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Presentation on theme: "ASSORTATIVE MATING ASSORTATIVE DATING Evolutionary Mechanisms."— Presentation transcript:


2 HARDY-WEINBERG EQUILIBRIUM (1)random mating (2)equal number of males and females (3)the population is infinitely large (4)there is no migration in or out (5) natural selection, mutation, & genetic drift are not acting on the population

3 (5) meiosis is fair (6) all matings produce the same number of off- spring on average (7) generations do no overlap (8) there are no differences among genotypes in the probability of survival HARDY-WEINBERG EQUILIBRIUM


5  If 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 not get to make their proportionate contribution to the next generation. NON-RANDOM MATING




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 expose individuals to predation.

10 ASSORTATIVE MATING  Mating of individuals that are phenotypically similar.  Such individuals are more likely to carry the same alleles for genes determining morphology

11 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 will result in speciation. ASSORTATIVE MATING

12  Non-random mating is frequently the result of social factors.  Mating for other traits is essentially random. SOCIAL FACTORS & EFFECTS  Assortative mating increases homozygosity at the expense of heterozygosity  No change in allele frequency, only genotype frequency

13  Matings between close relatives is a special case of assortative mating.  The closer the kinship, the more alleles shared  Predisposes to homozygosity.  Potentially harmful recessive alleles - invisible in the parents - become exposed to the forces of natural selection in the children.  Many species have mechanisms which help them avoid inbreeding. INBREEDING

14 ABAB CD ACAC AA ADAD Inbreeding increases homozygosity INBREEDING

15 Negative --  Purposeful avoidance of mate with a similar phenotype TYPES OF ASSORT. MATING

16  Assortative mating leads to nonrandom patterns of mating  The 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 consequences for the evolution of populations. ASSORTATIVE MATING VS. INBREEDING

17 CLASS RESULTS [2004] Age913 Stature616 Hair Color156 Eye Color518 Education194 Religion185 Intensity158 Economics203 Residence203 Hobbies158 Music194 Entertainment1211 samedifferent




21  tracing the change in spousal resemblance over time,  analyzing the resemblance between the spouses of biologically related individuals MEASURING ASSORTATIVE MATING Dad’s height Mom’s height

22 Mechanisms that change gene frequencies:  natural selection  genetic drift  bottlenecks and founder effects  assortative mating  inbreeding EVOLUTIONARY FACTORS

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