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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)
11short 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 is the four common inheritance patterns?Show answer
For each, look for diagnostic features.
What is elimination strategy?Show answer
Work through the pedigree systematically.
What is probability calculations?Show answer
Once you know the inheritance pattern and parental genotypes, use the same Punnett square logic as Mendelian inheritance.
What is 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 reading pedigree symbols incorrectly?Show answer
Squares are male, circles female. Filled means affected.
What is assuming a single example confirms the pattern?Show answer
Look for the pattern across several families or generations.
What is forgetting father to son transmission rules out X-linkage?Show answer
This is the single fastest way to eliminate an X-linked model.
What is confusing the product and sum rules?Show answer
Use product for "and" with independent events; use sum for "or" with mutually exclusive events.
What is forgetting to condition on observed information?Show answer
An unaffected sibling of an affected child does not have a 2/4 chance of being a carrier; given that they are unaffected, they have a 2/3 chance.