7D61 Punnett Square

Background Parents contribute half their genes to each offspring, and coin tosses can model the way genes are passed on to offspring of 2 parents. A table called a Punnett Square can also help predict the results of a breeding experiment.

Using Punnett Squares Punnett Squares show how likely the outcome of a breeding experiment is. It is used when each parents’ genes for a trait are known. By filling in the squares you can find all the possible combinations of genes in offspring of two parents. You can also predict the chances that each kind of offspring will occur.

Skye and Poppy The critters Skye and Poppy had 2 versions of the tail-color gene, 1 for blue & 1 for orange. These two versions are called ALLELES. The blue allele is written as a capital T and the orange allele as lowercase t. This is because we know that blue tail color is dominant.

Alleles Skye is from an island with no orange-tail critters so he has only blue tail-color alleles, like TT. Poppy is from an island with no blue-tail critters so she has only orange tail-color alleles, like tt. Organisms with only one kind of allele for a characteristic are called HOMOZYGOUS. So Skye is homozygous for blue tail-color trait and Poppy is homozygous for orange tail-color trait.

Starting A Punnett Square Write the possible alleles from each parent at the top and left side of the table; it does not matter which parent you put in each position. In our table, Skye’s alleles are placed along the top and Poppy’s at the left. Each T at the top represents an allele in the sperm cell from Skye, while each t on the left represents an allele in the egg cell from Poppy.

Completing A Punnett Square Complete each box of the table by combining one allele from the top and one allele from the left, as shown on the table. When you combine one allele from each parent into a box, you are representing a sperm cell fertilizing an egg cell.

Making Conclusions All the offspring of Skye and Poppy will have one blue tail-color allele and one orange tail-color allele. An organism that has alleles for two different traits is called HETEROZYGOUS. Because blue tail-color is dominant over orange, all offspring will have blue tails as was found in the breeding experiment between Skye and Poppy.

7D61 Punnett Analysis: paragraphs Compare your Punnett Square results here for Problem 1 with the D59 coin toss. Explain. A. On page D36, what are the pea flower color traits? Suggest letters for those alleles. B. What are the seed surface traits? Suggest letters for those alleles. Review your Punnett Square results. Why is it impossible for offspring to show a recessive trait if one parent is homozygous dominant?