Principles of Inheritance and Variation — Practice

Question 1

A Tt x tt cross produces 200 offspring. How many are tall?

Accepted Answer

Tt x tt gives 1 Tt (tall) : 1 tt (dwarf), so about 100 are tall.

Question 2

If the father is I^A I^B and the mother is I^A i, what blood groups can the children have?

Accepted Answer

Offspring genotypes: I^A I^A (A), I^A i (A), I^A I^B (AB), I^B i (B). Possible blood groups: A, B, and AB.

Question 3

Why is colour blindness more common in males than females?

Accepted Answer

Colour blindness is X-linked recessive. Males have only one X, so a single mutated allele makes them colour blind. Females need two mutated alleles (one on each X), which is far rarer.

Question 4

Differentiate between Turner and Klinefelter syndromes.

Accepted Answer

Turner syndrome (45, XO) is a female who is short, sterile, with a webbed neck. Klinefelter syndrome (47, XXY) is a male who is tall, sterile, with reduced testosterone.

Question 5

In a YyRr x YyRr cross, what is the probability of a YYRR offspring?

Accepted Answer

P(YY) = 1/4 and P(RR) = 1/4. By independent assortment, P(YYRR) = 1/4 x 1/4 = 1/16.

Practice — Principles of Inheritance and Variation

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