In fruit flies (*Drosophila melanogaster*), the allele for normal wings (V) is completely … — JAMB UTME

In fruit flies (*Drosophila melanogaster*), the allele for normal wings ( $V$ ) is completely dominant over the allele for vestigial wings ( $v$ ). Match each parental cross listed on the left with its corresponding expected offspring phenotypic or genotypic ratio on the right.

Cross between two heterozygous normal-winged flies ( $Vv \times Vv$ )3 : 1 phenotypic ratio of normal wings to vestigial wings
Test cross of a heterozygous normal-winged fly ( $Vv \times vv$ )1 : 1 phenotypic ratio of normal wings to vestigial wings
Cross between a homozygous normal-winged fly and a vestigial-winged fly ( $VV \times vv$ )100% normal wings (all offspring are heterozygous $Vv$ )
Cross between a homozygous normal-winged fly and a heterozygous fly ( $VV \times Vv$ )100% normal wings (1 : 1 genotypic ratio of $VV$ to $Vv$ )

Answer

Cross

Vv \times Vv

matches 3:1 phenotypic ratio (normal:vestigial). Test cross

Vv \times vv

matches 1:1 phenotypic ratio. Cross

VV \times vv

matches 100% normal wings (all

Vv

). Cross

VV \times Vv

matches 100% normal wings (1:1 genotypic ratio

VV:Vv

Each monohybrid cross yields specific offspring ratios according to Mendel's Law of Segregation. Crossing two heterozygotes (

Vv \times Vv

) yields a 3:1 phenotypic ratio. A test cross (

Vv \times vv

) yields a 1:1 phenotypic ratio. Crossing homozygous dominant with homozygous recessive (

VV \times vv

) produces 100% heterozygous offspring (

Vv

). Crossing homozygous dominant with a heterozygote (

VV \times Vv

) yields 100% dominant phenotype with a 1:1 genotypic ratio of

VV

Vv

Step-by-Step Solution

Analyze the cross

Vv \times Vv

Produces genotypes

1\ VV : 2\ Vv : 1\ vv

. Since

V

is dominant, 3 parts show normal wings and 1 part shows vestigial wings (3:1 phenotypic ratio).

Mendel's Law of Segregation states that two alleles of a gene separate during gamete formation.

Analyze the test cross

Vv \times vv

Gametes from

Vv

are

V

and

v

; gametes from

vv

are

v

. Offspring are 50%

Vv

and 50%

vv

(1:1 phenotypic ratio).

A monohybrid test cross pairs a heterozygous individual with a homozygous recessive individual.

Analyze the cross

VV \times vv

All offspring inherit

V

from the dominant parent and

v

from the recessive parent, resulting in 100%

Vv

(100% normal wings).

Homozygous dominant crossed with homozygous recessive produces uniformly heterozygous F1 offspring.

Analyze the cross

VV \times Vv

Offspring genotypes are 50%

VV

and 50%

Vv

. Because all possess at least one dominant allele

V

, 100% display normal wings.

The dominant allele masks the recessive allele in heterozygous individuals.

Key Concept

Mendel's First Law and Monohybrid Inheritance Ratios

Question

Answer

Step-by-Step Solution

Key Concept

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