Genetics Ch. 18: Population

Genetic Variation

Differences among individuals in the composition of their genes or other DNA segments, creates different phenotpes

Calculating genotypic frequencies

Add up # of individuals with genotype/total number of individuals

calculating allelic frequencies

number of copies of a particular allele present in a sample divided by total number of alleles

Hardy-Weinberg Law

Assumption: the population is large, randomly mating, not affected by mutation, migration, or natural selection

Prediction 1: The allelic frequencies of a population do not change

Prediction 2: the genotypic frequencies stabilize

p2

homozygous dominant allel pair frequency

q2

homozygous recessive allel pari frequency

2pq

heterozygous allel frequency

Hardy-Weinberg Equilibrium

p2 + 2pq + q2 = 1

Hardy-Weinberg Assumptions

1. No natural selection

2. no migration

3. no mutation

4. large population

5. random mating

Inbreeding Depression

when individuals with similar genotypes - typically relatives - breed with each other and produce offspring that have an impaired ability to survive and reproduce, can e a problem if all is homozygous recessive

Large Population Size

Minimizes genetic drift effects on allele frequencies.

Assortative Mating

The type of mating that occurs when an organism selects a mating partner that resembles itself, always choosing a mate based on trait

Mutation

- always happening

- must be heritable

- creating new alleles

- has a slow impact

Migration

- gene flow

- has a big impact

- between populations

- The amount of change in allelic frequency due to migration between populations depends on the difference in allelic frequency and the extent of migration

-creates variance in genotypes, then the enviroment acts on those differences

Forward and Reverse Mutations

lead to stable equilibrium

Genetic Drift

random changes in allelic frequency (sharknado)

Founder Effect

genetic drift that occurs after a small number of individuals colonize a new area

Genetic Bottleneck

Extreme reduction in genetic variation in pop due to breeding of closely related individuals, or natural disaster

Natural Selection

arises throughout the differential reproduction of individuals with many different genotypes, relative reproductive rate

Artificial Selection

selection by promoting the reproduction of organisms with traits perceived as desirable (human do this, instead of the enviroment)

Results of selection

predictable, directional slection, over dominance versus under dominance

over dominance

A condition in which the heterozygote genotype expresses a phenotype outside the range of the homozygous phenotype

under dominance

heterozygote has lower fitness than either homozygote

evolution

change in allelic frequency due to natural selction

When does natural selection occur?

When individuals with adaptive traits produce more offspring than others in the population

Fitness

measurable relative reproductive rate, determined by environment + phenotype interaction

Adaptation

trait shaped by natural selection, individuals can not choose ot adapt (does not mean sudden change)

Mutation Effects

Short Term: change in allelic frequencies

Long Term: equilibrium reached between forward and reverse mutations

Migration Effects

Short Term: change in allelic frequencies

Long Term: equilibrium reached when allelic frequencies of source and recipient populations are equal

Genetic Drift Effects

Short Term: change in allelic frequencies

Long Term: fixation of one allels (100% or 0%)

Natural Selection Effects

Short Term: change in allelic frequencies

Long Term: directional: fixation of one allele, over dominant, under dominant

Within Populations and Increase Genetic Variance

mutation, migration, some types of natural selection

Within Populations and Decrease Genetic Variance

genetic drift, some types of natural selection

Between Populations and Increase Genetic Variance

mutations, genetic drift, some types of natural selction

Between Populations and Decrease Genetic Variance

migration, some types of natural selection

Biological Evolution

genetic change in a group of organisms, variation and environmental action

evolution 2-step process

mutation and selection

Anagenesis

evolution taking place in a single group (a lineage) with the passage of time

Cladogenesis

splitting lineage into two; new species arise, "dramatic change"

Prezygotic

acts before a zygote has formed

Ecological

differences in habitat; individuals do not meet

Temporal

reproduction takes place at different times

Mechanical

anatomical difference prevent copulation

Behavioral

differences in mating behavior prevent mating

Gametic

gametes are incompatible or not attracted to each other

Prostzygotic

acts after a zygote has formed

Hyrbid Inviability

hybrid zygote does not survive to reproduction

Hybrid Sterility

hybrid is sterile

Hybrid Breakdown

F1 hybrids are viable and fertile, but F2s are inviable or sterile

Allopathic speciation

initiated by a geographic barrier to gene flow between two populations, get separated by something, can they mate?