Imat 2021 past paper question 26 biology

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4th(option A)?
Let me know so that i can present my explanation

The correct option is E (Diagram-2)

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Hi !

Here it’s easier to go in “reverse” and search for the one that can’t be possible instead of testing each to see if a “dominant” is possible.

We want to find the inheritance pattern that CAN’T be caused by a recessive allele.

We can see in the second “tree” that there are two parents who have the condition that give birth to a child who doesn’t have it.

This would be impossible if the condition was caused by a recessive allele because :
bb + bb → bb (100%)

Whereas if it is a dominant one, as one of the grandparents is negative to the condition(bb), we know for a fact that the affected dad is (Bb). If the mother is (Bb) as well, their offspring could be any of :
→ BB, Bb or bb

Number 2 is then the correct answer.

For the other trees it could be dominant or recessive we just can’t know for SURE.

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Can you again explain in another way , I m still struggling,
I m always getting these types of questions wrong :expressionless:

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Sorry but I am not to understand this question myself.
Try to practice good number of pedigree questions. Because almost every year there is one question like this.


Yeah I’ve been practising pedigrees, but very few questions go right
Anyways thank you !

Maybe @AriHoresh
Can help?