B/B scored exam #58 Genetics

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nznznz

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Assume that K and M are two unlinked genes that affect hearing. The dominant K allele is necessary for hearing, and the dominant M allele causes deafness regardless of the other genes present. Given this, what fraction of the offspring of parents with the genotypes KkMm and Kkmm will most likely be deaf?

A. 1/4

B. 3/8

C. 1/2

D. 5/8


ans:Option D Rationale.This option is correct.This is a Biology question that falls under the content category “Transmission of heritable information from generation to generation and the processes that increase genetic diversity.” The answer to this question is D, because among the offspring of KkMm and Kkmm parents, the ones who lack a dominant K allele (necessary for hearing), or carry a dominant M allele (causes deafness) are deaf. Based on the Punnett square analysis, 10 out of 16 or 5/8 of all offspring are likely to be deaf. This is Scientific Reasoning and Problem Solving question because it requires you to calculate the number of offspring with a particular phenotype from a parental cross.

What's the fastest way to do this problem? How do you do these kinds of problems quickly? Is there a general guideline to follow?

I generally confuse myself with these and try drawing out the punnet squares, but it takes too long. Thanks all

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Fastest way to do this problem, make two different punnet squares for the two different genotypes. So your first cross would be the Kk x Kk which would give you KK, Kk, Kk, kk. The second cross would be Mm x mm which would give you Mm, Mm, mm, and mm. From the second cross you see that half of your offsprings would have to be deaf, as half of them are Mm. Then, you know that from the first cross, any offspring that is homozygous recess (kk) will be deaf. That means that your answer has to be greater than 1/2, because the kkmm offsprings will be deaf as well despite not having the M allele. From there you can answer this question, only one of them is greater than one half. I think their approach is much too time consuming, no one is going to draw out a 16 square punnet square.
 
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Do 2 separate squares as @Wolfpack93 suggests! Do not do the 16 square because it's too time consuming and can be confusing.

Ending up with KK Kk Kk kk and Mm Mm mm mm -> 1/4 will be deaf (kk) and of the remaining 3/4, half of these will also be deaf (if paired with Mm).

1/4 + (3/4 * 1/2) = 5/8.
 
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Do 2 separate squares as @Wolfpack93 suggests! Do not do the 16 square because it's too time consuming and can be confusing.

Ending up with KK Kk Kk kk and Mm Mm mm mm -> 1/4 will be deaf (kk) and of the remaining 3/4, half of these will also be deaf (if paired with Mm).

1/4 + (3/4 * 1/2) = 5/8.


Would doing the math as 1/4 + 1/2 = 3/4 - 2/16 = 10/16 = 5/8 be correct? I know it arrives to the same answer, I just want to confirm that my method is correct. The 2/16 is to account for any "double counting" that would occur when the genotype kkMm appears.

(Also, hello again...another thread to chuckle at my avatar)
 
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Would doing the math as 1/4 + 1/2 = 3/4 - 2/16 = 10/16 = 5/8 be correct? I know it arrives to the same answer, I just want to confirm that my method is correct. The 2/16 is to account for any "double counting" that would occur when the genotype kkMm appears.

(Also, hello again...another thread to chuckle at my avatar)

Is the 1/4 still from the kk (deaf)? What is the addition of 1/2 for?
 
I think that works! The double-counting subtraction is harder for me to keep track of though.

I first thought that half off the offspring will be deaf (Mm). Of the other half get that mm, only 1/4 are deaf (kk). 1/2 + (1/2 * 1/4) = 5/8.
 
I think that works! The double-counting subtraction is harder for me to keep track of though.

I first thought that half off the offspring will be deaf (Mm). Of the other half get that mm, only 1/4 are deaf (kk). 1/2 + (1/2 * 1/4) = 5/8.


Okay, thanks! And the more I look at your way, the more that makes sense.
 
How do you know you can separate it into

Kk/Kk and Mm/mm

I tried KkMm x Kkmm all on the same punnet square, that doesn't work? Is it because in the question it says unlinked?
 
How do you know you can separate it into

Kk/Kk and Mm/mm

I tried KkMm x Kkmm all on the same punnet square, that doesn't work? Is it because in the question it says unlinked?

You can do it in the 16 punnet square but I think that takes more time and space. Doing them separate works because the probabilities are multiplied. I also think it's easier to separate them to think about.
 
How do you know you can separate it into

Kk/Kk and Mm/mm

I tried KkMm x Kkmm all on the same punnet square, that doesn't work? Is it because in the question it says unlinked?


how did you set it up for the 16 punnet square? despite it being a bit more time consuming, that method will get you the correct answer, so long as it is set up properly. i know that if I have a significant amount of time left once I complete B/B, and if I have a question similar to this one, I'm going to go back and double check with the 16 punnet square.
 
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