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Genetic Variation & Change · Part 3 of 4
6 exam-style questions with model answers, plus 8 quick multi-choice questions — every question on this part of the standard, grouped by the 2 pages of notes they come from.
Write a full answer before you reveal the model one. That comparison is where the learning happens.
Define linked genes, and state why linked genes do not follow independent assortment.
Explain how crossing over produces recombinant offspring when two genes are linked, and explain why recombinants are less common than parental types.
A geneticist studies three linked genes, A, B and C, on the same chromosome. Test crosses give recombination frequencies of 8% between A and B, 12% between B and C, and 20% between A and C. Discuss what these data reveal, and evaluate the limitations of using recombination frequency in this way.
Explain what is meant by a sex-linked gene, and write the genotype of a female who is a carrier for an X-linked recessive condition.
Explain why X-linked recessive conditions such as red–green colour blindness are far more common in males than in females.
A researcher examines a family tree for a condition that appears in several males across three generations but in no females, and always skips the fathers of affected individuals. Discuss what pattern of inheritance this indicates, how alternative explanations can be ruled out, and what advice could be given to a carrier woman.