Wow. Been struggling with these problems for so long. No one ever explained the "and" = multiply. Mind. Blown. Looking foward to watching more of your videos!
I try to create questions similar to ones my students struggle with, because I know that means others are having a hard time with them too. I'm glad it helped!
For Q3, I did HhAa x HhAa with two smaller punnett squares (Hh x Hh and Aa x Aa) then multiplied the results to find the probability of hh and any genotype including "A" and got the same answer: 1/4 x 3/4 = 3/16. Was this a coincidence or will that work every time as well? thank you so much for your videos! They are so helpful!!
It works in fully heterozygous dihybrid crosses, but unfortunately that math will not always work out in other situations or questions! I think the safest way is to do out the dihybrid square like in the video - there are other ways to do the probabilities with monohybrid punnett squares, but those questions require additional math and using different types of probability calculations for different set ups, which is (in my opinion) a more risky way to do these problems, and takes about the same amount of time as just setting up the axes :).
Yes it is! For me personally, I try to avoid additional calculations on the MCAT since it is so easy to make a small calculation error. However, you're math absolutely would work for this problem.
Hi @bioeducate - I checked through the video and I'm assuming you are referring to the math in the first question. In this scenario, we are multiplying 1/2 x 1/2 x 1/2. When we multiply the denominators, we are multiplying 2 x 2 x 2, which is 2^3 (exponential math) NOT 2 x 3. So our math here will give us a value of 1/8! Hope this helps.
Thank you so much for the video! Question 3 I did two individual monohybrid punnet squares for the traits separately and I was able to get 3/16. But in the video, you said you would not recommend that, why is that?
Glad you liked it! While you can do two monohybrid squares for most dihybrid cross questions, I find it is much easier to make mistakes that way and you have to do calculations, whereas the dihybrid cross square takes slightly longer in the set up, but requires no math and often is less prone to mistakes!
For that question, we didn't need to specify which beetle was which sex - we knew both the male and female parents needed to be heterozygous to get the progeny in the question stem, and since the parents were both the dominant phenotype, we can determine the probability for both sexes was 2/3! In this case, we can infer that this gene is autosomal, not sex-linked, since the question stem didn't specify sex-specific inheritance patterns in the original crosses. Hope this helps!
so AAMC FL1 has one that talks about unlinked genes and a cross with one heterozygote for both traits and the other being heterozygote(for one trait) and the other trait being homozygous recessive? How would you go about that in a timely manner? Recommend doing the whole punnet square and do something similar to what you did In the last example?. So the traits were for hearing and not hearing----- Needed to have one K(hearing) to hear but if you have any genotype with M you would be deaf. The Genotypes were KkMm X Kkmm
I did write the dihybrid cross question with that exact question in mind! Yes, I would do exactly the same process as in the video - figure out the four potential gamete combinations for each parent (there would be will be redundant combinations for the non-heterozygote parent: two gametes would be Km and two would be km) and write them along the axes of the 16-cell punnett square. Then use which genotype(s) you are looking for to eliminate rows and columns until you are left with your answer. Hope this helps!
I understand the multiplication rule for the three sons. Can you please help me understand what would change in the question that would lead us to add instead of multiply. Overall when do we add probabilities ? Thank you for the videos btw
In general, we add probabilities when it is an OR question. So if you wanted to calculate the chances of having a male OR female offspring, you would add the probability of having a male (50%) + the probability of having a female (50%), which would give you 100%. We don't often see this on MCAT genetics questions - they often ask "AND" questions where we need to multiply!
