MathBench > Probability

Mice with Fangs: Intro to Punnett Squares

One more time...

What you just did is called a di-hybrid cross. The mice were ‘di-hybrids' because they were hybrid for both teeth and fur. And you crossed them (which is an interesting way of saying you, um, convinced them to mate). So, a dihybrid cross.

xray gogglesLet's try another dihybrid cross. Let's see, what traits can we manipulate? I encourage you to come up with your own interesting combinations (and illustrations) but in case you're drawing a blank, I'll propose one: the di-hybrid superhero cross. The first gene pair (X and x) gives the lucky recipient x-ray vision (recessive) vs. normal eyes (dominant). The second gene pair (B and b) gives the recipient bat-like flight (recessive) vs. normal locomotion (dominant). Our two parents are Mr. and Mrs. Normal. They look normal, but actually they are both di-hybrids, with one copy of each allele. Draw a Punnett Square to determine whether any of their children will become superheros (flying or x-ray), and whether any will become super-superheroes with both traits. Remember to put Mom's contributions on the top of the square and Dad's on the left side.

(If you are lazy like me, you probably don't want to go to all that trouble again, so after you do Mom and Dad, you can click on 'Fill in kids')

Hey, there's that 9:3:3:1 ratio again. Coincidence? I think not!

photo credits: goggles | bats