2. A Northern Ontario Geneticist is mapping genes in Procyon lotor, also known a
ID: 171361 • Letter: 2
Question
2. A Northern Ontario Geneticist is mapping genes in Procyon lotor, also known as the common raccoon. She takes raccoon females heterozygous for each of three autosomal recessive mutations (red fur [a], no rings around eyes [b], and absence of striped tail [c]), and testcrosses them to males showing all three mutant phenotypes producing 1000 progeny of the following phenotype: red hair, no ring, no stripe 432 WT 429 red hair, no ring 37 red hair, no stripe 35 no ring 34 no stripe 33 A] Show the arrangement/order of alleles in the heterozygous trihybrid female parent (1 mark). B] Draw the genetic map that explains the obtained data (2 marks) C] Show whether or not Interference is occurring (2 marks)?
Explanation / Answer
Three autosomal recessive mutations:
red fur a
no rings around eyes b
absence of stripped tail c
A female heterozygous for three genes, A/a B/b C/c is test crossed to males showing all three mutant phenotypes a/a b/b c/c.
1000 progeny obtained after gametic contribution of the heterozygous parent are classified as follows:
A . B . C 429
a . b . c 432
a . B . c 35
A . b . c 37
a . b . C 34
A . B . c 33
Total = 1000
Possible gene order;
To calculate the recombination frequency we have to take into account the recombination products;
From the list we note that there are: 35 + 37 + 34 +33 of these types;
Therefore Recombination Frequency = (139/1000) × 100 = 13.9 m.u.
Interference is the tendency of crossing over between two pairs of genes inorder to reduce the chance of crossing over of one of those genes with a different gene.
It is calculated by subtracting a ratio of observed crossing over frequency to the expected crossing over frequency from 1.
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