Population Genetics

The letter representation of an allele/trait

• Tt, TT, tt

• What the genes say

Physical expression of an allele

• A flower being purple

A version/variant of a gene

• Long or short hair

Homozygous dominant, homozygous recessive, heterozygous

Two of the same allele, and they are both dominant

• TT

Two of the same allele, and they are both recessive

• tt

Two different alleles, one dominant, and one recessive

• Tt

p² + 2 pq + q² = 1      p + q = 1

p = frequency of the A allele

q = frequency of the a allele

p² = frequency of AA in the population

q² = frequency of aa in the population

2pq = frequency of Aa in the population

The change (over generations)

46 = 23 sets

Diploid = 2 copies of a gene (alleles)

Haploid = 1 copy of a gene

• Diploid = somatic cells

• Haploid = reproductive cells (gametes)

Two or more

Natural Selection acts on individuals but only populations evolve

A change in allele frequencies in a population over generations

1. Natural Selection = no selection

2. Genetic Drift = large breeding population

3. Gene Flow = no immigration or emigration

4. Non-Random Mating = random mating

5. Mutations = no mutations

Differences in genes or other DNA segments

Inherited genotype and environmental influences

Nope

A change in one base of a gene

When they are in the noncoding regions of the DNA or due to redundancy in the genetic code

When they change protein production → in a negative way

When they change protein production → in a positive way

If they are in the sex cells

The duplication of a small piece of DNA(won’t generally do too much damage → compared to the duplication of a chromosome portion), this gene can take on new functions through further mutations

Shuffles existing alleles into new combinations

• Recombination is more important than mutation for genetic differences

Discrete (having a widow’s peak or not, either you have it or not) and quantitative characters (skin color = a gradient; controlled by many genes)

Through gene or nucleotide variability

The average heterozygosity measures the average percent of loci that are heterozygous in a population

The measurement by comparing the DNA sequences of pairs of individuals

Genetic drift, not natural selection

Yes, many

Whether a population is evolving

a localized group of individuals capable of interbreeding and producing fertile offspring

All the alleles for all loci in a population

If all individuals in a population are homozygous for the same allele

A location

• Where on a chromosome a specific gene is

The total number of individuals divided by 2

2 alleles for each homozygous dominant individual plus 1 allele for each heterozygous individual

• Same principle for recessive

A population that is not evolving

That frequencies of alleles and genotypes in a population remain constant from generation to generation

No

Genetic variation in a population

A population that is not evolving

• Real populations have changing allele and genotype frequencies over time

Yes, they can

How allele frequencies fluctuate unpredictably from one generation to the next

Founder effect, and Bottleneck effect

Occurs when a few individuals become isolated from a larger population

• Allele frequencies in the small founder population can be different from those in the larger parent population

• For example, the minority of a population mat migrate, which does not represent the go population, but they will evolve and grow from that

A sudden reduction in population size due to a change in the environment 

• Usually associated with a natural disaster

1. Genetic drift is significant in small populations

2. Genetic drift causes allele frequencies to change at random

3. Genetic drift can lead to a loss of genetic variation within populations

4. Genetic drift can cause harmful alleles to become fixed

The movement of alleles among populations

REDUCE variation among populations overtime?

• If you have two species, A and B, and they reproduce together, both populations will almost merge, and get more and more similar to each other, reducing the variation between the two

No, it can both increase or decrease fitness

Natural Selection

• By acting on a organisms phenotype

No, because they imply direct competition

• Reproductive success is generally more subtle and depends on many factors

The contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals

1. Directional selection

2. Disruptive selection

3. Stabilizing selection

The curve shifts to the left or the right, toward one side of the spectrum

The middle of the curve collapses, both extremes have higher frequencies

The middle is the only frequency, other extremes are virtually non-existent

It occurs as the match between an organism and its environment increases

• Yes, it’s continuous because the environment can change

Natural selection for mating success

1. Intrasexual selection

2. Intersexual selection

Sexual dimorphism

Fighting between the same sex for territory

Females selecting a male to mate with(usually)

• They usually mate with males who have won territory as they are better fit

The differences between males and females of a species

• Appearance, behaviors(fighting)

When multiple alleles are maintained in a population, which results in their preservation over long evolutionary time periods

• Heterozygote advantage

• Frequency-dependent selection

The sickle-cell alleles causing mutations in hemoglobin but also confers malaria resistance

Mimicking for example; a non dangerous animal with the pattern of a poisonous one) = from google

Frequency-dependent selection selects for approximately equal numbers of “right-mouthed” and “left-mouthed” scale-eating fish

1. Selection can act only on existing variations

2. Evolution is limited by historical constraints

3. Adaptations are often compromises

4. Chance, natural selection, and the environment interact

A measurable gradient in a single characteristic (or biological trait) of a species across its geographical range.