Genetic Pedigree Multiple Choice Quiz – 1

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This is the first little quiz to test your knowledge on genetic pedigrees and inheritance patterns. There are 5 pages with dummy pedigrees followed by some real-world examples from published works. Links to the other quizzes are at the bottom of the page.

Q1. Which of these inheritance patterns would be the most likely explanation of the above pedigree? Click on the correct answer(s), the text turns green if you are correct. You can also click on other answers for explanations.
Autosomal Recessive.
X-linked Recessive.
Although the left hand-side of the pedigree could be explained by X-linked recessive if the unaffected grandmother was a carrier, on the right hand side you have an unaffected male being born from an affected mother. For this inheritance to be explained by X-linked recessive, it would have to have incomplete penetrance.
Autosomal Dominant.
No, the condition is skipping a generation. For dominant conditions, an affected person could not be born from unaffected parents.
Mitochondrial conditions pass down the maternal lines. the offspring of the female on the right hand-side would be affected.
Based on the answer to Q1, what is the probability that the new-born male marked with ?1 will be affected by the condition?
As there are two affected individuals that have been born from this couple, you can infer that both parents are carriers of the affected allele. Therefore, there is definitely >0% chance that a further child will be affected. How much more than 0? Have a think and try again.
If the inheritance is autosomal recessive and the two parents are unaffected then that means that each must be a carrier. To present with the disease requires the affected allele to be obtained from BOTH parents. There is a 50% chance of the affected allele coming from the father and 50% from the mother 50% x 50% = 25%
I don’t know how you have come up with this number! Remember that the probability of one child being affected is independent of what has been the outcome from previous children.
This isn’t correct – you already knew that really, these parents have already had unaffected children therefore there can’t be a 100% chance! Have a think and try again!
If the child marked ?2 was NOT affected by the condition. What would you tell the father of that child?
We do not know if you are a carrier of the condition or not; however, your child is a carrier.
We can actually infer whether the father is a carrier or not… try again
You are a carrier of the condition and so is your child
anytime you have an offspring from an affected individual, then they must be a carrier. They will have received one allele from the affected individual. Therefore, both are carriers
You are not a carrier of the condition but your child is.
As the father’s own mother was affected, then he must have received one allele from her and, therefore, is a carrier.
We do not know if you or your child is a carrier of the condition
We actually can infer these points… have a think and try again!
You are a carrier of the condition but your child is not.
This one can’t be right – the child’s mother is affected, therefore, at minimum the child must be a carrier.
You are both affected but we can’t detect the disease yet
While this is possible, from the information available we can not make that inference.

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