Population Genetics Problem #3

Theodosius Dobzhansky studied many different problems using the inversion types of Drosophila pseudoobscura as a genetic marker. In one experiment, he set up a population of 2500 flies, 2000 were female and 500 were male. The genotype counts in this population were:¹

	Inversion genotype
	$ST/ST$	$ST/CH$	$CH/CH$
Females	263	917	820
Males	73	231	196
Total	336	1148	1016

From this base population, he constructed a series of 50 replicate populations by sampling eggs at random into populations of 2500 individuals each, producing the following vector of counts of $ST$ chromosomes (data in WinBUGS format):

list(k=c(2081, 2137, 1655, 1733, 2164, 1723, 2078, 1783, 1677, 1982,
   2007, 1861, 1667, 1324, 1556, 1934, 1914, 1788, 2397, 1882, 1429,
   1882, 1862, 1796, 1739, 1583, 1402, 2014, 1978, 1809, 1542, 2008,
   1508, 2035, 1705, 1512, 2183, 2301, 1932, 1860, 1653, 1751, 1587, 
   1535, 1593, 1984, 1873, 1948, 1689, 1674))

Using these data answer the following questions:

1. Is there evidence for a difference in the frequency of the $ST$ in females and males?

2. What is the estimated variance effective size of the base population?

3. Is the estimated variance effective size consistent with what would be predicted from the known numbers of males and females in the base population?

4. What evolutionary process could account for any discrepancy between estimated and predicted variance effective sizes?²