X-linked genetic question

Question

Drosophila, vestigial wings (vg) is a recessive autosomal mutant allele, and yellow body (y) is a recessive X-linked mutant allele. The wild-type alleles, vg+ and y+ control normal wings and dark-brown body colour respectively. If a homozygous yellow, vestigial female is crossed to a normal male and the F1 offspring are interbred, what will be the phenotypes and ratios of the F1 and F2 ?

Answer 1

Parental Genotypes:

* Female (homozygous mutant):

* Autosomes: vg/vg (vestigial wings)

* Sex chromosomes: Xʸ/Xʸ (yellow body)

* Male (wild type):

* Autosomes: vg+/vg+ (normal wings)

* Sex chromosomes: Xʸ⁺/Y (normal body)

X-Linked (Sex-linked) Trait: Yellow Body

| Xʸ⁺ (from father) | Y (from father)

-------------- |------------------------|--------------------

Xʸ (from mother) | Xʸ⁺/Xʸ (♀) – normal | Xʸ/Y (♂) – yellow

Xʸ (from mother) | Xʸ⁺/Xʸ (♀) – normal | Xʸ/Y (♂) – yellow

Results:

Female offspring: Xʸ⁺/Xʸ → normal body (carriers)

Male offspring: Xʸ/Y → yellow body (affected)

Autosomal Trait: Vestigial Wings

| vg⁺ (from father) | vg (from father)

-------------- |-------------------|------------------

vg (from mother) | vg⁺/vg | vg⁺/vg

vg (from mother) | vg⁺/vg | vg⁺/vg

All offspring: vg⁺/vg → normal wings (carriers)

Combined F1 summary: The cross between a homozygous yellow, vestigial female (Xʸ/Xʸ; vg/vg) and a normal male (Xʸ⁺/Y; vg⁺/vg⁺) produces F1 offspring with the following phenotypes: 50% females with normal body color and normal wings (Xʸ⁺/Xʸ; vg⁺/vg)and 50% males with yellow body color and normal wings (Xʸ/Y; vg⁺/vg). All offspring are heterozygous for the autosomal wing gene (vg⁺/vg), resulting in normal wings.

F2 Generation (F1 ♀ × F1 ♂)

Now cross the F1 female (Xʸ⁺/Xʸ ; vg⁺/vg) × F1 male (Xʸ/Y ; vg⁺/vg)

Gametes:

1. Female produces:
2. Sex: Xʸ⁺ or Xʸ
3. Autosomes: vg⁺ or vg
4. Male produces:
5. Sex: Xʸ or Y
6. Autosomes: vg⁺ or vg

1. Sex Chromosomes (X-linked y):

| Xʸ (♂) | Y (♂)

---------|--------------|-------------

Xʸ⁺ (♀) | Xʸ⁺/Xʸ (♀) | Xʸ⁺/Y (♂)

Xʸ (♀) | Xʸ/Xʸ (♀) | Xʸ/Y (♂)

2. Autosomal (vg):

| vg⁺ (♂) | vg (♂)

---------|--------------|-------------

vg⁺ (♀) | vg⁺/vg⁺ | vg⁺/vg

vg (♀) | vg⁺/vg | vg/vg

Genotypic Ratios:

* Xʸ⁺/Xʸ ; vg⁺/vg⁺ → 1/16

* Xʸ⁺/Xʸ ; vg⁺/vg → 2/16

* Xʸ⁺/Xʸ ; vg/vg → 1/16

* Xʸ/Xʸ ; vg⁺/vg⁺ → 1/16

* Xʸ/Xʸ ; vg⁺/vg → 2/16

* Xʸ/Xʸ ; vg/vg → 1/16

* Xʸ⁺/Y ; vg⁺/vg⁺ → 1/16

* Xʸ⁺/Y ; vg⁺/vg → 2/16

* Xʸ⁺/Y ; vg/vg → 1/16

* Xʸ/Y ; vg⁺/vg⁺ → 1/16

* Xʸ/Y ; vg⁺/vg → 2/16

* Xʸ/Y ; vg/vg → 1/16

Phenotypic Ratios:

* Normal body, normal wings → 6/16 (3/8)

* Normal body, vestigial wings → 2/16 (1/8)

* Yellow body, normal wings → 6/16 (3/8)

* Yellow body, vestigial wings → 2/16 (1/8)

F2 summary: The intercross of F1 offspring—females (Xʸ⁺/Xʸ; vg⁺/vg) and males (Xʸ/Y; vg⁺/vg)—produces an F2 generation with the following phenotypic ratios: 3/8 have normal body color and normal wings, 1/8 have normal body color and vestigial wings, 3/8 have yellow body color and normal wings, and 1/8 have yellow body color and vestigial wings. These results reflect independent assortment of an X-linked body color gene and an autosomal wing gene, with recessive phenotypes appearing when homozygous or hemizygous.