Allele frequency & the gene pool | Khan Academy

Microevolution: Refers to changes in allele frequency within a population over short time scales.
Population genetics: A field that studies how allele frequencies change in populations.
Allele frequency formula:
- Allele frequency = (Number of copies of an allele) / (Total number of gene copies in a population).
Gene pool: Contains all copies of all genes in a population.

Darwin’s theory of evolution: Described as "descent with modification"; it states that species change over time and share common ancestors.
- Natural selection: Principles where organisms with beneficial heritable traits have better survival and reproductive success, leading to an increase in these traits in the population.
Other mechanisms of evolution:
- Genetic drift: Random changes in allele frequencies.
- Migration: Movement of individuals between populations affects allele frequencies.
Mendel's contribution: Introduced concepts of dominant and recessive alleles to explain heredity, complementing Darwin's ideas.

Microevolution: Involves small genetic changes in populations over generations.
Macroevolution: Refers to large-scale evolutionary changes over extended periods, such as the emergence of new species.
Relation: Both processes are the same mechanism occurring on different timescales.

Population: A group of interbreeding organisms of the same species.
Allele: A specific version of a gene, for instance, dominant allele W for purple flowers and recessive allele w for white flowers.
Genotype: The genetic makeup of an organism, indicated as combinations of alleles (e.g., WW, Ww, ww).
Phenotype: Observable characteristics or traits of an organism (e.g., purple vs. white flowers).

Allele frequency example:
- In a sample: 6 WW (purple), 1 Ww (purple), 2 ww (white) results in 13 W alleles and 5 w alleles.
- Frequencies calculated:
  - p (W) = 13/18 = 0.72 (72%)
  - q (w) = 5/18 = 0.28 (28%).
Over time, as allele frequencies change, it indicates that a population has evolved:
- Example: New generation with p (W) = 0.44, q (w) = 0.56 signifies evolution.
Genotype frequency and phenotype frequency:
- Genotype frequency: WW = 67%, Ww = 11%, ww = 22%.
- Phenotype frequency: Purple = 78%, White = 22%.
- These frequencies may differ from allele frequencies.

Gene pool: Represents the total genetic diversity within a population.
Genetic variation: A higher degree of genetic variation enhances a population's adaptability to environmental changes.
Role of natural selection: Acts on existing genetic variation to enhance survival rates among individuals in a population.