When it comes to Punnett Squares in MCAT Genetics, that last thing you want to do is write out a complete 4 square or 16 square diagram for a Monohybrid or Dihybrid Cross. However, without the diagram you may find yourself unable to calculate phenotype or genotype percents or ratios.
That's why I've put together this detailed guide to Punnett Square values. Study the drawings for the sake of UNDERSTANDING then memorize the logic behind every ratio. This is how you ensure that you get it, retain it, and know how to use it during your MCAT without wasting precious time.
Click the image below to print/download the full version
I am watching your youtube videos from nearly a month.
It was soo intresting and help full.
Actually I am preparing for Mcat Entry test which is going to happen on 28th October.
Well thankyou.
Thank you very much Leah for these compact summarized notes.
What is ment by cheat seets
Wonderful examples. Thank you.
You’re welcome, Glen!
i might be missing something, but i think this strategy becomes very challenging to implement when there is overlap between sets. for example, say we have a cross AaBb x Aabb for which a disease is caused by subset {aa} or by subset {BB, Bb, bB}.
When know that Aa x Aa –> p(aa) = 1/4 and that Bb x bb –> p(BB, Bb or bB) = 1/2. But does p(“disease”) = 1/4 + 1/2 = 3/4? NO! When looking at at the full punnet square it becomes apparent that we also have to consider P({aa} and {BB, Bb, bB}) = 1/8. Thus, p(“disease”) = 1/4 + 1/2 -1/8 = 5/8. How can you quickly figure out P({aa} and {BB, Bb, bB}) without writing out a full punnet square? Maybe binomial theorem? In any case, it seems quicker to just write out the collum and row labels for the full 4×4 square, then circle and sum the areas of the square where you know disease will occur. You don’t actually need to fill in the square.