MC

c2b0_663a

Gene 1
blue ⟶ sky blue
Only Gene 1 Dominant
Gene 2
blue ⟶ tan
Only Gene 2 Dominant
Genes 1+2
blue ⟶⟶ white
Both Genes Dominant

A two step metabolic pathway determines the pigment color. Gene 1 when dominant expresses an enzyme that creates the sky blue pigment from the blue precursor pigment. Gene 2 when dominant expresses an enzyme that creates the tan pigment from the blue precursor pigment. When both genes are dominant, the two enzymes pathways combine to form the new white pigment. If neither of the genes are dominant, then there is no pigment change and the blue precursor pigment remains.

The diagram and description above explain the interaction of two genes. Determine the dihybird cross phenotypic ratio.

A.

These two genes would show duplicate dominant epistasis and a 15:1 ratio.

duplicate dominant epistasis Female ♀
AT At aT at
Male
♂		 AT AATT AATt AaTT AaTt
At AATt AAtt AaTt Aatt
aT AaTT AaTt aaTT aaTt
at AaTt Aatt aaTt aatt
Incorrect B.

These two genes would show recessive epistasis and a 9:3:4 ratio.

recessive epistasis Female ♀
AT At aT at
Male
♂		 AT AATT AATt AaTT AaTt
At AATt AAtt AaTt Aatt
aT AaTT AaTt aaTT aaTt
at AaTt Aatt aaTt aatt
Incorrect C.

These two genes would show monohybrid epistasis and a 12:4 ratio.

monohybrid epistasis Female ♀
AT At aT at
Male
♂		 AT AATT AATt AaTT AaTt
At AATt AAtt AaTt Aatt
aT AaTT AaTt aaTT aaTt
at AaTt Aatt aaTt aatt
Incorrect D.

These two genes would show digenic inheritance and a 9:3:3:1 ratio.

digenic inheritance Female ♀
AT At aT at
Male
♂		 AT AATT AATt AaTT AaTt
At AATt AAtt AaTt Aatt
aT AaTT AaTt aaTT aaTt
at AaTt Aatt aaTt aatt
Correct