How to Solve MCAT Genetics Probability Problems | MCAT

[@medcatmcat]

Just an update since I've been in medical school: this type of problem is representative of the types of problems you might see in a genetics question in your preclinical years! Of course, you won't be dealing with flies, but rather genetic conditions of all different inheritance types.

[@futuredoc7303]

Thank you so much, this was very helpful! Please make more high-yield MCAT videos where you walk us through the process of solving problems, these are golden resources. Wish more people knew about this channel!

[@medcatmcat]

Thank you!

[@sarahalshimary9849]

i usually dont comment on youtube videos but im taking my mcat the day after tomorrow and you rly made this click for me. ive been binging your videos since i wanted to do some light content review and ive learned so much. thank you and i hope youre doing well in med school

[@medcatmcat]

Glad I could help! Thank you so much; these comments make my day. I am doing well!

[@ArianaMoore-ov1tb]

10/10 thank you so much! This video helped me so much on AAMC 4 exam!!!

[@medcatmcat]

I'm glad I could help!

[@akankshabhatt3357]

Thankyou so much! This video breakdown was super helpful, please do make more videos on complex topics!

[@medcatmcat]

Thank you!

[@airquis]

Thank you i have just one question, why aren't the yellow dominant alleles ignored in the probability. I'm assuming its because the problem stated that 2 yellow flies are going to be mated?

[@swiper1679]

This video just cleared up all my confusion 🙌🏽 Thank you!

[@medcatmcat]

Thank you:)

[@mzzsweetluv19]

Hi! I’m confused about why we’re only focusing on yellow flies when it’s asking for the probability of yellow and white flies. Thanks for your help!

[@vchoe4616]

Because On the question, it says “if two yellow F1 flies are crossed…”.

[@medcatmcat]

Hi! Thanks for the question. I concur with V Choe: we are crossing two yellow flies.

[@JT-tx2ns]

thanks for asking this because it was confusing to me too but now it's obvious. the mcat has such tricky wording, it can easily steal points if you're not careful!

[@dianeabaidoo1438]

so if i am understanding correctly both (2/3) fractions came from the F1 punnet for each Ww probability to calc F2 probability?

[@anjelicashrestha3645]

hi thank u for a wonderful video! i was just a bit confused about the calculation towards the end - why do multiple (2/3) x (2/3) at the end? thank u!

[@medcatmcat]

Hi! Great question. The question stem states that we cross two yellow flies from the F1 generation, so we can only look at the three cells of the first Punnett square (since the fourth square, ww, would be a white fly). Given our three genotypes in the cells (1 WW and 2 Ww), only a cross between two heterozygote yellow flies would yield an F2 generation that has both yellow and white flies. Since 2/3 of our yellow flies in the F1 generation are heterozygotes, the probability of our F2 generation being the result of two of these yellow flies mating is (2/3)*(2/3). For further explanation, I state why we use thirds instead of fourths at 5:25. I hope that helps! Let me know if you have any more questions.

[@strongbodystrongmiind]

@@medcatmcat Ehhh still kind of confused on the wording.. If big W means yellow, why are you saying "2/3 of our white flies in the F1 generation are hetero".... Shouldn't you be saying 2/3 of the yellow flies are hetero??

[@medcatmcat]

@@strongbodystrongmiind Yep! Just fixed that wording, thanks!

[@growthmedia97]

I am still confused on why you used 2/3 the second time

[@alexandria6192]

@@growthmedia97 hmm maybe I can stab at this. The question is asking what is the probability where both yellow and white progeny will happen in F2 generation. Knowing that your only genotypes are: WW or Ww or ww, the only cross that will yield both yellow AND white progeny has to come from a Ww x Ww cross. You need to back track and find the probability from F1 and F2 that would give you a Ww x Ww cross. Sooo when you actually do a punnet square for F1 (see video), you get 2/3 that are Ww that are yellow ... then when you do another punnet square for F2, you get a similar result of 2/3 that are Ww that are yellow ... so you multiply (2/3)*(2/3) ...don't get confused by the 'ww' in the punnet squares on your paper which is what I did the first time.

[@strongbodystrongmiind]

haha literally just came across this on AAMC

[@medcatmcat]

Well now you know it's truly AAMC-derived 😎

[@gillianramirez]

So if it said we're choosing one yellow and one white fly would it be (1/4)x(2/3)?

[@medcatmcat]

If I understand your question correctly, it would be (1)x(2/3) to find the probability, since we know for a fact that the genotype of whatever white fly we pick would be ww (homozygous recessive)-so probability = 1. Does that make sense?

[@Malin39up]

@@medcatmcat Hi, is her qn is 'if 1 yellow and 1 white fly is crossed, what is the chance that the F2 gen would contain both yellow and white flies?', why isn't it (2/4) x (1/4)? My thinking is - (2/4) bc there's two Ww in the first punnet square out of 4, and and (1/4) cus only one ww out of the 4. I'm confused! Pls help!!