Medelian Genetics

and

How to use a Punnett Square

to predict probable offspring

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.

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!

Example. . .Oompah Loompah Genetics

Who/What are Oompah Loompahs?

Oompah Loompah

Step 1.

Phenotype = Face Color (F) Dominant = Recessive =

BLUE ORANGE

Genotype = Genetic make-up Dominant = Recessive =

FF or Ff ff

Dad Mom

Step 2 . Determine possible gametes

Genotype = FF or Ff Genotype = ff

Gamete = F F or fGamete = f

Let’s use the heterozygous dad to find out what possible offspring they might have.

Step 3. Fill in gametes outside of Punnett Square

f f

F

f

Mom

Dad

Step 4. Fill in inside of Punnett Square

f f

F

f

Ff Ff

ff ff

Step 5. Count the number of possible offspring genotypes found in the Punnett Square.

f f

F Ff Ff

f ff ff

Genotypes:

Ff =

ff =

2 out of 4

2 out of 4

= 50%

= 50%

Step 6: Determine percentages - done above!

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%

Summary

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

Make Sense???

Try the Oompah Loompah worksheet!