Punnett Squares

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Punnett Squares
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Phenotype and Genotype Practice

• 1. Describe the genotypes given. The first one is
  already done.
• Example DD homozygous, dominant
• A. ss ______________________
• B. Yy ______________________
• C. dd __________________
• D. Ww ____________________
• 2. In humans, brown eye color (B), is dominant
  over blue eye color (b). What are the phenotypes
  of the following genotypes? In other words, what
  color eyes will they have?
• A. BB ________________________
• B. bb ________________________
• C. Bb ________________________

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Punnett Squares

• Used to organize all the possible combinations of
  offspring from particular parents

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Making a Punnett Square

1. Draw a square divide it into four sections.

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Making a Punnett Square

• For this example, we will show the cross between
  two plants that produce round seeds.
• Rround seeds
• roval seeds

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Making a Punnett Square

• 2. Write the letters that represent alleles
  (genes) from one parent along the top of the box.

r
R


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Making a Punnett Square

• 3. Write the letters that represent alleles
  (genes) from the other parent along the side of
  the box.

R
r


R
r
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R
r


R
r
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R
r
RR Rr
Rr rr
R
r
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Example 1
G
G


G
g
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Example 2
A
A


a
a
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Probability

• The mathematical chance that something will
  happen.
• Example If you toss a coin, the probability of
  tossing heads is ½, or 50. You will get heads
  half the time.

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What is the probability of having a baby with
blue eyes?
B
b
BB Bb
BB Bb
B
B
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Example 1

• The allele for a cleft chin, C, is dominant among
  humans. Using a Punnett square, what are the
  results of a cross between parents with genotypes
  Cc and cc?
• What is the probability that the offspring will
  have a cleft chin?

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Example 2

• This Punnett square shows the alleles for fur
  color in rabbits. Black fur, B, is dominant over
  white fur, b.
• Given the combinations shown, what are the
  genotypes of the parents?

Bb Bb
Bb Bb
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Problem 1
?
?

1. What is the unknown genotype?
2. If T represents the allele for tall pea plants
   and t represents the allele for short pea plants,
   what is the phenotype of each parent and
   offspring?

TT TT
Tt Tt
T
t
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Problem 2

• The allele for freckles, F , is dominant among
  humans. Using a Punnett square, what are the
  results of a cross between parents with genotypes
  FF and ff?
• What is the probability that the offspring will
  have freckles?

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Whiteboard Practice Problems
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Greetings Scientists!!
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• In rabbits, black fur is dominant to white fur.
  If you cross a BB male with a Bb female, what are
  the possible genotypes and phenotypes of the
  offspring? What is the percent chance for each
  type?

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• In cabbage butterflies, white wings are dominant
  to yellow wings. If a Ww butterfly is crossed
  with a ww butterfly, what are the possible
  genotypes and phenotypes of the offspring and the
  percent chance for each?

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• In dogs, there is a hereditary type of deafness
  caused by a recessive gene. Two dogs who carry
  the gene for deafness but have normal hearing are
  mated. What are the possible genotypes and
  phenotypes of their offspring and the percent
  chance for each?

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• In guinea pigs, short hair is dominant over long
  hair. If a short haired SS guinea pig is crossed
  with a long haired ss guinea pig, what are the
  possible genotypes and phenotypes of their
  offspring and the percent chance of each?

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• Can you curl your tongue up on the sides?
  Tongue-curling in humans is a dominant genetic
  trait. Suppose a man who is Tt for tongue-curling
  marries a woman who is also Tt for this trait.
  What are the possible genotypes and phenotypes of
  their children and the percent chance for each?