Punnett Squares

1
Punnett Squares

• pp. 180-183

2

• Probability likelihood an event will happen and
  can be expressed as percentages, fractions, or
  decimals
• Monohybrid cross cross between individuals that
  looks at one trait
• Punnett square diagram to predict the
  probability of inheritance of certain traits

3

• Place the parent genotypes in
• Aa x Aa
• Match letters and fill in squares

Parent I
A
a


A
Aa
AA
Parent II
a
aa
Aa
4
MENDELS RATIOS
Genotype ratio- 1BB 2Bb 1bb 121
Phenotype ratio- 3 Black 1 Brown 31
5
Genotype ratio
22 or 1 1
Phenotype ratio
All black
6
TEST CROSS

• Cross the dominant phenotype with a homozygous
  recessive (bb)
• If you have recessive offspring then the
  individual must be heterozygous

Parent I
Parent I
b
b
b
b




B
Bb
Bb
B
Bb
Bb
Parent II
Parent II
B
b
Bb
Bb
bb
bb