2021HSCShort answer

Q24 (b)

4 marks

Question

An incidence of an autosomal dominant trait is shown in the pedigree. KEY Unaffected female Unaffected male Male with trait The diagram shows the early stages of embryonic development from a fertilised egg. The developing ball of cells has split and monozygotic (identical) twins have formed. Mutations can occur at different times during embryonic development, for example Mutation A would result in both twins having the mutation in all their cells.
Explain the effects of Mutation B and Mutation C on each twin and on any offspring that they may have.

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Solution

Sample answer: Mutation B occurred after twin formation, therefore affecting only Twin 1. Because it occurred prior to formation of the germ cells it will be evident in both the germ cells and the somatic cells of Twin 1 and through the germ cells may be passed to the offspring. Because Mutation C occurs in the cells leading to somatic cells in Twin 2 only, it will be evident in the somatic cells of Twin 2 but not in the germline cells and can’t be passed on to offspring.

Marks:
4 - Explains the effects of the mutations on the twins and their offspring
3 - explain some of the effects of the mutations on the twins and/or their offspring
2 - Demonstrates some understanding of the effect(s) of the mutation(s)
1 - Provides some relevant information

Supplied marking guidance · human reviewed

Compare this with your working, not only your final sentence.

Syllabus alignment

Module 6 · Genetic Change

MutationDistinguish somatic and germ-line mutations and their effects on organisms.

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