Cycle 6

Keratinocyte

Skin cells that do not produce pigment.

Melanocytes

Cells that produce pigment in keratinocytes (skin and hair cells).

Melanin

The pigment produced in melanosomes inside melanocytes.

Eumelanin

A type of melanin that is black in color.

Pheomelanin

A type of melanin that is red in color.

Allele Dominance

The B allele is dominant over both red and brown alleles, producing eumelanosomes and preventing the production of pheomelanosomes.

W allele

An allele that makes MC1R sensitive to ASP, causing it to turn on and off and produce both eumelanosomes and pheomelanosomes, resulting in brown pigment.

R allele

An allele that makes MC1R always off, but when heterozygous, the other allele is dominant and produces eumelanosomes, preventing the production of pheomelanosomes.

Mendelian Pigs Spotted Coat Colour

The S allele is a mutant version of the B allele that causes MC1R to lose function completely, resulting in red fur. However, some cells in organisms with SS genotypes mutate to be SB, allowing the MC1R to regain function and create black fur on these cells.

Hardy-Weinberg Equilibrium

If a population follows the equation p^2 + 2pq + q^2, it is at equilibrium, assuming no mutations, no migration, an infinite population size, no selection, and random mating.

Quantitative Variation

Individuals differ in small, incremental ways, creating a continuous spectrum of variation.

Qualitative Variation

Traits exist in two or more discrete states, with intermediate forms often absent.

Phenotypic Variation

Caused by genetic differences, environmental factors, or an interaction between genetics and the environment.

Gene pool

The set of all genes in a population.

Genotype frequencies

The percentage of individuals possessing each genotype (p, pq, q).

Allele frequencies

The frequency of individual alleles in a population.

Genetic equilibrium

When allele frequencies do not change between generations.

Heterozygote Advantage

Both allele frequencies are maintained at an equal amount.

Heterozygote Disadvantage

The rarer allele decreases in frequency, while the common allele increases, leading to the elimination of genetic variation.

Genetic Drift

Leads to the loss of alleles and reduced genetic variability, causing allele and genotype frequencies to differ from those predicted by the Hardy-Weinberg model.