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Unformatted text preview: Worked problems:
Question 1:
Genes a and b are linked, with 10% recombination. What would be the phenotypes,
and the probability of each, among progeny of the following cross?
a b+
a+ b X ab
ab recombinants:
a b / a b : 10% / 2 = 5%
a+ b+ / a b b : 10% / 2 = 5%
parentals:
a b+ / a b : 90% / 2 = 45%
a+ b / a b : 90% / 2 = 45% Question 2:
Genes a and b are seclinked and are located 7 mu apart on the Xchromosome of
Drosophila. A female of genotype a+ b / a b+ is mated with a wildtype male (a+ b+/
Y).
a) What is the probability that her sons will be a+ b+ in phenotype?
b) What is the probability that her daughters will be a+ b+ in phenotype?
a) a+ b+ / Y = recombinant; frequency = 7% / 2 = 3.5%
b) a+ b+/ any genotype from mother ; 100% a+ b + phenotype
Question 3:
In corn, the allele for coloured (C) seeds is dominant to the allele for colourless (c).
A gene controlling endosperm development shows a similar relationship, Full (S) is
dominant to shrunken (s). You are not sure what the parental phenotypes were,
but you have the following F1 progeny:
Coloured, full
4 032
Coloured, shrunken
149
Colouless, full
152
Colourless, shrunken
4 035
Total
8 368 Are these genes linked? If so, construct a linkage map.
Yes; 3.6 mu between c and s Question 4.
A corn plant known to be heterozygous at three loci is testcrossed. The progeny
phenotypes and numbers are as follows:
+++
abc
+b c
a ++
++c
ab+
+b+
a+c 455
470
35
33
37
35
460
475 Give the gene arrangement, linkage relationships, and map distances.
b is sorting independently of a and c, that is why we see a c with b or b+ with
equal frequency i.e. a c b and a c + with equal frequency, + + b and + + + with
equal frequency. (RF=50% between b and a and b and c)
Recombinants between a and c = 140/1860 = 7.5% a  7.5mu  c
b on a different chromosome or very far away on the same chromosome. ...
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This note was uploaded on 06/09/2011 for the course BIOLOGY 2c03 taught by Professor Dej during the Spring '11 term at McMaster University.
 Spring '11
 Dej
 Genetics

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