Punnent Square

THE PUNNETT SQUARE

The Punnett square is an easy way to demonstrate the possibilities of a single inheritable trait being present in an offspring. For each Punnett Square, replace the question marks (??) with the appropriate information to correctly complete the square. Respond to the questions that relate to each square.

In the Punnett square below, it is evident that there is equal opportunity for the fertilized egg to develop into either a boy or girl (XX=Female; XY=Male).

X Y

X

XX

XY

X

XX

XY

Try two examples for yourself. Brown eyes are dominant over blue eyes. Complete the square using the letter "B" (for the dominant trait of brown eyes) and "b" (for the recessive trait of blue eyes) to determine the probability of having a child with blue eyes.

B b

B

BB

Bb

b

Bb

bb

____25___% chance of having a blue eyed child

B B

b

bB

bB

b

bB

bB

___0_% chance of having a blue eyed child.Now do the Punnett square to represent two people who are both carriers of a recessive disorder (A carrier is someone who has just one copy of the recessive gene. They do not have the disorder but could pass the recessive gene to their offspring). You need to provide each parent's genetic make-up and the four possible gene combinations that could occur in their child.

C b

A

AC