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FL1 B/B #58

Posted: Thu Sep 05, 2019 2:29 pm
by Amber9

Can we find the portion of offspring who lack the dominant K allele and then find the portion of offspring who carry the dominant M allele and multiply the fractions? KkMm and Kkmm parents would give 1/4 recessive kk offspring and 1/2 heterozygote Mm offsprings, it does not give me 5/8.

Re: FL1 B/B #58

Posted: Mon Sep 09, 2019 3:23 am
by NS_Tutor_Mathias
Multiplying fractions makes them smaller. You want to add up all the conditions, and the most sensible way to do that is with a Punnet square. Any other arithmetic approach uses non-MCAT math and is not advisable. You cannot apply a probability approach here, because that does not account for the overlap of conditions (like a kkMm).

If you are pressed for time, estimation is a valid strategy too:
At least one half MUST be deaf, because one dominant M parent is present, meaning half of all gametes will contain dominant M. You know from experience with Punnet squares or just imagining combinations that at least one kkmm must be possible. So the absolute minimum number of deaf offspring is greater than 1/2 - making D the only option.