2. In rabbits, black (B) is dominant to brown (b) and full-color (F) is dominant

Question

2. In rabbits, black (B) is dominant to brown (b) and full-color (F) is dominant to chinchilla (f). Individuals heterozygous for both traits were crossed to brown, chinchilla rabbits (bb ff). The following offspring resulted 31 brown, chinchilla 34 black, full-color 16 brown, full-color 19 black, chinchilla Write the chromosome structure of the F1 heterozygote as they would appear on chromosomes. Is the chromosome structure in cis a. (coupling) or trans (repulsion)? b. What is the map distance between the B and C genes? Are they completely linked, incompletely linked or not linked? Several more two point crosses were performed and the following recombination frequencies were obtained C. B- F E- B (results calculated above) 5% 39% 50% 16% D -E F- D d. Draw a map of the genes, with the distances between each gene marked in map units or centiMorgans. e. How many map units apart are the D and E genes?

Explanation / Answer

Answer:

a). bF/Bf (F1 heterozygote)

The chromosomes are in trans (repulsion)

b).

RF =( 35 / 100) 100 = 35%

RF = Map distance

So the distance between B and C genes = 35 map units.

The genes are incompletely linked. If they are in complete linkage, there would not be any recombinants. Less number of recombinants are produced means that they are in incomplete linkage.

c&d).

D—16cM---F-----35cM-----B---5cM---E

e). The map units distance between gene D & E = 50 mu (as RF(%) = mu)

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