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Evolution: The Molecular Landscape

Cold Spring Harbor’s 74th Symposium
The Molecular Landscape
Edited by Bruce Stillman,
David Stewart, and
Jan Witkowski,
Cold Spring Harbor Laboratory


Evolution Chapter 14 Discussion Questions

DQ 14.1

Does it make sense to say that the DNA sequence determines the organism?

DQ 14.2

Geneticists are often said to find a gene responsible for a complex trait, as the quotes below show. What exactly is meant by a gene “for” a trait?

“‘Fat’ gene found by scientists” (The Times, April 13, 2007)

“Twins hold key to unravelling maths gene” (Guardian, August 7, 2005)

“Evidence for homosexuality gene: a genetic analysis of 40 pairs of homosexual brothers has uncovered a region on the X chromosome that appears to contain a gene or genes for homosexuality” (Science, July 16, 1993)

DQ 14.3

Often, we think of a simple quantitative trait such as the height of a human, the weight of a plant’s seeds, or the number of bristles on a fly. However, real phenotypes, taken as a whole, are far more complex: Think of the shape of an insect’s wing, the pattern of growth (i.e., body size through time), the chance of survival with increasing age, or crop yield as a function of amount of fertilizer. Explain how these kinds of trait can be described by quantitative genetics.

DQ 14.4

What is meant by a “variance component”?

DQ 14.5

Organisms function through an immensely complex network of interactions between multiple genes (e.g., Fig. 14.1). Why, then, can a simple additive model be used to describe variation in genetically complex traits?

DQ 14.6

Figure 14.15 shows estimates of the heritability of mental abilities, based on a study of twins. What does knowing that the heritability is about 50% tell us?

DQ 14.7

The first quantitative trait locus was mapped nearly a century ago (Payne 1918). Why, then, has QTL mapping only recently become widely used?

DQ 14.8

Why is it so difficult to find the precise variant that contributes to variation in a trait? (This problem is sometimes referred to as finding the QTN, or “quantitative trait nucleotide.”)


Payne F. 1918. The effect of artificial selection on bristle number on Drosophila ampelophila and its interpretation. Proc. Natl. Acad. Sci. 4: 55–58. NOTE 14A


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