Genetic Variation and Evolution

Gene pool

Contains all different alleles for every gene in a population

Allele frequency

Number of times a specific allele occurs in a gene pool, compared to total alleles

Single-gene trait

Trait controlled by one gene, typically with 2-3 different phenotypes

Polygenic traits

Traits controlled by two or more genes, exhibiting many phenotypes

Immigration/emigration

Movement of individuals into or out of a population affecting gene pool

Non-random mating

Mate selection based on heritable traits like size or coloration

Allele

Variant form of a gene (eg. blue eye colour)

Species

Group of similar organisms capable of breeding and producing fertile offspring

Artificial selection

Breeding method where desired traits are selected for offspring

Natural Selection

Process where organisms with favorable traits survive and reproduce

Directional selection

Fitness advantage for individuals at one end of a trait spectrum

Stabilizing selection

Fitness advantage for individuals near the center of a trait spectrum

Disruptive selection

Fitness advantage for individuals at the ends of a graph, while the middle is lower. Eg. Big beaks can break big food while small beaks can get small food but medium size breaks struggle

Genetic drift

Random change in allele frequency in a small population

Bottleneck effect

Genetic drift from population reduction typically natural disasters (eg, altering genetic representation)

Founder effect

Change in allele frequencies due to migration to a small subgroup

Genetic Equilibrium

Population state where allele frequencies remain constant

Hardy-Weinberg Principle

States allele frequencies in a population remain constant unless factors cause change

Speciation

Formation of a new species

Geographic isolation

Separation of populations by geographical barriers

Sexual Selection

Natural selection based on inherited characteristics for mating success

Reproductive isolation

Barrier preventing interbreeding between species

Behavioral isolation

Interbreeding-capable populations with differences in courtship or behaviors

Temporal isolation

Reproductive isolation due to populations reproducing at different times

Neutral mutations

Mutations with no effect on phenotype or fitness

Hybrid

Usually infertile offspring from parents of different species

HOX genes

Genes controlling early embryo development, with significant impact on adult organism

Lateral gene transfer

Passing genes to non-offspring individuals, even of different species

Molecular clock

Estimates time two species have been evolving independently using DNA comparisons

Phenotype

Physical characteristics of an organism

Pre-zygotic isolation

Factors preventing formation of a zygote between different species

Post-zygotic isolation

Factors hindering development or reproduction of hybrid offspring

Natural selection acts on…

phenotype, no genotype. It acts on an organism’s characteristics, not alleles

3 sources of genetic variation

Mutations, genetic recombinations, and lateral gene transfers

what are the sources of genetic variation

1. mutations

2. genetic recombination

3. lateral gene transfer

what determines the number of phenotypes for a given trait

• number of genes that control it

• 1 gene will often have only a few phenotypes

• polygenic=many phenotypes

how does natural selection affect single-gene and polygenic traits

single gene: change in allele frequencies = change in phenotype

polygenic traits: affect the fitness of phenotype

what conditions are required to prevent genetic equilibrium

1. small population size

2. non-random mating

3. mutations

4. gene flow (immigration/emigration)

5. natural selection (THE ONLY 1 THAT INCREASES FITNESS)

what is the current hypothesis about Galapagos finch speciation

1. founder effect- small # of birds colonized islands

2. geographic isolation- birds isolated from each other

3. mutation/changes in gene pool

4. behavioural isolation (new song)

where do new genes come from?

1. duplication of existing genes

2. mutation of copy

3. new function

4. natural selection

how might HOX genes be involved in evolutionary change

small changes n regulatory genes (HOX genes) can lead to big changes in adult organisms

polygenic traits often display…

a range of phenotypes that resembles a bell curve

evolution only acts on…

populations, not individuals.

how to calculate allele frequency

specific allele\total alleles

behavioral isolation is known as…

pre-zygotic isolation. This means that these two populations are unable to form a Zygote (fertilized egg cell)

geographic isolation can result when the populations are separated by barriers such as…

1. rivers

2. mountains

3. oceans