Which of the following statements about sex linked traits is not correct?

Analyze the question: We need the statement that is NOT correct about sex-linked traits (mostly X-linked traits, e.g., colour blindness and haemophilia).

Concept:

• Females are XX; males are XY.
• A son receives his Y chromosome from his father and his X chromosome from his mother.
• X-linked genes are carried on the X chromosome. Males have only one X (hemizygous), so a single recessive allele shows up in them.
• Females can be heterozygous (X^H X^h), so they can be carriers without showing the trait.

Check each option:

• A. Males inherit sex-linked traits from their fathers. This is false. A father passes his Y to his sons, and the Y carries no allele for X-linked traits like colour blindness. Sons get the X-linked trait from their mothers. (Fathers pass their X to their daughters, not their sons.)
• B. Sex-linked traits are more common in males. This is true. One recessive allele is enough for a male to show the trait.
• C. Females can be carriers because they can be heterozygous. This is true.
• D. Males are never carriers since they only receive one sex chromosome. This is the textbook idea. Males have only one X, so if they have the allele they show the trait and are not "carriers" in the heterozygous sense. Strictly, they receive two sex chromosomes (X and Y), so the reason is worded loosely. But the main idea, that males cannot be carriers of X-linked recessive traits, is accepted.

Answer: Option A is the incorrect statement.

Worked example: Colour-blind father (X^c Y) × normal non-carrier mother (X^C X^C):

• Sons: X^C Y, all normal. They got X from the mother and Y from the father.
• Daughters: X^C X^c, all carriers.

The father's colour blindness was not passed to his sons.

Exam tip: Remember "Sons get their X from Mum." Whenever an option says a son inherits an X-linked trait from his father, mark it wrong.