Short answerModerate1 mark
7(a)
A homozygous dominant tall pea plant bearing red flowers (TTRR) is crossed with a homozygous recessive dwarf pea plant bearing white flowers (ttrr).
Name two X-linked disorders found in humans.
Topic: X-linked disorders
Previous-year question practice database
Answer
Exam answer
- HAEMOPHILIA — the blood fails to clot normally.
- COLOUR BLINDNESS — the inability to distinguish certain colours, usually red and green.
Explanation
Both are carried on the X chromosome as RECESSIVE alleles, which is why both are far commoner in MALES.
THE REASON: a male is XY, so a single defective X is enough — the Y carries no corresponding allele to mask it. A female would need a defective X from BOTH parents, which is rare, so women are usually CARRIERS rather than sufferers.
That asymmetry is the defining feature of sex-linked inheritance and is what examiners test.
Note that ALBINISM, although also a genetic disorder, is AUTOSOMAL recessive and affects both sexes equally — so it would be a wrong answer here.
More from Genetics – Some Basic Fundamentals
Four friends P, Q, R, and S were discussing the examples of genetic disorders. The examples they quoted were as follows:
P. Colour blindness and Malaria
Q. Albinism and Cholera
R. Haemophilia and Colour blindness
S. Haemophilia and Albinism
Who gave the correct examples?2026A family has a history of colour blindness. During genetic testing it was found that the mother is a carrier of colour blindness (XᶜX) and the father has normal vision (XY). What is the probability of their sons being colour blind?2026A scientist wanted to conduct a genetic experiment on mice. He cut the tails of all the mice and made them reproduce. What will be the phenotype of the offsprings?2025Ajay and Vijay are siblings. Ajay can roll his tongue while Vijay cannot. What is the genotype of their parents?2025Define the term Allele.2025Explain the phenotype of the offsprings of the F1 generation obtained from the initial cross.2025