Chapters 24 and 25: On the effects of short- and long-term selection on genetic variance

These chapters are rather technical and very mathematical. However, there are some interesting and general messages, that deserves to be carefully considered. Here are some questions to consider:

1. Which two main models about genetic variance have been developed and which assumptions underly them?

2. Sometimes, an initial increase in genetic variance is observed in an early stage of the selection experiment? Which of the two models can explain this, and what is the reason by behind such an increase in additive genetic variance?

3. What time frames are we talking about here we say "short-term" and "long-term"?

4. How do a/the effect size of loci and b/the number of loci affect the selection plateau?

5. How is allele frequency dynamics and hence additive genetic variance changing over time in "mixed models", i. e. genetic architectures characterized by a few loci of major effect and many loci of small effect?

Chapters 18 and 21 (Thursday November 4)

These two chapters are rather technical, and focussed on the statistical details of estimation procedures. I would encourage you to not "get drowned in the details" but try to see the bigger picture and the biological implications. Much has happened in the past decade, and the estimation procedures that are described have, to some extent, been replaced by more modern and powerful methods, such as the "Animal Model".


Nevertheless, there are some general and interesting questions that should be discussed:


Chapter 18: Why are heritability estimates from full-sib analyses often higher than those from parent-offspring regressions? Which genetic factors are responsible for the higher heritability estimates  obtained in full-sib analyses? Which procedures are preferrable: parent-offspring regression, half-sib analyses or full-sib analyses? Discuss and motivate!


Chapter 21: Which factors are responsible for genetic correlations between characters? How is it possible to explain the strong congruence between phenotypic and genetic correlations (Fig. 21.1) in a biologically meaningful way? How does "selection bias" influence the magnitude of genetic correlations (increasing or decreasing it)? Are there any a priori reasons to expect that genetic and phenotypic correlations should differ more for life-history traits than for morphological traits? If so, in what direction? Do we always expect trade-offs between life-history traits to be expressed as negative genetic correlations? Why? Why not?

First meeting: Chapters 1 and 4 in "Lynch & Walsh"

Our first meeting with the GENECO course will take place in the Ecology Building (Lund University) on Thursday, October 21 2010 (10.00 - 12.00). During this meeting, we will discuss chapter 1 (p. 3-17) and chapter 4 (p. 51-79). After this meeting, I expect the participants to be able to define and explain these terms:

- Homozygous effects
- Dominance coefficient
- Additive effect
- Average excess
- Breeding value
- Additive genetic variance

In particular, you should be able to explain how the link between breeding values and additive genetic variance, and how these terms are related to each other.

I also want you to discuss, in particular, the second paragraph on p. 17, about the relationship between molecular genetics and quantitative genetics. How do Lynch & Walsh counter the frequent criticism from molecular geneticists that quantitative genetics is "phenomenological", "missing the boat" or "cheating"? To what extent is it justified to ignore the details, studied by molecular geneticists, and focus on phenotypes? Do we actually need any information about mechanisms at all, to quantify and study patterns of resemblance between relatives? Would quantitative genetics work independent of the genetic material (i. e. whether it is DNA, RNA or any other self-replicating hereditary substance)? Why? Why not?

I recommend you to register your name at "Blogger" to participate in the discussion and comment on the posts below. Alternatively, you might sign with your name, but without being registered at Blogger. In any case, use this forum as a means to put forward your questions during the course.