Punnett Squares

1
Punnett Squares
2

• Defined Tool used to determine probability
• Probability likelihood that a certain event
  will happen
• 2 Steps
• 1) Place parent genotypes on the outside of the
  box
• 2) Fill in the boxes

Punnett Squares
3

• Cross a homozygous dominant yellow (YY) plant
  with a homozygous recessive green (yy) plant

• List the genotypes?
• 4Yy
• List the phenotypes?
• 4 Yellow
• Why will no peas be green in color?
• Yellow allele (Y) is dominant

y y
Y Y
Y
Y
y
y
Y
Y
y
y
4

• Cross a heterozygous dominant yellow (Yy) plant
  with a heterozygous dominant yellow (Yy) plant

• List the genotypes?
• 1YY, 2Yy, 1yy
• List the phenotypes?
• 3 Yellow, 1 green
• What is the probability of having a green plant?
• 1/4 or 25

Y
y
Y
Y
Y
Y
y
Y
y
y
y
y
5
What is the probability of having a

• homozygous recessive offspring?
• 1/4 or 25
• homozygous dominant offspring?
• 1/4 or 25
• heterozygous dominant offspring?
• 2/4 or 50
• yellow plant?
• 3/4 or 75

6
Cross a heterozygous normal (Nn) female with a
cystic fibrosis (nn) male
n n

• List the possible genotypes?
• 2Nn, 2nn
• List the possible phenotypes?
• 2 Normal,
• 2 cystic fibrosis

N
N
N n
n
n
n
n
n
n
7
What is the probability of having a

• homozygous dominant child?
• 0
• Homozygous recessive child?
• 2/4 or 50
• Cystic fibrosis child?
• 2/4 or 50
• child that is a carrier of CF?
• 2/4 or 50
• Would you like to know this if you were a parent?