in this chapter, i'll be explaining how to use punnett squares! but first:
what is a punnett square?
a punnett square is a table used to determine the likelihood of the offspring of two individuals having certain traits
what are alleles, and how do they work?
alleles are different variants of a gene. when using a punnett square, these are shown using capital and lowercase letters. for each gene, an animal has two alleles. dominant alleles are always written in capital letters (like this: B), and recessive alleles are written as lowercase (like this: b). when written, the dominant allele always goes before the recessive one (Bb) if there is one of each. this means the dominant allele will be the one that shows on the animal, not the recessive one. when these alleles are passed down, the offspring receive one allele from each parent. for example, if the mother's alleles are "BB", and the father's are "bb", the offspring's alleles would be "Bb", and the offspring would be the dominant gene, but carry the other one.
how to use a punnett square?
so first, we start with a 3 x 3 table, like this:
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lets say for our example that we are working out if a cat is black or chocolate (brown). BB - black Bb - black, carrying chocolate bb - chocolate
now, you put in the parent's alleles. it doesn't really matter what order you do it in, but generally the father's alleles go in the top boxes, and the mother's in the left ones.
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in this example, the father's alleles (BB) are homozygous dominant, meaning they are both dominant alleles. And the mother's (Bb) are heterozygous, meaning they are different (one dominant and one recessive allele).
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Now we calculate the possible outcomes by combining the letters from the top and bottom in the other four boxes.
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so, we end up with:
50% homozygous black (just black) 50% heterozygous black (black carrying chocolate)
notes.
─ alleles will always be ordered with the dominant one (the capital letter), first. like this: B/b.
hopefully i explained that well enough! if you want more examples, or if you have questions, please tell me in the comments! :)
