MathBench > Probability

More Mice with Fangs: Intermediate Punnett Squares

Ms. Heterozygote meets Mr. Recessive...

This time mom is a heterozygote -- she looks normal, but she's hiding one copy of each of the recessive genes. She takes a walk on the wild side, and mates with a dad who shows both of the recessive traits

Again, think for a moment about what to expect....

Did you think about it? Here's what I think: Dad will always contribute the same sperm: tf. So in a sense, mom controls the outcome. One-quarter of the offspring will look like each of mom's 4 possible egg types.

Now try the Punnett Square:

As predicted above, the ratio of normal:fluffy:vampire:both came out to 4:4:4:4, or one-quarter for each phenotype.