The method that scientist use today to predict the traits of offspring is called the Punnett Square method. This method was introduced by Reginald Punnett, who was an early 20th-century scientist. The diagram gives the probability of outcome when the allele from the mother crosses with the allele from the father.
The Punnett square is a graphical way of finding all the potential combinations of genotypes that can occur in a child.
Setting up and using a Punnett Square is very simple, once you understand how it works and how to properly place the allele on the grid.
The Punnett square is a graphical way of finding all the potential combinations of genotypes that can occur in a child.
Setting up and using a Punnett Square is very simple, once you understand how it works and how to properly place the allele on the grid.
1) We begin by drawing a grid
2) Next, you put the genotype of one parent across the top of the grid, and the other parent down the left side. In example, A father genotype for height is TT and a mothers genotype for height is Tt.
Note on good practice: Notice only one letter goes in each box for the parents. Also, it does not matter which parent is on the top or side of the square.
Note on good practice: Notice only one letter goes in each box for the parents. Also, it does not matter which parent is on the top or side of the square.
3) Finally, all you do is fill in the boxes by copying the row and column letter into the appropriate box.
Results: The probability of the offspring represented in this Punnett Square is 50% for a homozygous gene (TT) and 50% for a heterozygous gene (Tt). Because (T) is a dominant trait, there is a 100% chance the offspring will be TALL.
LETS PRACTICE !
Now we know that the outcome of a Punnett Square gives us the predicted frequency of all the potential genotypes among the offspring every time reproduction occurs.
Take out a piece of paper and do the practice problem below. If you get stuck go to the top of the page and review the lesson. When you finish the problem, show your teacher your answer. Good Luck !
Practice Problem: Parent #1 has a dominate homozygous trait for brown eyes (B) and Parent #2 has a heterozygous genotype (Bg). What is the probability that their child will have green eyes ?
B- Brown eyes
g- Green eyes
Think you mastered Punnett Squares ? Click on this link for more practice.
B- Brown eyes
g- Green eyes
Think you mastered Punnett Squares ? Click on this link for more practice.