Mutation Rates

In sexually reproducing populations, sex is
far more important than mutation in
producing the genetic differences that
make adaptation possible

Sex

True or False

Variation is  not heritable

False

Phenotypic variation

physical variation in a
trait due to environment and genetics

Genotypic variation

variation in DNA
sequence

Heritability

-proportion of variation in a trait
that is genetic

heritability =

genetic variation/phenotypic variation

True or false

All offspring reproduce equally

false

True or false

Changes in heritable traits within a population
can occur due to the unequal reproduction of
individuals

True

Gene

the functional unit of heredity

Allele

alternative forms of a gene

locus (pl. loci)

  location on a chromosome

homozygote

same 2 alleles at a locus (AA, A1A1,
etc.)

heterozygote

different alleles at a locus (Aa, A1A2,
etc.)

gametes

(egg & sperm) are haploid

zygote

 fertilized egg, diploid

Hardy‐Weinberg Equilibrium:

Expected genotype frequencies

If p and q represent the relative frequencies of the only two possible alleles (A & B) in a
population at a particular locus, then
– p2 + 2pq + q2 = 1
– where p2 and q2 are the frequencies of the
alternative homozygous genotypes and 2pq
represents the frequency of heterozygotes

Hardy ‐Weinberg Equilibrium Principle
Based on assumptions:

1. No selection
2. Mating is random (panmictic)
3. Population is infinitely large
4. No gene flow from outside population
5. No mutation

Diploidy

– Maintains genetic variation in the form of hidden
recessive alleles
– Recessive alleles in heterozygotes are not subject to
selection.

Neutral Variation

– Is genetic variation that appears to confer no
selective advantage or disadvantage
– Neutral variation cannot be removed by selection,
only by drift

Balancing Selection

– Occurs when natural selection maintains stable
frequencies of two or more phenotypic forms in a
population
– Leads to a state called balanced polymorphism
– Heterozygote advantage and frequency‐dependent
selection are two forms of balancing selection

Heterozygote Advantage

The sickle‐cell allele

– Causes mutations in hemoglobin but also
confers malaria resistance
– Exemplifies the heterozygote advantage

True or false?

Selection of an individual’s phenotype may be
affected by environmental pressures.

True

Fitness of phenotype depends on the
phenotype frequencies in the population.

FREQUENCY DEPENDENT
SELECTION

Sexual selection

-The preference of a particular phenotype in the mating decision of females and males.
-Typically females are choosier and males are more promiscuous

• Male – male competition
• Female choice based on sexually selected traits

Genetic drift

change in the genetic composition of a
population caused by chance events/
sampling error

Sampling Error

Chance differences between a sample and
the entire population
smaller sample ‐ more sampling error

The Bottleneck Effect

– A sudden change in the environment may
drastically reduce the size of a population
– The gene pool may no longer be reflective of
the original population’s gene pool

People of Pingelap suffer from a rare
disease that makes them totally colorblind

What is tis disease?

achromatopsia

Achromatopsia

-hereditary vision disorder
-colorblind, sensitive to light

Rare - affects 1 person out of

50,000 - 100,000 worldwide

The Founder Effect

– Occurs when a few individuals become
isolated from a larger population as when a
few individuals colonize an island
– Can affect allele frequencies in a population

Gene Flow

• The movement of alleles between populations
– Causes a population to gain or lose alleles
– Results from the movement of fertile individuals or gametes
– Tends to reduce differences between populations over time

What is the point
of Gene flow

homogenizing force

mixes things up until allele frequencies
are the same across populations