Punnett Squares

Punnett Squares

Originally designed by Reginald Punnett

Genotype - this is the genetic makeup of the organism

• heterozygous - different alleles

• homozygous - same alleles

Multiple Choice

Heterozygous or homozygous?

BB

• heterozygous

• homozygous

Multiple Choice

Heterozygous or homozygous?

Bb

• heterozygous

• homozygous

Multiple Choice

Heterozygous or homozygous?

bb

• heterozygous

• homozygous

Phenotype - the physical appearance of the organism

• Think "ph" in phenotype and "ph" in physical

Multiple Choice

Genotype or phenotype?

• genotype

• phenotype

Multiple Choice

Genotype or phenotype?

Bb

• genotype

• phenotype

How to draw a Punnett Square...

• Find the genotype for each parent.

• Draw a 2 x 2 square

• The male parent goes at the top.

• The female parent goes along the left side.

• Bring the male letters down.

• Bring the female letters across.

Remember for a recessive trait to be expressed, both genes must be recessive.

All recessive traits would come from homozygous alleles.

Remember for a dominant trait to be expressed, the alleles can be heterozygous or homozygous.

You only need one dominant allele for a dominant trait to show up.

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