IMAT 2021 Q33 [Genetics]

Polydactyly is a condition caused by a gene mutation. Animals affected by polydactyly have extra digits on one or more limbs.

Five inheritance patterns of polydactyly in a species are shown in the diagrams.


Which inheritance pattern can ONLY occur when polydactyly is caused by an autosomal dominant allele and O when it is caused by an autosomal recessive allele?

[Assume normal cell divisions in all individuals.]

A 2

B 1

C 3

D 4

E 5

Hi, most IMAT and BMAT past questions have already been solved in “Ari’s Students” or “IMAT past papers solutions” section of the forum, you can find them easily by typing key terms in the search bar.
If the explanations are still unclear you can of course ask questions on those posts
i hope this helps!

Hi! I found the IMAT past papers solutions section very useful so I am grateful for that. However, for this particular question, I could not find it in there so I was wondering if I can the solution for this

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Could someone explain how you would get to the answer of A? I could narrow it down eliminating some of the easy options - but struggled to get to the answer?

(Couldn’t find this in the past paper questions)

Have to use hit and trial in my opinion. Analyse each pedigree for either cases and the second one for AR won’t be plausible as you can see in the image attached. Sure it’s a time taking question and but won’t take you more than 5/6 mins.

Do you reckon there’s a quicker way to figure it out for exam settings? 2 makes sense now though

Idk mate. I’d suggest leave time consuming q for the end and finish rest first.

A quicker way (I guess - at least it worked for me in this question), is to assume polydactyly WAS caused by recessive alleles. Hence, children of recessive homozygous parents would DEFINITELY have the trait. (2) shows a F2 without the trait being born to 2 recessive homozygous parents → conflicting with the assumption.


Yep, this is what I ended up thinking of as a strat when I looked back on it, thank you! - annoying because it one I should have got -but was conflicted on 2 and 3 and picked the wrong one