GeneticsPunnett Squares

Punnett Squares• Punnett squares are a way to look at

the gene pairs an offspring will inherit from their parents. It shows the probability of each match.• For example: Say you are looking at the

trait for height. T is the letter that represents the dominant trait for tall

• t is the letter that represents the trait for being short

Punnett Squares• If you were looking at the gene pairs

for a mother and father it might look like this:• Mother = Tt (one allele for tallness, one

for short)• Father = tt (both alleles are for short)• To see what the possible combinations

of offspring would be you would set up a punnett square.

T (mother) t (mother)t (father) Tt tt

t (father) Tt tt

1. Put the 2 alleles for the 1st parent in the top two boxes

(right justified)2. Put the 2 alleles for the 2nd parent in the left side

boxes (the top left corner box should be empty)

3. Carry the alleles down into the 2 squares below the 1st parent

4. Carry the alleles across into the 2 squares to the right of the 2nd parent

5. The 4 geneotypes inside squares are the possible offspring

Punnett SquareT t

t Tt ttt Tt tt

In the above example:•Two of the possible geneotypes would be the dominant trait for Tall (Tt) (one of the alleles is dominant and one is recessive also known as heterozygous)•Two of the possible geneotypes would be the recessive trait for SHORT (tt) (both of the alleles are the same also known as homozygous recessive)

Mother = Tt Father = tt

Punnett SquaresMother = WWFather = WwW = widows peakw = no widows

peak

W W

W WW WW

w Ww Ww

In the example: Two possible offspring would be heterozygous (Ww)

Two would be homozygous dominant (WW)

All four possible geneotypes would be the dominant trait for Widows Peak (WW) and (Ww)

PUNNETT SQUARE PRACTICE!

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