1. ASSORTATIVE MATING ASSORTATIVE DATING
Evolutionary Mechanisms

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
Individuals 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 fair
all matings produce the same number of off- spring on average
generations do no overlap
there are no differences among genotypes in the probability of survival
Meiosis 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 MATING
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.
Sexual selection = Darwin

5. NON-RANDOM MATING
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.

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
when 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 will
result 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 heterozygosity
No change in allele frequency, only genotype frequency
Non-random mating is frequently the result of social factors, especially for genetic traits that are outwardly visible such as skin colo
Assortative 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. INBREEDING
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.

14. INBREEDING AB CD AC AA AD
Inbreeding increases
homozygosity

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 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.

17. CLASS RESULTS [2004] same different Age 9 13 Stature 6 16 Hair Color15
Eye Color 5 18
Education 19 4
Religion
Intensity 8
Economics 20 3
Residence
Hobbies
Music
Entertainment 12 11

18. SYMMETRY

19. SYMMETRY

20. SYMMETRY

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

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