OpenRevise

Flashcards · Biology · Inheritance

Sex-Linked Genetic Disorders (Higher tier)

16 cards

  1. What is a sex-linked gene?

    A gene on a sex chromosome, usually the X chromosome.

  2. Why are males more likely to have a sex-linked recessive disorder?

    They have only one X chromosome, so a single recessive allele shows.

  3. Can a male be a carrier of a sex-linked recessive allele?

    No. If he has the allele, he has the disorder.

  4. What is the genotype of a carrier female for haemophilia?

    \(X^H X^h\).

  5. What is the genotype of a male with haemophilia?

    \(X^h Y\).

  6. What is the genotype of an affected female?

    \(X^h X^h\).

  7. Name two sex-linked recessive disorders.

    Haemophilia and red-green colour blindness (also Duchenne muscular dystrophy).

  8. What happens in haemophilia?

    The blood does not clot properly.

  9. A carrier mother and a normal father: what is the chance of an affected son?

    1 in 2 (50%) for each son.

  10. A carrier mother and a normal father: what is the chance of an affected child?

    1 in 4 (25%).

  11. Can a father with haemophilia pass it to his son?

    No. He passes his Y chromosome to his sons.

  12. What will the daughters of an affected father and a normal mother be?

    All carriers.

  13. Who was a famous carrier of haemophilia?

    Queen Victoria.

  14. Is colour blindness more common in men or women?

    Men.

  15. Why does a female need two recessive alleles to be affected?

    A dominant allele on her other X chromosome hides the recessive one.

  16. What is the common mistake about sex-linked inheritance?

    Writing the alleles on the Y chromosome. The Y has no matching allele for the gene.