Biology Reference
In-Depth Information
same number of linkage groups as chromosomes. h is was already an
enormous ef ort. To construct the map, we set up and ran about 30,000
individual polymerase chain reactions, a task that took more than two
years.
6.2.2 Mapping QTLs
h e next step was to map QTLs for pollen hoarding. Our map was suf-
i ciently saturated even though our linkage groups did not coalesce
into 16 chromosomes. We had a marker on average every 10cM, mean-
ing that we had an average probability of recombination between our
markers of 10 percent. But we needed phenotypes to assign to the ge-
nomes that constituted the map.
Males that were used for the map were also fathers of colonies
(Figure 6.2). Males were randomly selected to provide sperm for instru-
mental insemination of high-strain queens. Before we ground them up
to take their DNA, we ejaculated them and collected their sperm. h e
queens were super sisters, derived from the same mother who had been
inseminated with the semen of a single drone. h is is known as a high-
strain backcross. We crossed the hybrid drones to high-strain queens
because we had already shown that the pollen-hoarding trait, as well as
individual foraging behavior and many other trait dif erences between
highs and lows, shows directional dominance for the low-strain pheno-
type. In hybrid crosses, the expressed phenotypes are ot en more like
the low strain, not intermediate in value (Figure 5.7). A backcross to a
low-strain queen is not likely to show sui cient variation in phenotype
to map the QTLs. It is like the inheritance of eye color. Genes (alleles) for
blue eyes are recessive to the dominant brown eyes. An individual that
inherits a gene for brown eyes from one parent and blue eyes from the
other will still have brown eyes. If one parent has two alleles for blue
eyes (one inherited from each parent) and the other parent has two
brown alleles, all of their children will have one allele of each, and,
therefore, all will have brown eyes—no phenotypic variation.
h e high-strain queens that were inseminated with the sperm from
the hybrid drones were placed in colonies where they laid eggs, and at er
