A multiple allelic series is known to govern the intensity of pigmentation in th

Question

A multiple allelic series is known to govern the intensity of pigmentation in the mouse such that D = full color, d = dilute color, and d^l is lethal when homozygous. The dominance order is D > d > d'^l. A full-colored mouse carrying the lethal is mated to a dilute-colored mouse also carrying the lethal. The F_1 is backcrossed to the dilute parent, (a) What phenotypic ratio is expected in the viable backcross progeny? (b) What percentage of the full-colored backcross progeny carry the lethal? (c) What fraction of the dilute-colored progeny carry the lethal?

Explanation / Answer

D = Full Color

d = dilute color

dI = lethal when homozygous

full-colored mouse carrying the lethal is mated to a dilute-colored mouse also carrying the lethal.

DdI × ddI ------- cross results 4 diffrent genotypes

Dd

(Full color)

ddI

(dilute color)

DdI

dIdI

(dead)

then make back cross to the dilute parent

mate Dd with dilute parent (ddI) you will get 4 genotypes those are - Dd (1/4), DdI (1/4), dd (1/4), ddI(1/4).

mate ddI with dilute parent (ddI) you will get 3 genotypes those are - dd(1/4), ddI(2/4), dIdI(1/4) (which is dead)

mate DdI with dilute parent (ddI) you will get 4 genotypes those are - Dd(1/4), DdI(1/4), ddI(1/4), dIdI(1/4) (which is dead).

a) what phenotypic ratio expected in the viable backcross progeny

Full colored : dilute color = 2 : 2

b) what percentage of the full-colored backcross progeny carry the lethal

so from the above calculate the percentage of progeny those have DdI genotype = (1/4)(1/4) = 1/16 = 6.25% of the full-colored backcross progeny carry the lethal

c) what fraction of the dilute colored progeny carry the lethal

from the above calculate the percentage of progeny those have ddI genotype = (1/4)(2/4)(1/4) = 2/64

D dI d

Dd

(Full color)

ddI

(dilute color)

dI

DdI

dIdI

(dead)

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