A botanist studying water lilies in an isolated pond...

A botanist studying water lilies in an isolated pond observed three leaf shapes in the population: round, arrowhead, and scalloped. Marker analysis of DNA from 125 individuals showed the round-leaf plants to be homozygous for allele $r 1$, while the plants with arrowhead leaves were homozygous for a different allele at the same locus, $r 2 .$ Plants with scalloped leaves showed DNA profiles with both the $r 1$ and $r 2$ alleles. Frequency of the $r 1$ allele was estimated at $0.81 .$ If the botanist counted 20 plants with scalloped leaves in the pond, what is the inbreeding coefficient $F$ for this population?

Key Concepts

Deviation from Expected Genotypic Frequencies

Deviation from expected genotype frequencies is detected when the observed distribution, particularly of heterozygotes, differs from the frequencies predicted by the Hardy-Weinberg equilibrium. Such deviation is used to calculate the inbreeding coefficient by comparing observed and expected heterozygote frequencies, with a reduction indicating inbreeding.

Allele Frequency

Allele frequency is the proportion of a particular allele among all allele copies at a specific genetic locus in the population. It provides a measure of how common an allele is and forms the basis for predicting genotype frequencies under models such as the Hardy-Weinberg equilibrium.

Hardy-Weinberg Equilibrium

The Hardy-Weinberg equilibrium describes a theoretical state in which allele and genotype frequencies in a population remain constant from generation to generation, assuming random mating and no influences from mutation, migration, selection, or genetic drift. It provides expected genotype frequencies based on allele frequencies, such as the heterozygote frequency being 2p(1-p).

Inbreeding Coefficient

The inbreeding coefficient (F) is a measure of the degree of inbreeding in a population, indicating the probability that two alleles at a locus are identical by descent. Inbreeding increases the frequency of homozygotes and decreases the heterozygote frequency compared to expectations under random mating.

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