In chickens, sex is determined by the ZZ-ZW mechanism, where males are ZZ and females are … — JAMB UTME

In chickens, sex is determined by the ZZ-ZW mechanism, where males are ZZ and females are ZW. Barred plumage is controlled by a Z-linked dominant allele ( $Z^B$ ), whereas non-barred plumage is controlled by the recessive allele ( $Z^b$ ). A non-barred rooster ( $Z^b Z^b$ ) is mated with a barred hen ( $Z^B W$ ). If an $F_1$ male offspring is subsequently crossed with an $F_1$ female offspring, what is the probability that a female in the $F_2$ generation will have barred feathers?

A
25% (1/4)
50% (1/2)Answer
C
75% (3/4)
D
100% (1)

Answer

50% (1/2)

In the

F_1 \times F_1

cross (

Z^B Z^b \times Z^b W

), the male parent produces gametes carrying

Z^B

and

Z^b

in equal frequency (

50\%

each). Female offspring inherit the

W

chromosome from their mother and one

Z

chromosome from their father. Therefore,

50\%

of the female offspring receive

Z^B

and display barred feathers (

Z^B W

), while

50\%

receive

Z^b

and display non-barred feathers (

Z^b W

Step-by-Step Solution

Determine the genotypes of the

P_1

parents and

F_1

offspring

Parental genotypes: Male =

Z^b Z^b

, Female =

Z^B W

F_1

male genotype =

Z^B Z^b

(barred male),

F_1

female genotype =

Z^b W

(non-barred female).

The male parent passes a

Z^b

chromosome to all offspring; female offspring inherit the

W

chromosome from the mother.

Perform the Punnett square cross for the

F_1

interbreed (

Z^B Z^b \times Z^b W

)

Gametes from

F_1

male:

Z^B

Z^b

. Gametes from

F_1

female:

Z^b

W

F_2

genotypes:

Z^B Z^b

(barred male, 25%),

Z^b Z^b

(non-barred male, 25%),

Z^B W

(barred female, 25%),

Z^b W

(non-barred female, 25%).

Constructing the cross yields all possible

F_2

genotypic combinations.

Calculate the specific probability among female offspring

Female genotypes in

F_2

are

Z^B W

(barred) and

Z^b W

(non-barred) in equal proportions. Probability of barred among females =

\frac{1}{2} = 50\%

The question asks specifically for the probability within the female subset of offspring, not the total offspring.

Key Concept

ZZ-ZW Sex Determination and Sex-Linked Inheritance Ratios

Estimated Time:1m 30s

Question

Answer

Step-by-Step Solution

Key Concept

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