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← Theoretical 2

Q94 — Canine Pedigree Analysis of a Monogenic Disease

Theoretical 2 Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Pedigree Analysis & Human Genetic Disorders

Below is a canine pedigree of a common monogenetically inherited disease. Squares and circles represent males and females respectively, and black and white colors indicate the presence or absence of the trait respectively. The numbers indicate the number of dogs in each category and the diagonal lines crossing over squares/circles indicate a deceased dog.

Four-generation pedigree. An unaffected founding pair produces an affected son and several unaffected daughters, three of which are marked with red arrows. The central affected male (generation 2) mates with several of these unaffected, red-arrow-marked females, producing a mix of affected and unaffected offspring in generation 3, some deceased. A dashed box marks a sibling group of four unaffected F1 females on the far left. Canine pedigree of a monogenically inherited trait, spanning four generations. Filled shapes = affected; open shapes = unaffected; diagonal line = deceased; numbers = count of individuals in that category.

Using the information and pedigree, determine whether the following statements are true or false.

A. All the females indicated with red arrows are heterozygous for the trait.
B. The trait could be autosomal recessive.
C. The trait could be X-linked recessive.
D. The genotypes of all four females in F1 (marked with dotted box) must be the same.
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Question reproduced from IBO 2022, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)