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More possible examples of single gene combinations:

Aa x AA where Aa = female alleles and AA = male alleles

Half of the possible offspring have the same allele combination; AA homozygous dominant and the other half have the Aa heterozygous combination.

Probability calculations are: two out of four possible combinations create 50% chance for AA, and 50% chance for Aa alleles.

There is a ratio of 1:1

Ee x Ee where Ee = female alleles and Ee = male alleles

There are three different offspring combinations. One is EE (homozygous dominant), two are Ee (heterozygous) and one is ee (homozygous recessive).

Probability calculations are: one out of four possible combinations create 25% chance for EE, two offspring create a 50% chance for the Ee alleles, and finally 25% chance for the ee alleles.

This can be shown simply as:

EE - 25%

Ee - 50%

ee - 25%

The probability values must add up to 100% (25 + 50 + 25 = 100)

The ratio can be summarised as 1: 2 : 1.

Using the worked example to help you, work through the additional examples below.

Step 1:

Female: Aa Male: Aa

Step 2: Aa x Aa

Step 3:

Step 4: Female: A and a

Male: A and a

Step 5:

Step 6:

Allele letter choice select a letter that has a clearly different lower case, for example: Aa, Bb, Dd.

Method:

• Draw your Punnett square
• Add the alleles into your Punnett square around the edges
• Work out the new possible genetic combinations inside the Punnett square