Sex-Linked Inheritance
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Learning Objective
In this lesson we will learn how traits controlled by genes located on sex chromosomes follow different patterns of inheritance in males and females.
Learning Outcomes
- Explain what a sex-linked trait is and differentiate between X-linked and Y-linked traits.
- Write genotypes for sex-linked traits and describe hemizygosity in males.
- Determine genotypes and phenotypes for X-linked and Y-linked traits in males and females.
- Compare sex-linked inheritance in males and females.
(Image: nechaevkon, Adobe Stock)
Lesson Summary
- Sex-linked traits are controlled by genes located on sex chromosomes.
- X-linked traits are controlled by genes on the X chromosome.
- Y-linked traits are controlled by genes on the Y chromosome.
- Sex-linked inheritance follows different patterns in males and females as they have different numbers of alleles for sex-linked traits.
- Most cases of sex-linked inheritance are X-linked.
- For X-linked genes, males have one allele (from their mother) and females have two alleles.
- Males are hemizygous – they cannot be homozygous or heterozygous. They express the phenotype of whichever allele they possess.
- Females express X-linked traits in the same way as autosomal traits.
- For Y-linked genes, males have one allele (from their father) and females have no alleles.
- Males express Y-linked traits in the same way as X-linked traits.
- Females do not possess Y-linked traits.
- Sex-linked alleles are written as superscript letters in combination with an X or Y.
Do you see a number in this picture? Colour blindness is linked to a gene on the X chromosome. It causes individuals to have difficulty differentiating between certain colours, such as red and green.
(Image: Desconocido, Wikimedia Commons)
(Header image: Atypeek Design, Adobe Stock)