Nonrandom mating changes the frequency of homozygotes

Mating patterns may alter genotype frequencies if individuals in a population choose other individuals of certain genotypes as mates. For example, if they mate preferentially with individuals of the same genotype, then homozygous genotypes will be overrepresented, and heterozygous genotypes underrepresented, in the next generation in comparison with Hardy-Weinberg expectations. Alternatively, individuals

European populations of D. subobscura have

European populations of D. subobscura have

Fruit Flies Founder Effect

23.10 A Founder Effect Populations of the fruit fly Drosophila subobscura in North and South America contain less genetic variation than the European populations from which they came, as measured by the number of chromosome inversions in each population.Within two decades of arriving in the New World, the flies had increased dramatically and spread widely in spite of their reduced genetic variation.

23.10 A Founder Effect Populations of the fruit fly Drosophila subobscura in North and South America contain less genetic variation than the European populations from which they came, as measured by the number of chromosome inversions in each population.Within two decades of arriving in the New World, the flies had increased dramatically and spread widely in spite of their reduced genetic variation.

Non Random Mating

23.11 Flower Structure Fosters Nonrandom Mating The structure of flowers in plant species such as the primroses ensures that pollination usually occurs between individuals of different genotypes.

An insect visiting a thrum flower picks up pollen on its head and body. When it then visits a pin flower,

23.11 Flower Structure Fosters Nonrandom Mating The structure of flowers in plant species such as the primroses ensures that pollination usually occurs between individuals of different genotypes.

may mate primarily or exclusively with individuals of different genotypes.

An example of such nonrandom mating is provided by plant species, such as primroses (Primula), that bear flowers of two different types. One type, known as pin, has a long style (female reproductive organ) and short stamens (male reproductive organs). The other type, known as thrum, has a short style and long stamens (Figure 23.11). Pollen grains from pin and thrum flowers are deposited on different parts of the bodies of insects that visit the flowers. When the insects visit other flowers, pollen grains from pin flowers are most likely to come into contact with stigmas of thrum flowers, and vice versa. In most species with this reciprocal arrangement, pollen from one flower type can fertilize only flowers of the other type.

Self-fertilization (selfing), another form of nonrandom mating, is common in many groups of organisms, especially plants. Selfing reduces the frequencies of heterozygous individuals below Hardy-Weinberg expectations and increases the frequencies of homozygotes, without changing allele frequencies.

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