Glossary
Allele Frequencies
The proportion of a specific allele (a variant of a gene) within a population's gene pool.
Example:
In a population of flowers, if 70% of all color genes are for red petals and 30% are for white petals, these are the allele frequencies.
Dominant Allele (p)
An allele that expresses its phenotype even when only one copy is present in a heterozygous individual; 'p' represents its frequency in Hardy-Weinberg equations.
Example:
In pea plants, the allele for purple flowers (P) is dominant. If 80% of all flower color alleles in a population are P, then p = 0.8 for the dominant allele.
Gene Flow
The transfer of alleles or genes from one population to another, typically through the migration of individuals.
Example:
When a group of birds from one island flies to another island and interbreeds with the resident bird population, it introduces new alleles through gene flow.
Genetic Drift
Random fluctuations in allele frequencies in a population, particularly pronounced in small populations, due to chance events.
Example:
In a very small population of wildflowers, a sudden storm randomly kills many plants, leading to a significant, non-adaptive change in the frequency of flower color alleles; this is genetic drift.
Genotype Frequencies
The proportion of individuals in a population that possess a specific combination of alleles (genotype) for a given gene.
Example:
If 25% of a beetle population are homozygous dominant (BB), 50% are heterozygous (Bb), and 25% are homozygous recessive (bb), these represent the genotype frequencies.
Hardy-Weinberg Equilibrium
A theoretical model describing a population where allele and genotype frequencies remain constant across generations, indicating that no evolution is occurring.
Example:
If a population of imaginary 'sparkle-dogs' maintains the same frequency of the sparkle allele (S) and dull allele (s) over many generations, it's in Hardy-Weinberg Equilibrium.
Heterozygous (2pq)
An individual possessing one dominant and one recessive allele for a specific gene; '2pq' represents its frequency in a population.
Example:
If the frequency of the dominant allele (A) is 0.6 and the recessive allele (a) is 0.4, then 2 * 0.6 * 0.4 = 0.48, meaning 48% of the population is expected to be heterozygous (Aa).
Homozygous Dominant (p²)
An individual possessing two copies of the dominant allele for a specific gene; 'p²' represents its frequency in a population.
Example:
If the frequency of the dominant allele for tallness (T) in a plant population is 0.7, then 0.7² = 0.49, meaning 49% of the plants are expected to be homozygous dominant (TT).
Homozygous Recessive (q²)
An individual possessing two copies of the recessive allele for a specific gene, thus expressing the recessive phenotype; 'q²' represents its frequency in a population.
Example:
If 9% of a population of fruit flies have white eyes (recessive trait), then 0.09 represents the frequency of homozygous recessive individuals (ww).
Mutation
A permanent change in the DNA sequence of an organism, which can introduce new alleles into a population and alter allele frequencies.
Example:
A sudden change in a gene causes a new allele for resistance to a pesticide to appear in an insect population; this is a mutation.
Null Hypothesis
In the context of Hardy-Weinberg, it's the hypothesis that there is no significant difference between observed allele/genotype frequencies and those predicted by the model, implying no evolution is occurring.
Example:
When scientists compare observed allele frequencies in a real population to the Hardy-Weinberg predictions, they are testing the null hypothesis that the population is not evolving.
Random Mating
A mating pattern where individuals choose mates without regard to their genotype or phenotype, ensuring allele combinations are purely by chance.
Example:
If a population of fish mates without any preference for size, color, or specific traits, they are exhibiting random mating.
Recessive Allele (q)
An allele whose phenotype is only expressed when two copies are present (homozygous recessive); 'q' represents its frequency in Hardy-Weinberg equations.
Example:
For human eye color, the blue eye allele (b) is recessive. If 20% of all eye color alleles in a population are b, then q = 0.2 for the recessive allele.
Selection
A process where certain genotypes have a differential survival and reproduction rate due to environmental pressures (natural selection) or human intervention (artificial selection).
Example:
In a forest, green beetles are camouflaged better than brown beetles, leading to more green beetles surviving and reproducing; this is an example of selection.