Question

Please show all work step by step!! Please don't just give me answers.Thank you.

In whales, the gene controlling tail shape exists as a dominant notched (T) or a recessive smooth (t) allelic form. A separate gene controls whether there are white markings on the dorsal fin or not. The dominant allele of the second gene (W) results in no white markings whereas the other allele (w) results in white markings in individuals homozygous for the recessive allele. The T and W genes are linked together and are 20 map units apart. A purebreeding female with a notched tail and white markings on her dorsal fin mates with a purebreeding male with a smooth tail and no white markings on his dorsal fin. One of the F1 females resulting from this cross mates with a homozygous recessive male.

-Draw out the genotypes of the parents of the original cross on chromosomes (the purebreeding parents)

-Draw out the genotypes of the F1 heterozygote female resulting from the cross in part a and the homozygous recessive male (you do not need to include the sex chromosomes).

-What proportion (%) of the progeny from the cross in (b) would express each of the following phenotypes?

Notched tail, white markings on dorsal fin _____________

Notched tail, no white markings on dorsal fin _____________

Smooth tail, white markings on dorsal fin _____________

Smooth tail, no white markings on dorsal fin _____________

Answer 1

Answer:

A purebreeding female with a notched tail and white markings on her dorsal fin = Tw/Tw

A purebreeding male with a smooth tail and no white markings on his dorsal fin = tW/tW

Tw/Tw x tW/tW –Parents

Tw/tW -------------F1

Tw/tW (F1 female) x tw/tw (tester male) ---Testcross

Distance between genes (mu) = Recombination frequency (%)

20 mu = 20%

Tw/tW genotype produces 4 types of gametes as below:

Recombinant gametes (20%):

TW = 10%

tw = 10%

Non-recombinant gametes (80%):

Tw = 40%

tW = 40%

tw/tw genotype produces only one type of gamete, tw.

Hence, the propotion of each phenotype is determined by the gametes produced by F1 female.

Notched tail, white markings on dorsal fin = Tw = 40%

Notched tail, no white markings on dorsal fin = TW = 10%

Smooth tail, white markings on dorsal fin = tw = 10%

Smooth tail, no white markings on dorsal fin = tW = 40%