Which of the following statements is true regarding sex-linked traits?

Step 1: Analyze the question We need to pick the one true statement about sex-linked traits.

Step 2: The concept Sex-linked traits are controlled by genes located on the sex chromosomes (X and Y). Most are X-linked, such as colour blindness, haemophilia and Duchenne muscular dystrophy. Females are XX and males are XY.

Step 3: Evaluate each option

• A. Sex-linked traits are located on the sex chromosomes. True. This is the definition of a sex-linked trait.
• B. Inherited only from the mother. False. X-linked genes can come from either parent. A daughter receives one X from her father and one from her mother. A son gets his X from his mother, but Y-linked traits pass from father to son.
• C. More commonly observed in females. False. X-linked recessive traits are more common in males because males have only one X chromosome (hemizygous). A single recessive allele is enough to show the trait. Females need two copies.
• D. Not influenced by hormonal factors. This is too absolute and not a defining statement. Hormones can influence how some traits are expressed (sex-influenced traits like pattern baldness), so this option is not a reliable true statement.

Step 4: Answer Option A is correct.

Tip: Remember "sex-linked = on the sex chromosomes". For X-linked recessive traits, males are affected more often because they have only one X. In the exam, be careful with words like "only" and "not", since they often make an option false.