Biology Reference
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blocks of DNA. h e cuts allow DNA repair or transcription (the pro-
duction of a translated copy of the DNA sequence of a gene that can be
used by the cell to make a protein or peptide) to take place. h ere are
many dif erent enzymes that recognize many dif erent sequences (cut
sites) scattered throughout the genome. Every individual has a unique
set of cut sites due to random mutations and the sequences inherited
from his or her parents. If you take the DNA of a single individual and
digest it with a specii c restriction enzyme, the DNA will be cut into
many pieces of varying length, depending on where the cut sites are
located and the mutational history of the DNA segments they l ank.
h e digested DNA can then be run on a gel slab that separates the pieces
according to size, and they can be stained so you can see them. h e
pattern observed gives information that can be used for mapping the
locations of the individual fragments in the genome. Greg wanted to
make a restriction site map of the honey bee.
Very little mapping had been done with honey bees. Before the de-
velopment of DNA markers, genetic mapping was done with visible
mutations. h e fruit l y Drosophila had an extensive map of muta-
tions on chromosomes because of the large number of known visible
mutations and the large, stainable polytene chromosomes found in its
salivary glands. Even though instrumental insemination had made
the honey bee the model for studying social insect genetics, there
were few visible genetic markers and, therefore, only a few “linkage
groups” known, mostly the work of Harry Laidlaw and his colleagues.
When I let h e Ohio State University, I went with the intention of
mapping the sex locus (see Chapter 4) once I was established at the
University of California-Davis. Hunt's phone call could not have
been timed better.
Hunt was admitted to graduate school and joined my lab in 1989.
About the same time, an article by a group of plant geneticists, some of
whom were at UC Davis, appeared in the journal Nature. h ey con-
structed a genetic map of quantitative trait loci (QTLs) for phenotypic
traits that had been bred in tomatoes. QTLs are genes that explain dif-
ferences in phenotypes that must be measured (see Section 4.4.1.2). h e
tomato map was one of the i rst QTL maps done by genetically map-
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