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2.6 Sex-Linked Inheritance & Criss-Cross Patterns โ Test 3
Q1. Which of the following is a classic sex-linked (X-linked recessive) disorder in humans?โ Colour blindness
Q2. A colour-blind father and a homozygous-normal mother have sons. The probability that a son is colour blind is:โ 0%
Q3. A man's paternal grandfather was haemophilic. The probability that this man (the grandson) is haemophilic via that line is:โ 0
Q4. Which statement about X-linked recessive disorders is NOT correct?โ An affected male passes the trait to all of his sons
Q5. Criss-cross inheritance (trait passing from an affected male to his grandsons through his daughters) is characteristic of:โ Sex-linked (X-linked recessive) traits
Q6. A possible cause of unequal results in reciprocal crosses is:โ X-linked inheritance
Q7. A woman known to carry a genetic disorder marries a normal man. All her daughters survive but all her sons die. The disorder is most likely:โ X-linked recessive (lethal in hemizygous males)
Q8. In Drosophila, a red-eyed female (homozygous) crossed with a white-eyed male gives all red-eyed F1; the reciprocal cross (white female ร red male) gives red-eyed daughters and white-eyed sons. This 'criss-cross' result indicates the gene is:โ X-linked
Q9. Male-pattern baldness, which behaves as dominant in males but recessive in females, is an example of a:โ Sex-influenced (sex-conditioned) trait
Q10. A trait expressed in only one sex (e.g. milk yield in cattle, expressed only in females) is a:โ Sex-limited trait
Q11. A gene located on the non-recombining part of the Y chromosome shows ___ inheritance:โ Holandric (Y-linked, father to son)
Q12. Males are described as 'hemizygous' for X-linked genes because they:โ Have only one copy of each X-linked gene
Q13. In sheep, horns are produced by an autosomal allele H that is dominant in males but recessive in females. A horned female (HH) is crossed with a hornless male (hh). Among the F1:โ All males are horned; all females are hornless
Q14. In a pedigree, an absolute exclusion of X-linked recessive inheritance is provided by:โ Father-to-son (male-to-male) transmission
Q15. A carrier mother for red-green colour blindness marries a man with normal vision. The proportion of their SONS expected to be colour blind is:โ 1/2 (half of sons)
Q16. Polydactyly is a dominant trait, yet some individuals carrying the dominant allele show no extra digits. This is due to:โ Incomplete penetrance
Q17. A dominant allele causes polydactyly. Of 42 individuals carrying the allele, only 38 are polydactylous. The penetrance is about:โ 90%
Q18. Genes in the pseudoautosomal regions at the tips of the X and Y chromosomes:โ Are present on both X and Y and recombine during male meiosis
Q19. A trait determined by a recessive X-linked allele will show which inheritance feature?โ Higher incidence in males than females
Q20. Match each term with its description and select the correct option.โ A-ii, B-iii, C-i, D-iv