Evolution Chapter 21 Notes

NOTE 21A: Gene conversion arises because during recombination, a hybrid DNA double helix is formed, with one strand from one genome and one strand from the other. Sites that are heterozygous (i.e., carry different bases in the two genomes of the diploid) will now be mismatched within one double helix and will be repaired in one or the other direction. This process of mismatch repair is usually biased.

NOTE 21B: This is a very simple caricature. One might, for example, write down differential equations for the change in amount of coat protein and polymerase through time. However, the simple model captures the main features.

NOTE 21C: Recall that fig wasps are haplodiploid: If the mother fertilizes her eggs, they will develop as diploid females, whereas if she does not allow them to be fertilized, they will grow up as haploid males.

NOTE 21D: This kind of variation in offspring quality is commonly due to selfing. Selfed progeny typically suffer strong inbreeding depression (see p. 515). Here, we ignore the different relationships between selfed and outcrossed progeny, and we also simplify by assuming just two kinds of seed: high and low quality.