations)

genetic drift

changes allelic frequency due to random chance unrelated to fitness; usually favors total loss (0%) or fixations (100% of the population) of an allele

genetic drift can be influenced by what effects?

the bottleneck effect and founder effect

bottleneck effect

when a population is reduced dramatically and then rebuilds without some alleles from the previous gene pool

founder effect

when a small group separates from a larger population

gene flow

when individuals migrate between populations having different allele frequencies; tends to enhance genetic diversity within a population

Nonrandom mating/sexual selection

when individuals choose mates based on phenotypes which can cause evolution can occur

intrasexual selection

describes competition among members of the same sex

intersexual selection

describes competition between members of the opposite sex

adaptations are often ___

compromises (trade offs)

Evolution ___ result in perfect organisms

does NOT

sexual dimorphism

a difference in secondary sexual characteristics between male and females of the same species

microevolution

a change in allele frequencies in a population over generations

Phenotype plasticity

the ability of an individual genotype to produce different phenotypes when exposed to different environmental conditions

frequency-dependent selection

the fitness of a phenotype depends on how common it is in the population

heterozygote advantage

individuals who are heterozygous at a particular locus have greater fitness than do both kinds of homozygotes