Multiple Choice
Which allele combination represents a female who is heterozygous for a sex-linked trait?
2
views
2. Mendel's Laws of Inheritance
Sex-Linked Genes
Struggling with Genetics?
Join thousands of students who trust us to help them ace their exams!Watch the first videoMultiple Choice
In a cross between a homozygous normal female (XX) and a male affected by an X-linked recessive disorder (X^aY), why are there no affected females in the F1 generation?
A
All F1 females inherit one normal allele from their mother and one affected allele from their father, making them carriers but not affected.
B
F1 females inherit only Y chromosomes from their father, so they cannot be affected.
C
All F1 females inherit two affected alleles, so they are all affected.
D
The disorder is dominant, so only males are affected in the F1 generation.
Verified step by step guidance1
Identify the genotypes of the parents: the female is homozygous normal (X\^N X\^N) and the male is affected by an X-linked recessive disorder (X\^a Y).
Determine the possible gametes each parent can produce: the female can only produce X\^N eggs, and the male can produce X\^a sperm or Y sperm.
Combine the gametes to find the genotypes of the F1 offspring: females receive one X chromosome from each parent, so all F1 females will be X\^N X\^a, and males receive the X chromosome from the mother and Y from the father, so all F1 males will be X\^N Y.
Understand the expression of the X-linked recessive disorder: females need two copies of the affected allele (X\^a X\^a) to be affected, while males only need one copy (X\^a Y) because they have only one X chromosome.
Conclude that since all F1 females have one normal allele (X\^N) and one affected allele (X\^a), they are carriers but not affected, which explains why no females in the F1 generation show the disorder.
Related Videos
Related Practice
Sex-Linked Genes practice set
Problem sets built by lead tutorsExpert video explanations