Home / IB DP Biology- D3.2 Inheritance- IB Style Questions For HL Paper 1A

IB DP Biology- D3.2 Inheritance- IB Style Questions For HL Paper 1A -New Syllabus

IBDP Biology HL Paper 1 -All Chapters

Question

The pedigree chart shows the incidence of colour blindness in three generations of a family. Colour blindness is caused by a sex-linked recessive allele.

What could the genotype of individual Z be?

(A) XBXB only
(B) XBXb only
(C) XBXB or XBXb
(D) XbXb or XBXb
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathbf{C}} \)

Since the family has an affected son, the mother must be a carrier (XBXb), while the father is unaffected (XBY). Individual Z is an unaffected female, so she could be either XBXB or XBXb (a carrier).

Question

A Mirabilis jalapa (four o’clock) plant bearing red flowers was crossed with one that had white flowers. The offspring in the F₁ generation all showed pink flowers. What phenotypic ratio would most likely be observed in the F₂ generation?

A. 100% pink
B. 50% red and 50% white
C. 25% white, 50% pink and 25% red
D. 75% red and 25% white

▶️ Answer/Explanation
This cross demonstrates incomplete dominance. When red-flowered and white-flowered plants are crossed, the F₁ generation shows pink flowers (a blend of the two). In the F₂ generation, the segregation of alleles produces a phenotypic ratio of 1 red : 2 pink : 1 white, or equivalently, 25% red, 50% pink, and 25% white.
✅ Answer: (C) 25% white, 50% pink and 25% red

Question

Scientists incubated larvae of the moth Utetheisa ornatrix at 15 °C or 22 °C. The adults had different wing colour patterns due to phenotypic plasticity. Which statement explains the observed differences?

(A) Colder temperatures induce mutations in genes for wing colour.
(B) The expression of genes for wing colour is affected by temperature.
(C) A mutation makes moths less visible to predators in cold climates.
(D) Wing colour is the result of polygenic inheritance.
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathbf{B}} \)

Phenotypic plasticity is the ability of the same genotype to produce different phenotypes in response to environmental conditions. In this case, temperature affects the expression of genes involved in wing colour, resulting in different colour patterns without changing the DNA sequence.

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