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QLDBiologyQuick questions
Unit 4: Heredity and continuity of life
Quick questions on Pedigree analysis and inheritance probability (QCE Biology Unit 4)
6short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What are identifying carriers?Show answer
In an autosomal recessive pedigree, an unaffected child of two carriers has a 2/3 chance of being a carrier (given they are unaffected). This is a common stumbling block: do not just halve the 1/2 carrier offspring probability without conditioning on the observation.
What is y-linked?Show answer
Rare. Passes father to son only. Affects only males.
What is worked example?Show answer
Two carriers Cc x Cc. What is the probability the next two children are both affected (cc) girls?
What is q1?Show answer
Identify three features of a pedigree that suggest autosomal recessive inheritance. [3 marks]
What is q2?Show answer
In a pedigree, two unaffected parents have three children, one of whom is affected. Calculate the probability that the next child is also affected and explain whether this depends on the previous outcomes. [3 marks]
What is q3?Show answer
Refer to an X-linked recessive pedigree. (a) Identify one feature confirming X-linked rather than autosomal pattern. (b) Calculate offspring probability for a carrier mother and unaffected father producing an affected son.
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