Question

In cats, the Dense pigment gene, D/d, codes for melanophilin, a protein involved in the transportation and deposition of pigment into a growing hair. A separate gene, M/m, is responsible for the production of the pigment, with M_ producing black pigment and mm producing brown. When a cat has two recessive d alleles, its fur is a light gray color regardless of which alleles of M/m are present.
Required:
State the phenotype and frequency for each of the following outcomes of a dihybrid cross:

a. M_D_
b. M__dd
c. mmD
d. mmdd

Answer 1

Answer:

a. M_D_ : 9/16 Black furred individuals

b. M__dd : 3/16 gray furred individuals (1/16 MMdd + 2/16 Mmdd)

c. mmD_ : 3/16 Brow-furred individuals (1/16 mmDD + 2/16 mmDd)

d. mmdd: 1/16 gray furred individuals.

Explanation:

Available data:

• Dense pigment gene, D, codes for melanophilin.
• D allele dominant over d.
• Gene M/m is responsible for the production of the pigment
• M is dominant over m
• If D is present, M/m is expressed
• If dd is present, M/m is not expressed  
• DDMM, DdMM, DDMm, DdMm --->Black fur
• DDmm, Ddmm ---> Brown fur
• ddMM, ddMm -----> Light gray fur

Cross: between two dihybrids

Parental)         DdMm     x     DdMm

Phenotype) Black-furred      Black-furred

Gametes) DM, Dm, dM, dm   DM, Dm, dM, dm

Punnet Square)    DM        Dm         dM          dm

             DM       DDMM    DDMm   DdMM   DdMm

             Dm       DDMm    DDmm   DdMm   Ddmm

             dM        DdMM    DdMm    ddMM   ddMm

             dm        DdMm    Ddmm    ddMm   ddmm

F1) 9/16 Black-furred individuals, D-M- (1/16 DDMM + 2/16 DDMm + 2/16    

                                                                 DdMM + 4/16 DdMm)

    3/16 Brown-furred individuals, D-mm ( 1/16 DDmm + 2/16 Ddmm)

    4/16 Gray-furred individuals, dd-- ( 1/16ddMM + 1/16 ddmm + 2/16 ddMm)