Biology Reference
In-Depth Information
He was able to rear the newly hatched larvae in the laboratory for their
i rst 72 hours of life and return them to their cells, where the nurse bees
cared for them as if they were normal. He produced adult diploid males
and showed that they were ef ectively sterile—evolutionary dead ends.
h en over a period of 13 years (from 1990 to 2003) the
csd
gene was gene-
tically mapped, isolated, and sequenced, and its complementary mode of
action was coni rmed by students and postdocs in my laboratory and the
laboratory of my former postdoc, Martin Beye.
4.2.2 Population Genetics of Sex Determination
Homozygosity at the sex locus results in the death of larvae due to sibi-
cide, sisters killing sisters in this case. So how common is homozygos-
ity? h e population genetics of
csd
have been carefully explored. Honey
bee populations have between 6 and 18 sex alleles that are functionally
complementary, depending on the population measured. h e number
of sex alleles is a consequence of selection-mutation-drit equilibrium.
New alleles arise through mutation, a random change in the DNA se-
quence associated with the region of the gene responsible for comple-
mentarity. Beye and members of his lab have been characterizing the
nature of the alleles and the kinds of mutations that can occur and be
compatible with other alleles. h e fate of most new mutational variants
of most genes is to be eliminated from the population soon at er they
occur because they reduce the survival and reproductive success of
their owners or are lost to genetic drit .
Ge ne tic drit is simply sampling error. Imagine that you have a bowl
with 100 randomly mixed marbles. Half the marbles are blue; the others
are red. You draw exactly 4 marbles from the bowl. h e chances are
that frequently you will not get exactly 2 of each color. Let us say that
you get 3 of one color and 1 of the other, an occurrence with relatively
high expectation (50 percent chance). In this case, let us make it 3 reds
and 1 blue. You empty the bowl and now i ll it with the proportional
colors that you drew, the same as if each marble made 25 new copies of
itself to go into the bowl. Now the bowl has 75 reds and 25 blues. h e
proportion of reds and blues has drit ed. h e next time you draw 4, the
