Lecture 21

Question 1

Contrast polygenic traits and monogenic traits.

Answer 1

Polygenic traits: are dependent on contributions from multiple genes

Monogenic traits: traits dependen on the contribution of a single gene(eg mendels pea plants)

Question 2

Is it possible for a monogenic trait to be quantitative? Explain your reasoning.

Answer 2

Quantative traits: are measurable traits represented by a number and are typically polygeneic traits as monogeneic traits are not measureable but rather discrete

Question 3

Is it possible for a quantitative trait to give rise to discreet variation? Explain your reasoning.

Answer 3

Quantatice traits usually do not give rise to discreet variation as they are typically polygeneic traits that give rise to measurable traits which can thus display a range of values along an uninteruppted continuom

Question 4

Define multi-factorial trait

Answer 4

There is an environmental influence as well as a genetic infleunce from multiple genes ( e.g height)

Question 5

What is the mid-parent value for a trait? Why is the mid-parent value very often an underestimate
of offspring height in humans?

Answer 5

the mid-parent value is the average of the mother and fathers trait.

Question 6

Distinguish between major and minor effect genes and how these ideas relate to the production of
different eye colors in humans.

Question 7

If a trait is determined by 5 additive genes, each with two alternative alleles, how many phenotypic
categories would be expected in the absence of an environmental effect on phenotype.

Question 8

Suppose height were determined by three genes and there was no environmental effect, and each
gene had “tall” alleles and “short” alleles. You observe and individual with a phenotype indicating the
presence of exactly 4 “tall” alleles. Can you infer their genotype? Is the same true if they had the
phenotype indicative of 6 “tall” alleles?

Question 9

Why is variation in F1s very low when parental lines that differ in a quantitative trait are crossed?

Question 10

Why does variance increase when the F1s are crossed to one another

Question 11

If the variance does not increase substantially in the F2s, is that indicative of many or few genes
underlying a trait? Explain using the Castle-Wright equation

Question 12

Define genetic liability.

Question 13

Give an example of when VG = 0. Give an example when VE = 0. Why are these cases useful?

Question 14

Which component of VG is narrow sense heritability concerned with?

Question 15

If a trait has low heritability, does that mean the trait is not determined by genes? Explain.

Question 16

Explain the method for using controlled crosses to measure broad sense heritability.

Question 17

Explain the logic of Falconer’s formula and the expectation we would have for this formula if a trait
is highly heritable.

Question 18

What are two reasons twin studies overestimate heritability?

Question 19

If R = 56 and S = 244 for a trait, calculate narrow sense heritability

Question 20

What is the expectation for R if S = 100 and h2 = 0 and why?

Question 21

What is the purpose of QTL mapping?

Question 22

Suppose you want to perform a QTL mapping study in Drosophila concerning the genes that
affect bristle number. How would you go about doing that? Assume that any parental lines you
choose have easily genotyped marker loci throughout their genome.