Linkage problems

1
Linkage problems
2
You obtained a dihybrid individual of genotype
AaBb. Genes A and B are linked. In order to
determine the allelic phase in the dihybrid you
perform a test cross with the following
outcome 45 aaBb 45 Aabb 5 AaBb 5 aabb

• Answer
• The alleles are in coupling
• The alleles are in repulsion
• It is not possible to tell the phase
• The two genes assort independently

b. Is the correct answer
3
Drosophila Recessive autosomal traits
crossveinless (cv), echinus (ec), and cut wing
(ct). A test cross is performed between a
trihybrid female with the wild type phenotype and
a male with the three recessive phenotypes. The
following progeny are obtained
4

• (wwhite eyes, yyellow body, mminiature wings)
• P1 ww yy mm ? x P2 wild type ?
• F1 550 wild type ? 545 triple mutant ?.
• How do you explain the difference in phenotypes
  between males and females?
• Answers
• The 3 genes are autosomal
• The three genes are X-linked
• Females are unable to express mutant phenotype
• None of the above

b. Is correct
5
P1 ww yy mm ? x P2 wild type ? A F1 ? is
backcrossed to the wild type ? parent Results
? 6004 wild type ? 5943 2277 wild type
6 white eyes 643 miniature wings
50 white eye, min wings 52 yellow 654
white eye, yellow 8 yellow, min wing
2253 white, yellow, min What is the alleleic
phase for w and m a. coupling b. repulsion
c. both
a. Is correct
6

• P1 ww yy mm ? x P2 wild type ?
• A F1 ? is backcrossed to the wild type ? parent.
• Results
• ? 6004 wild type
• ? 1) 2277 wild type
• 2) 6 white eyes
• 3) 643 miniature wings
• 4) 50 white eye, min wings
• 5) 52 yellow
• 6) 654 white eye, yellow
• 7) 8 yellow, min wing
• 8) 2253 white, yellow, min
• Which gene is in the middle?
• m
• w
• y

b. Is correct