Population Genetics

Population

group of individuals living in the same area that can breed with each other

Gene Pool

collection of alleles found in a population

Allele Frequency

how common is an allele within the population

Evolution

any change in allele frequencies within a population over time (Populations evolve, not individuals)

How can we measure changes?

Hardy-Weinberg equilibrium

Hardy-Weinberg equilibrium

describes situation with no evolution

Hardy-Weinberg equilibrium

p + q = 1 p2 + 2pq + q2 = 1

p=

frequency of most common allele, ex. A

q=

frequency of less common allele, ex. a

p2

frequency of homozygous AA individuals

2pq

frequency of heterozygous Aa individuals

q2

frequency of homozygous aa individuals

Hardy-Weinberg equilibrium - Requirements

-Very large population (no genetic drift)
• No migration (no gene flow in or out)
• No mutations (no new alleles)
• Random mating (no mating preferences)
• No selection (everyone is equally fit

If Hardy-Weinberg equilibrium is not met….

allele frequencies are changing and the population is evolving

Hardy-Weinberg - Applications p+q=1

• Two alleles = W (wings),
w (no wings)
• Frequency of dominant allele (W) = p
• Frequency of recessive allele (w ) = q
• Allele Frequencies must add to 1 (100%)

Hardy-Weinberg - Applications p2 + 2pq + q2 = 1

• (Homozygous) Recessive Genotype Frequency (
w w ) = q2
• Homozygous Dominant Genotype Frequency (WW) = p2
• Heterozygous Genotype Frequency (Ww ) = 2pq
• Genotype Frequencies must add to 1 (100%)

Bottle neck

When a population is greatly reduced in size, often due to a
catastrophic event, limiting the genetic diversity of the species.

Genetic Drift

Variation in the relative frequency of different genotypes in a
small population, owing to the chance disappearance of particular
genes as individuals die or do not reproduce.

Founders effect

A founder effect, as related to genetics, refers to the reduction
in genomic variability that occurs when a small group of
individuals becomes separated from a larger population.

Cheetahs have very little genetic diversity. It is theorized that they
narrowly escaped the last ice age and as few as one litter are the source of
all modern day cheetahs

Bottleneck

A Beetle population has multiple color Alleles but most of the ones of a
certain color are killed due to a random event, leaving the other colors
more likely to reproduce and be more frequent.

Genetic Drift

Ellis Van Creveld Syndrome is a recessive genetic disorder that can lead to
six fingers on each hand and is more common in Amish due to their limited
populations that derived from very few founders.

Founder’s effect