Rupert has discovered a new eye color in Drosophila and decided to call this ext
ID: 60241 • Letter: R
Question
Rupert has discovered a new eye color in Drosophila and decided to call this extremely bright eye "hot tamale". To find out if this gene is on chromosome 2 he did a testcross of a heterozygous female to a male that is apterus (ap, chromosome 2), black (b, chromosome 2), and hot tamale (ht). The following progeny resulted Diagram this cross (using the correct gene order and coupling): identify the progeny as Parentals (P), recombinant (R), region 1 crossover (R1), region 2 crossover (R2), or double crossover (dco) as appropriate (you may not use all of these designations!) Determine the map distance between all linked genes. What gamete types would Rupert have seen if he crossed a heterozygous male to a homozygous recessive female? Use the inverse of the cross in part a as an example and be specific. Would Rupert have been able to determine if the genes are linked or unlinked if he had used the cross suggested in part d? Set up the experiment by comparing the cross in part d with a cross in which all three genes are linked and provide specific evidence.Explanation / Answer
ap + + 307 .....
+ + b 305 ..... parental progeny
ap ht + 301--------
+ ht b 300-------- single crossover progeny
ap + b 46 +++++
+ + + 41 +++++ Single cross over progeny
ap ht b 36 *******
+ ht + 34 ******* Double crossover progeny
Determination of gene order:
To identify the gene order we have to identify the middle gene because chromatids cross over twice in middle gene. In order to find middle gene parental and recombinant genotypes are compared. The parental offspring will be in large population and recombinant progeny would be smaller population.
The parental are ap + + and + + b and recombinants are ap ht b and + ht + .Here ht is the gene that is differing and switches between parental and recombinants.
So the gene order would be ap ht b or b ht ap.
calculation of map distance:
Map distance between ap and b: (47+36+41+34)/1370
= 11.4 m units
THe presence of dominant alleles on one chromosome and recessive chromosomes on other chromosome is called coupling.
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