Sex Linked Disorders | Biology for JAMB PDF Download

Introduction

Sex-linked characters, also known as sex-linked traits, refer to genetic traits that are controlled by genes located on the sex chromosomes, specifically the X chromosome in humans. These traits are typically expressed more frequently in one sex than the other due to differences in the inheritance patterns of the X and Y chromosomes. Common examples of sex-linked characters include baldness, hemophilia, and color blindness. This note aims to provide a comprehensive understanding of these sex-linked characters as per the JAMB Biology syllabus.

Baldness

• Baldness is a sex-linked character commonly associated with males.
• It is caused by a dominant allele (B) on the X chromosome.
• Females require two copies of the dominant allele to express the trait, while males require only one.
• Baldness can be inherited from either the mother or the father.
• The recessive allele (b) represents the absence of baldness and is more prevalent in the population.

Hemophilia

• Hemophilia is a sex-linked recessive disorder.
• It is characterized by impaired blood clotting due to the absence or malfunctioning of certain clotting factors.
• The gene responsible for hemophilia is located on the X chromosome.
• Females can be carriers of the hemophilia gene, but they are typically unaffected due to the presence of a normal allele on their other X chromosome.
• Males who inherit the hemophilia gene are more likely to express the disorder since they only possess one X chromosome.

Color Blindness

• Color blindness is a sex-linked recessive trait that affects the perception of colors.
• It is caused by mutations in genes located on the X chromosome.
• The most common form of color blindness is red-green color blindness.
• Females can be carriers of the color blindness gene, but they are typically unaffected due to the presence of a normal allele on their other X chromosome.
• Males who inherit the color blindness gene are more likely to express the trait since they only possess one X chromosome.

Other Sex-Linked Characters

• In addition to baldness, hemophilia, and color blindness, there are other sex-linked characters as well.
• Examples include Duchenne muscular dystrophy, which affects muscle strength, and X-linked ichthyosis, a skin disorder.
• These traits follow similar patterns of inheritance, with males being more susceptible to their expression.

Conclusion

Sex-linked characters, such as baldness, hemophilia, and color blindness, are genetic traits controlled by genes on the X chromosome. Due to the inheritance patterns of the sex chromosomes, these traits are more commonly expressed in one sex compared to the other. Understanding the inheritance and characteristics of these sex-linked characters is crucial for comprehending the impact of genetics on human health and development