Biology Reference
In-Depth Information
Imagine that there are p sex alleles in a population, each at equal
frequency. h en the frequency of each will be 1/ p at equilibrium. What
is the probability that a queen will mate with a male having a sex allele
identical to one of hers? She has two dif erent alleles, so for each male
with which she mates, the chance that he will have one like hers is 2/ p.
For example, if there are 10 sex alleles in the population, each at a fre-
quency of 0.10 (10 percent), then she has a 20 percent likelihood
(2 × 0.1 = 0.20) of mating with a male that has an allele like one of hers
every time she mates. So, on average 20 percent of the males she mates
with will have a matching allele. If she mates with 10 males, on average
two will have an allele that matches hers. Half of the of spring derived
from those two males will be diploid males and will not survive. h e
average proportion of diploid larvae produced by that queen will be
0.20 (the proportion of males with matching alleles) × 0.50 (the propor-
tion of the of spring of that male that will be homozygous; remember
that the queen has two dif erent alleles) = 0.10. Her expected brood vi-
ability then is 0.90 or 90 percent.
If queens in a population mate just one time, then there will be only
two classes of queens, those that produce 50 percent diploid males (50
percent viable brood) from their fertilized eggs and those that produce
none (100 percent viable brood). If there are 10 sex alleles at equal fre-
quency, then 80 percent of the queens will have 100 percent brood via-
bility, and 20 percent will have 50 percent. If a queen mates a very large
number of times, then the representation of sex alleles in her sperma-
theca, which are derived from her mates, will get very close to that of
the whole population. So, a queen that mates with a very large number
of males in our population with 10 sex alleles will have 20 percent of the
sperm in her spermatheca with sex alleles that match an allele in the
eggs she produces, resulting in diploid males. In this case all queens that
mate this very large number of times will have the same brood viability,
90 percent. You can see that the number of times a queen mates
af ects the distribution of brood viability among queens in a popula-
tion (Figure 4.3). But you can also see that the average brood viability
for all queens in a population remains the same regardless of the number
of times queens mate. In our example population with single mating, the
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