Below is diagramed the pathway for pigment development in the chicken. In words,

Question

Below is diagramed the pathway for pigment development in the chicken. In words, the autosomal dominant allele C produces an enzyme that converts the colorless substrate, s, to the colored pigment, p. The recessive allele c produces an inactive enzyme. The Zlinked, dominant allele A produces an inhibitor production. Colorless precursor -----------------> Yellow Pigment a) If you crossed a white hen of genotype Z^A WCC with a white cock of genotype Zd Zd cc what would be the phenotype and genotype of the F1? b) If you crossed the F1 chickens among themselves, what would be the phenotype ration of the F2?

Explanation / Answer

Answer.

Given,
Genotype with
SS = produces Enzyme for Colored Pigmentation
Ss or sS = produces Enzyme for Colored Pigmentation
ss = produces Inactive Enzyme (will be White)

ZAW = produces Inhibitor to inhibit the action of Enzyme
ZaW = No Inhibitor
ZAZA = produces Inhibitor to inhibit the action of Enzyme
ZAZa orZaZA = produces Inhibitor to inhibit the action of Enzyme
ZaZa = No Inhibitor

Ans a.

In Female Birds, only 1 Z chromosome
and in Male Birds, 2 Z chromosomes

Now given White Hen ( ZAW CC)
produces gametes,
( ZAC, WC )
and White Cock (ZaZa cc)
produces gametes,
(Zac)

On Cross,
ZAC x   Zac = ZAZa Cc (Male, White)
Dominant allele A produces Inhibitor and no Pigment produced
WC  x   Zac = WZa Cc (Female, Colored)
Recessive allele a doesn't produces Inhibitor and Pigment is produced

Ans. b
In F2 gen.,
The F1 gen produces,
ZAZa Cc
produces gametes, = (ZAC, Za C, ZAc, Zac)
and,
WZa Cc
produces gametes, = (WC, Wc, ZaC, Zac)

On Cross,
ZAC x WC = ZAW CC (Female,White)
Za C  x WC =  ZaW CC (Female,Colored)
ZAc  x WC = ZAW Cc   (Female,White)
Zac  x WC =   ZaW Cc   (Female,colored)

ZAC x Wc = ZAW Cc   (Female,White)
Za C  x Wc =  ZaW Cc   (Female,Colored)
ZAc  x Wc = ZAW cc (Female,White)
Zac  x Wc =   ZaW cc (Female,White)

ZAC x ZaC = ZAZa CC   (Male,White)
Za C  x ZaC =  ZaZa CC   (Male,Colored)
ZAc  x ZaC = ZAZa Cc (Male,White)
Zac  x ZaC =   ZaZa Cc (Male,Colored)

ZAC x Zac = ZAZa Cc (Male,White)
Za C  x Zac =  ZaZa Cc (Male,Colored)
ZAc  x Zac = ZAZa cc   (Male,White)
Zac  x Zac =   ZaZa cc   (Male,White)

Threfore,
in F2 gen, 10 White Birds : 6 Colored Birds
In Hen,
5 White : 3 Colored
In Cock,
5 White : 3 Colored

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