These two chapters are rather technical, but I encourage you to think beyond the details and formulas and try to think of the biological implications and the bigger picture. Chapter 17, on parent-offspring regression, is a bit out-dated, as methods to estimate quantitative genetic parameters have been developed a lot since 1998, particularly the so-called "Animal Model".
Chapter 7, however, contains some general information that has important biological and evolutionary implications also today. I would particularly like to highlight the crucial evolutionary role of assortative mating, an underestimated evolutionary force. I say "underestimated", because assortative mating might be perceived as uninteresting and unimportant, since it only changes genotype frequences, not allele frequencies. Assortative mating (=positive correlation between the characters of mates), increases the frequency of homozygotes in a population, and hence "flattens" the trait distribution and increases the additive genetic variance. This is because extreme individuals at the tails of the trait distributions (homozygotes) increase at the expense of individuals close to the mean (heterozygotes); a higher frequency of homozygotes are produced when parents mate assortatively.
How can then assortative mating affect the additive genetic variance and the response to selection? In chapter 7, consider Figs. 7.7 (theory) and Example 4 (empirical results from an experiment on assortative mating experiment on Drosophila).
In Fig. 7 it can be seen that with a relative moderate phenotypic correlation between the traits of parents (r = 0.5), the additive genetic variance increases and becomes twice the amount as under the situation of random mating (r = 0)! This is a huge amount, and it happens without any particular molecular mechanism or changed gene experession etc., it simply an effect of the fact that "likes mates with like", which results in a higher frequency of homozygotes in the population.
Note that, interestingly, with disassortative mating (r < 0), the additive genetic variance does not decrease as much, but instead hovers around 90 % of the expected variance under random mating (Fig. 7.7). These theoretical expectations are largely confirmed in the experiment presented in Example 4.
Discuss the evolutionary implications of assortative mating as a means of increasing the additive genetic variance without affecting allele frequencies! Can you think of any implications in conservation biology, for instance, in terms of population "rescue" of small populations threatened by genetic drift?
Chapter 7, however, contains some general information that has important biological and evolutionary implications also today. I would particularly like to highlight the crucial evolutionary role of assortative mating, an underestimated evolutionary force. I say "underestimated", because assortative mating might be perceived as uninteresting and unimportant, since it only changes genotype frequences, not allele frequencies. Assortative mating (=positive correlation between the characters of mates), increases the frequency of homozygotes in a population, and hence "flattens" the trait distribution and increases the additive genetic variance. This is because extreme individuals at the tails of the trait distributions (homozygotes) increase at the expense of individuals close to the mean (heterozygotes); a higher frequency of homozygotes are produced when parents mate assortatively.
How can then assortative mating affect the additive genetic variance and the response to selection? In chapter 7, consider Figs. 7.7 (theory) and Example 4 (empirical results from an experiment on assortative mating experiment on Drosophila).
In Fig. 7 it can be seen that with a relative moderate phenotypic correlation between the traits of parents (r = 0.5), the additive genetic variance increases and becomes twice the amount as under the situation of random mating (r = 0)! This is a huge amount, and it happens without any particular molecular mechanism or changed gene experession etc., it simply an effect of the fact that "likes mates with like", which results in a higher frequency of homozygotes in the population.
Note that, interestingly, with disassortative mating (r < 0), the additive genetic variance does not decrease as much, but instead hovers around 90 % of the expected variance under random mating (Fig. 7.7). These theoretical expectations are largely confirmed in the experiment presented in Example 4.
Discuss the evolutionary implications of assortative mating as a means of increasing the additive genetic variance without affecting allele frequencies! Can you think of any implications in conservation biology, for instance, in terms of population "rescue" of small populations threatened by genetic drift?
