A farmer who raises rabbits wants to break into the seasonal Easter market. He h

Question

A farmer who raises rabbits wants to break into the seasonal Easter market. He has stocks of two true-breeding lines. One is hollow, and long-eared but not chocolate (hh lele ChCh), while the second is solid, short-eared, and chocolate (HH LeLe chch). Hollow (h), long ears (le), and chocolate (ch) are all recessive, autosomal, and linked as in the following map: The farmer can generate a trihybrid by crossing his two lines; the trihybrids represent the F_1 generation. At great expense he is able to obtain the services of a male rabbit homozygous recessive at all three genes to cross with his F_1, females The farmer has buyers for both solid and hollow bunnies; however, all must be chocolate (of course) and long eared. Assuming that interference is zero, calculate the percentage of the total F_2 progeny that will be the desired phenotypes (solid, long-eared, chocolate or hollow, long-eared, chocolate).

Explanation / Answer

The parent stocks will have the following genotypes:

Parent: hh lele ChCh and HH LeLe chch

Now the cross between these two will give F1 as follows:

F1: H_Le_ch/h_le_Ch

A homozygous recessive male will have the genotype h_le_ch. Assuming 0 interference if cross is done between F1 and the homozygous male then the genotypes, phenotypes and their percentages will be as follows:

h_le_Ch/h_le_ch - hollow, long ears and chocolate- 27%

H_Le_ch/h_le_ch - solid short ears and not chocolate - 27%

H_le_Ch/h_le_ch- solid long ears and chocolate- 6.8%

h_Le_ch/h_le_ch- hollow not chocolate short ear- 6.8%

h_le_ch/h_le_ch- hollow not chocolate long ear- 12.8%

H_Le_Ch/h_le_ch- solid chocolate short ear- 12.8%

h_Le_Ch/h_le_ch- hollow short ear chocolate- 3.2% and

H_le_ch/h_le_ch- solid not chocolate long ears- 3.2%

Due to the distance of 26mu and 32 mu between h and le, le and ch respectively, the double recombinant frequency will be 0.32X0.26=0.083. So the percentage of double recombinants will be 8.3%. Frequency of SCO between h and le will be 8.3%. Frequency of parentals will be 54%. The percentage of short ears and chocolate in F2 will be 27+8.3= 35.3%. The breeder should continue with the breeding as around 35.3% of progeny will be of desired phenotype.

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