Sex Determination and Linkage Quiz

Sex Determination and Sex Linkage

• Sex determination is primarily controlled by genetic and hormonal factors.
• Four types of chromosomal sex-determining mechanisms exist: XY, ZW, XO, and compound mechanisms.
• In humans and most mammals, sex is determined by the presence of two different sex chromosomes (X and Y). These are heteromorphic, meaning they differ in size and shape.

XY Sex Determination Method

• Males have 22 pairs of autosomes and one X and one Y chromosome. They produce two types of sperm: X-bearing and Y-bearing.
• Females have 22 pairs of autosomes and two X chromosomes, producing only X-bearing eggs.
• This system results in a 50/50 chance of the offspring being male or female.

Heterogametic Females (ZZ-ZW)

• This method is found in many birds, butterflies, moths, and some fish.
• Females are heterogametic (ZW) while males are homogametic (ZZ).
• The mode is similar to the XY mechanism.

Sex Linkage

• Sex linkage describes inheritance patterns of genes located on the sex chromosomes (X and Y).
• Genes on sex chromosomes are called sex-linked.
• Their expression and inheritance patterns differ between males and females.
• Holandric genes are completely Y-linked, passing only from father to son.

X-Linked Disorders

• Many human traits are X-linked, including color blindness, hemophilia, and Duchenne muscular dystrophy.
• X-linked disorders are more prevalent in males since they have only one X chromosome.
• Females can be carriers of X-linked recessive genes, but the trait more easily shows up in male offspring.

X-Linked Recessive Disorders

• More males than females are affected. Affected males cannot pass the disorder to their sons, but all daughters will be carriers.
• Carrier females have a 50% chance of passing the mutation to their offspring.
• Examples include hemophilia (impaired blood clotting).

X-Linked Dominant Disorders

• Both males and females can be affected.
• Affected males pass the disorder to all daughters but not sons.
• Affected females have a 50% chance of passing the disorder to their offspring
• An example is Rett Syndrome

Fragile X Syndrome

• A genetic condition causing intellectual disability, behavioral challenges, and distinctive physical features.
• Symptoms include learning disabilities, developmental delays, social and behavioral problems.

Additional Information

• Researchers like Henking, McClung, and Wilson investigated the relationship between chromosomes and sex determination.
• The SRY (Sex-determining Region Y) gene is located on the short arm of the Y chromosome and is crucial for male development.