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How to do Punnett Squares?

We’re learning how to do Punnett squares in biology and I’m totally lost. How do you know when the letters are capitalized or lowercase? And how do you know what square to put the letters in?

This one questions says “Draw a Punnett square to show what genes a child would be expected to have if each parent were heterozygous for long eyelashes.” But again, I don’t know where to put the letters and I get which genes are dominant and recessive, but where do the letters go? Does dominant go on the top? Ugh! This is so confusing!

Help would be majorly appreciated! Thanks!

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Answer #1

a punnet square where the parents are both heterozygous for the gene would look something like this

    L           l

L LL Ll

l Ll ll

each parent has two alleles for the gene so write in the two possibilities on the top and the sides then just combine them to get four combinations of two alleles. Hope that makes sense. I know what you mean by does the dominant go on top. The alleles from each parent should be in the same place for each parent (as in, both alleles on the top, or both on the side, according to which parent they are from, not whether they are dominant or recessive).

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