Punnett Square

1
Punnett Square

• Learn how to complete
• a Punnett square.

2
Punnett Square

• Remember that each individual receives only one
  of the two possible genes for each genetic trait
  from each parent.

3
Punnett Square

• Example Dad may carry the genetic information
  for both brown eyes and blues eyes. He would be
  a brown-eyed heterozygote.

4
Punnett Square

• This phenotype information will be expressed as
  Bb capital B for Brown because it is a dominant
  trait, and lower case b for blue the recessive
  trait.
• Dad got this information from his parents. One
  B came in a gamete and the other b came in the
  other gamete. Remember that gametes are sex
  cells, egg or sperm.

5
Punnett Square

• Only one of those possibilities will be in a
  sperm when it is created during the meiosis
  process.

6
Punnett Square

• Mom may carry information for blue eyes only.
  This information will be placed in each egg that
  is created during the meiosis process.
• This phenotype information will be expressed as
  bb, because the recessive trait is the only
  genetic possibility that mom has.

7
Punnett Square Set-up

• The male information will be placed at the top of
  the Punnett Square and the female genetic
  information will be written along the left side.
  

8
Punnett Square Set-up

• Bring the genetic information from the male down
  to each box below it. Like so

B
b
B
b
9
Punnett Square Set-up

• Then bring the genetic information from the
  female across to each box on the right. Like so

B
b
b
b
B
b
b
b
10
Punnett Square Set-up

• Consider the possible results of this crossing.
  Two of the four possibilities will be Bb giving
  the 24 (read as two to four) ratio or 50
  probability.

B
b
b
b
B
b
b
b
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Punnett Square Set-up

• The Bb genetic information, genotype, will be
  expressed as a Brown phenotype. Phenotype is how
  the genetic information is expressed or seen.

B
b
b
b
B
b
b
b
12
Punnett Square Set-up

• The other possibility is that two of the four
  boxes have bb. This is also a 24 ratio with a
  50 probability. The resulting phenotype would
  be blue.

B
b
b
b
B
b
b
b