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140
Chapter 4
•
Eukaryote Chromosome Mapping by Recombination
1000 linear asci are isolated and categorized as in the
above table. Map the
ad
and
nic
loci in relation to
centromeres and to each other.
Solution
What principles can we draw on to solve this problem?
It is a good idea to begin by doing something straightfor
ward, which is to calculate the two locustocentromere
distances. We do not know if the
ad
and the
nic
loci are
linked, but we do not need to know. The frequencies of
the M
II
patterns for each locus give the distance from lo
cus to centromere. (We can worry about whether it is
the same centromere later.)
Remember that an M
II
pattern is any pattern that is
not two blocks of four. Let’s start with the distance be
tween the
nic
locus and the centromere. All we have to
do is add the ascus types 4, 5, 6, and 7, because they are
all M
II
patterns for the
nic
locus. The total is 5
±
90
±
1
±
5
²
101 out of 1000, or 10.1 percent. In this chap
ter, we have seen that to convert this percentage into
map units, we must divide by 2, which gives 5.05 m.u.
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 Spring '08
 JOHNSON
 Biology

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