1. and How to use a Punnett Square to predict probable offspring
Medelian Genetics
and
How to use a Punnett Square
to predict probable offspring

2. Simple Steps to follow
1. Determine the parental phenotype and genotypes of the traits being crossed.
2. Determine the possible gametes from the parents in #1.
3. Use the gametes to fill the outside of a blank Punnett Square.
4. Complete the inside of the Punnett Square.

3. More Steps…
5. Count the number of possible genotypes found in the Punnett Square.
6. Determine the percentage of genotypes found.
7. Determine the phenotypes (based on the genotypes) and percentages from the Punnett Square.
8. Celebrate – you’re done!

4. Example. . . Oompah Loompah Genetics

5. Who/What are Oompah Loompahs?

6. Phenotype = Face Color (F) Dominant = Recessive = BLUE ORANGE
Step 1.
Phenotype = Face Color (F)
Dominant = Recessive =
BLUE ORANGE
Genotype = Genetic make-up
FF or Ff ff
Dad
Mom

7. Step 2 . Determine possible gametes
Genotype = ff
Genotype = FF or Ff
Gamete = f
Gamete = F F or f
Let’s use the heterozygous dad to find out what possible offspring they might have.

8. Step 3. Fill in gametes outside of Punnett Square
Mom f f F f
Dad

9. Step 4. Fill in inside of Punnett SquareFf Ff ff ff

10. Step 5. Count the number of possible offspring genotypes found in the Punnett Square.
2 out of 4
= 50% f F Ff ff
2 out of 4
ff =
= 50%
Step 6: Determine percentages - done above!

11. Step 7. Determine offspring phenotypes and percentages
Genotypes are:
Ff = 2/4 = 50% and ff = 2/4 = 50%
Phenotypes are:
Ff = BLUE face = 2/4 = 50%
ff = ORANGE face = 2/4 = 50%

12. Summary
Crossing a blue face Oompah Loompah with an orange face Ompah Loompah may produce 50% blue-faced children and 50% orange-faced children

13. Make Sense???
Try the Oompah Loompah worksheet!