Evolutionary Genetics: Exercises in Quantitative Genetics
HS2013
Name:_________________________
Mathias Kölliker & Janine Wong
Matrikel-Nummer:_______________________
SESSION 4: HALF‐SIB BREEDING DESIGN
OVERVIEW
An important question in studies of sexual selection is whether or not females can benefit from
mating with attractive males by producing attractive sons. The potential for any indirect genetic
benefits therefore depends on the resemblance between father and son. Using quantitative genetic
approaches we look at these questions by estimating the heritability of traits related to mating
success in males.
Today’s data comes from a quantitative genetic study on the black field cricket (Teleogryllus
commodus) where two measures of male attractiveness were made: 1) how quickly a male takes to
mate with a random female (the inverse of latency to mate), and 2) how much time a male spends
calling each night to attract potential mates (average calling in minutes per night).
This study used a nested full‐sib, half‐sib breeding design where 35 males were each mated to four
females. The two estimates of attractiveness were then measured for three males per family. Based
on this design we can use the amount of phenotypic resemblance among relatives to provide an
indication of the underlying genetic variation for the two attractiveness traits.
LEFT: A mating pair of the Australian black field cricket. RIGHT: The standard full‐sib/half‐sib
breeding design used in the experiment, where each male (sire) was mated to four females (dams).
A total of three males were then measured from each family.
Evolutionary Genetics: Exercises in Quantitative Genetics
HS2013
Mathias Kölliker & Janine Wong
PART 1: CALCULATING HERITABILITIES
Summary of a balanced nested analysis of variance involving s sires, d dams per sire and k offspring
per dam. sdk is the total number of sibs in the design.
A worked exmaple of a nested design. Suppose s = 10 sires are crossed to d = 3 dames and k = 10
offspring measured in each full‐sin family, with resulting ANOVA table.
P
Evolutionary Genetics: Exercises in Quantitative Genetics
HS2013
Mathias Kölliker & Janine Wong
PRACTICAL 1: Calculate the variance components from the nested half‐sib analyses of latency to
mate and time spent calling. Then calculate the dam and sire heritabilities.
How quickly mating occurs („latency“)
Factor
df
MS
Variance Comp.
Sire
σ2S =
Dam(Sire)
σ2D =
Within Dams
σ2W =
Heritability
Time spent calling each night
Factor
df
MS
Variance Comp.
Sire
σ2S =
Dam(Sire)
σ2D =
Within Dams
σ2W =
Heritability
QUESTION 1: What do the sire heritabilities tell you about the underlying causes of phenotypic
variation for the above traits?
QUESTION 2: How do the dam heritabilities compare to those estimate based on sire only effects?
QUESTION 3: Name one genetic and one environmental component that could inflate the dam
heritabilities.
QUESTION 4: Do you think it is possible that females could gain indirect genetic benefits from
mating with attractive males? How strong would such benefits, if any, be? Explain briefly.