Question

1. What type of gene is found on a sex chromosome?
• A. growth factors
• B. oncogene
• C. sex-linked
• D. tumor-suppressor
Comprehension Questions
2. What makes sex chromosomes different from other chromosomes?
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3. What are the two types of sex chromosomes in humans?
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4. What do we call a gene that is located on a sex chromosome?
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5. Why might sex-linked traits affect males and females differently?
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Short Response
6. Think about how genes determine traits. Describe one example of a trait that could be affected by a sex-linked gene and explain why. (Write 2–3 sentences.)
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Answer 1

1. C. sex-linked

2. Sex chromosomes are different because they determine an individual’s sex (male or female) and are not identical in the two sexes. Humans have one pair of sex chromosomes that differ in size and gene content (especially X vs. Y), while the other chromosome pairs (autosomes) are the same in males and females.

3. The two types of sex chromosomes in humans are X and Y.

4. A gene located on a sex chromosome is called a sex-linked gene (often specifically X-linked or Y-linked).

5. Sex-linked traits can affect males and females differently because males have only one X chromosome (are hemizygous for X-linked genes), so a single recessive allele on the X will be expressed in males, whereas females have two X chromosomes and a recessive allele can be masked by a dominant allele on the other X. Also, the Y chromosome carries few genes, so Y-linked traits affect only males.

6. Example: Red-green colorblindness is an X-linked recessive trait. A male who inherits the colorblind allele on his single X will be colorblind, while a female would need the allele on both of her X chromosomes to be colorblind, so females are less likely to show the trait and often are carriers.