7.1.4 Sex Linkage

• In males, recessive X-linked traits are expressed with only one copy of the allele
• Where are X-linked genes located?

  X chromosome
• Which sex inherits Y-linked traits?

  Males
• Y-linked traits can be expressed in females.

  False
• Sex linkage refers to genes located on the sex chromosomes.
• Females require two copies of a recessive allele on the X chromosome to express a recessive X-linked trait.
• Y-linked genes are located on the Y chromosome.
• Y-linked genes are only present in males.
• What is an example of a Y-linked trait?

  Hairy ears
• What is sex linkage in humans?

  Genes on sex chromosomes
• Match the sex with its chromosome composition and trait expression for recessive X-linked traits:

  Male ↔️ XY; single X means one recessive allele expresses trait

  Female ↔️ XX; two X chromosomes require two recessive alleles
• Y-linked genes are present in females.

  False
• What is the chromosome composition of males for X-linked genes?

  XY
• Recessive X-linked traits are more common in males
• What is the chromosome composition of a male in humans?

  XY
• What is an example of an X-linked recessive trait?

  Color blindness
• Which parent can pass X-linked traits to both sons and daughters?

  Mother
• Match the trait type with its inheritance pattern:

  X-linked ↔️ Mothers pass to sons and daughters ||| Affected fathers pass to daughters only

  Y-linked ↔️ Only passed from father to son
• Steps to distinguish between X-linked and Y-linked traits in pedigree analysis:

  1️⃣ Examine inheritance patterns across generations

  2️⃣ Identify if the trait is more common in males

  3️⃣ Determine if affected mothers pass to both sons and daughters

  4️⃣ Confirm if affected fathers pass only to daughters
• Females require two copies of a recessive X-linked allele to express the trait.


  True
• Males with a single X chromosome express recessive X-linked traits with one allele
• Y-linked traits are only passed from father to son
• How many X chromosomes do females need to express a recessive X-linked trait?

  Two
• Recessive X-linked traits are more common in males.


  True
• X-linked genes are located on the X chromosome.


  True
• Y-linked traits are passed down from father to son.


  True
• Females with two X chromosomes require two copies of a recessive allele to express an X-linked recessive trait.


  True
• X-linked traits are more common in males because they only need one copy of the recessive allele.