6: 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

  • mom is TtFf
  • dad is ttff

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.