Presentation on theme: "ASSORTATIVE MATING ASSORTATIVE DATING"— Presentation transcript:
1 ASSORTATIVE MATING ASSORTATIVE DATING Evolutionary Mechanisms
2 HARDY-WEINBERG EQUILIBRIUM (1) random mating(2) equal number of malesand females(3) the population isinfinitely large(4) there is no migrationin or out(5) natural selection, mutation, & geneticdrift are not acting on the populationIndividuals mate at random:Sexual selection: Some individuals may be more successful at finding mates than others. Since males are typically the limiting sex (Bateman's principle), the differences typically arise either as a result of male-male competition or female choice.
3 HARDY-WEINBERG EQUILIBRIUM meiosis is fairall matings produce the same number of off- spring on averagegenerations do no overlapthere are no differences among genotypes in the probability of survivalMeiosis is fair. More specifically, we assume that there is no segregation distortion, no gamete competition, no differences in the developmental ability of eggs, or the fertilization ability of sperm.Segregation distortion: The two alleles are not equally frequent in gametes produced by heterozygotes. The -allele in house mice, for example, when in heterozygous form is found in 95% of fertile sperm.Gamete competition: Gametes may be produced in equal frequency in heterozygotes, but there may be competition among them to produce fertilized zygotes, e.g., sperm competition in animals, pollen competition in seed plants.All matings produce the same number of progeny.Fertility selection: The number of offspring produced may depend on maternal genotype (fecundity selection), paternal genotype (virility selection), or on both.Survival does not depend on genotype.* Viability selection: The probability of survival from zygote to adult may depend on genotype, and it may differ between sexes.
4 NON-RANDOM MATINGSome individuals may be more successful at finding mates than others. Since males are typically the limiting sex (Bateman's principle), the differences typically arise either as a result of male-male competition or female choice.Sexual selection = Darwin
5 NON-RANDOM MATINGIf individuals (usually females) are choosy in their selection of mates the gene frequencies may become altered.Darwin called this sexual selection.Breeding territories, courtship displays, "pecking orders" can all lead to it.In each case certain individuals do notget to make their proportionatecontribution to the next generation.
9 SEXUAL SELECTION Drawbacks -- Differential contributions to the next generation.Eventually, sexual selection will come up against opposing forces of viability selection. Traits that are too conspicuous will exposeindividuals to predation.
10 ASSORTATIVE MATINGMating of individuals that are phenotypically similar.Such individuals are more likely to carry the same alleles for genes determining morphologywhen assortment is based on some aspect of the phenotype, it may be influenced by both genetic and environmental factors.assortative mating may affect the transmission, magnitude, and correlation of both genetic and environmental effects
11 ASSORTATIVE MATING Positive -- Individuals show a preference for their own phenotype (most common)Reproductive isolation among between sympatric species may sometimes be viewed as a form of assortative mating.Complete positive assortative mating willresult in speciation.
12 SOCIAL FACTORS & EFFECTS Non-random mating is frequently the result of social factors.Mating for other traits is essentially random.Assortative mating increases homozygosity at the expense of heterozygosityNo change in allele frequency, only genotype frequencyNon-random mating is frequently the result of social factors, especially for genetic traits that are outwardly visible such as skin coloAssortative mating with respect to one trait usually leaves mating with respect to other traits essentially random.For example, tall men may mate with tall women, but since stature is not related to blood type, mating with respect to the ABO blood system should be random.
13 INBREEDINGMatings between close relatives is a special case of assortative mating.The closer the kinship, the more alleles sharedPredisposes to homozygosity.Potentially harmful recessive alleles - invisible in the parents - become exposed to the forces of natural selection in the children.Many species have mechanismswhich help them avoid inbreeding.
15 TYPES OF ASSORT. MATING Negative -- Purposeful avoidance of mate with a similar phenotype
16 ASSORTATIVE MATING VS. INBREEDING Assortative mating leads to nonrandom patterns of matingThe basis for assortative mating is not relatedness but phenotypic similarity or dissimilarity. Both processes sort existing variation, altering genotypic frequencies within populations. Inbreeding and assortative mating do not dramatically alter allele frequencies. Highly significant consequencesfor the evolution of populations.
17 CLASS RESULTS  same different Age 9 13 Stature 6 16 Hair Color 15Eye Color518Education194ReligionIntensity8Economics203ResidenceHobbiesMusicEntertainment1211