Introduction

As we saw previously, most pairs of homologous chromosomes are exactly alike in terms of length, shape, and the set of genes they carry. However, in humans and many other organisms, this is not true of the chromosomes that determine the sex of the organism. In humans, males possess one X chromosome and one Y chromosome, whereas females have two copies of the X chromosome.

The following video explains what Sex-Linked Traits are with examples.

Summary

In this section, we have learned:

• Humans possess 23 pairs of chromosomes; one of these pairs, the sex chromosomes (X and Y) are responsible for determining the sex of the individual.
• Females possess 2 copies of the X chromosome; males possess 1 copy of the X and 1 copy of the Y chromosome.
• Females produce gametes (eggs) that contain 1 copy of the X chromosome; Males produce gametes (sperm) that contain either an X or a Y chromosome.
• Genes located on the X chromosome are considered to be sex-linked and have different inheritance patterns depending on the sex of the offspring.
• Since males possess only 1 copy of the X chromosome, only 1 defective copy of a sex-linked gene is required to affect the individual.
• Since females possess 2 copies of the X chromosome, they would need 2 defective copies (homozygous) of a ‘recessive’ gene to affect the individual.
• In general, males are more likely than females to suffer from X-linked disorders.
• Examples of X-linked disorders include hemophilia, and Duchenne muscular dystrophy.

Sources:

“Sex Linked Genes.” By Flippin’ Science Videos. Retrieved from: https://www.youtube.com/watch?v=y9y-p-5ofAA