Sex Linked Inheritance

Jamie Z 2024-11-04

Learning Goals

• Describe the difference between X-linked dominant, X-linked recessive
• Represent sex-linked alleles using standard notation.
• Identify examples of traits which are X-linked dominant and X-linked recessive
• Explain how these three types of inheritance result in different prevalances of a trait between genders ( X-linked dominant more common in males, X-linked recessive more common in females).
• Determine the potential ratios of offspring genotypes and phenotypes in monohybrid crosses involving sex linked gene pairs

Sex Determination

• The sex of an individual is usually determined by the sex chromosomes provided by each parent
• In humans, males are heterogametic because each somatic cell has one X and one Y chromosome
• Sex determination is based on the presence or absence of the Y chromosome

• If a baby inherits a X chromosome from the father and mother the baby will have two X chromosomes (female)
• If the father’s sperm carries the Y chromosome the baby will be male

Sex linked Genes

• Genes are located on the sex chromosomes of an individual
• Genes on the X chromosome are said to be X-Linked
• Recessive X-linked genetic disorders are much more common in males than females due to the X linked inheritance pattern
• If a male has a “bad” allele from his mother, he has no chance of getting a “good” allele
• Females, on the other hand, will often receive a normal allele from their fathers, preventing the disease allele from being expressed

Sex linked traits affect males and females differently

	Males	Females
Normal	\(X^AY\)	\(X^AX^A\)
Affected	\(X^AY\)	\(X^aX^a\)
Carrier		\(X^AX^a\)

Examples

• EXAMPLE: HAEMOPHILIA: Impairment the body's ability to control coagulation – blood does not clot properly.
• EXAMPLE: COLOUR BLINDNESS: Inability to perceive differences between some or all colours that other people can distinguish