2. How to Solve a Punnet Square Notes

3. 1. Determine the genotypes (letters) of the parents
1. Determine the genotypes (letters) of the parents. Ex: Two mice are heterozygous for brown fur. Brown fur is dominant to white fur.
So the genotypes of the parents are Bb x Bb

4. 2. Set up the punnett square with one parent on each side.B b b B

5. 3. Fill out the Punnet square middleB b b B b b b B b B B B

6. 4. Analyze the number of offspring of each type.
List possible genotypes: 2Bb, 1BB, 1bb
List possible phenotypes: 3/4 brown fur (75%) and ¼ white fur (25%) B b
*Results could be in percent (25%), ratio (1:4) or pfractions (1/4). b B b b b B B b B B

8. RR = round Rr = round rr = wrinkled
In pea plants, round seeds are dominant (R) to wrinkled(r). The genotypes and phenotypes are:
RR = round Rr = round rr = wrinkled
If a homozygous round seed is crossed with a heterozygous round seed, what are the possible genotypes and phenotypes?

9. If a homozygous round seed is crossed with a heterozygous round seed, what are the possible genotypes and phenotypes? R R R R R R R R r r R r

10. Genotypes: Phenotypes:
2RR, 2Rr
4/4 or 100% Round

11. : In radishes, a bent root is a dominant trait, though some roots are straight (which is recessive). If a straight rooted plant is crossed with a heterozygous bent root plant, how many of the offspring will have straight roots?
*HINT: Start by assigning genotypes and phenotypes. Pick the letter of the dominant trait. B for bent
BB = bent Bb = bent bb = straight
Now use the key to figure out your parents. In this case you have a straight root plant crossed with a heterozygous bent plant. Once you've figured that out, the cross is simple!

12. bb x Bb (or bB) b B b B b b b b b b B b

13. Genotypes: Phenotypes:
2Bb, 2bb
2/4 or 50% Bent, 2/4 or 50% straight