Punnett Squares

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Punnett Squares
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Punnett Squares

• Illustrates how the parents alleles might
  combine in offspring.
• One parents alleles are placed down the side of
  the square, the other parents alleles are placed
  along the top

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• Heterozygous having different alleles for a
  hereditary character
• Homozygous having identical alleles for a
  heredity character

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Mendels Laws of Inheritance

1. Law of Dominance In heterozygous genotypes,
   dominant alleles hide recessive alleles when
   both are inherited by an organism.

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Mendels Laws of Inheritance
1. The Law of Segregation (separation) Each
organism has 2 alleles for a trait. Only one
allele from each pair will be passed on to the
offspring.
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Homozygous/Heterozygous
Hmzg / Htzg

• Cross a homozygous dominant tall plant with a
  homozygous recessive short plant.

• Dominant trait tall

• Recessive trait short

• What letters would you use to represent this
  cross?

• T tall

• t short

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• What is the genotype of a homozygous dominant
  tall plant?

• TT

• What is the genotype of a homozygous recessive
  short plant?

• tt

• TT x tt

• Genotype
• TT
• Tt
• tt

0
t t
100


Tt
Tt
T T
0

• Phenotype
• tall
• short

100
Tt
Tt
0
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• 2. Cross a heterozygous brown haired rabbit with
  a homozygous recessive white haired rabbit.

What letters would you use to represent this
cross?

• Dominant trait brown hair (B)

• Recessive trait white (b)

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• What is the genotype of a heterozygous brown
  haired rabbit?

• Bb

• What is the genotype of a homozygous recessive
  white haired rabbit?

• bb

• Bb x bb

• Possible Genotype(s)
• BB
• Bb
• bb

0
b b
50


Bb
Bb
B b
50

• Possible Phenotype
• brown
• white

50
bb
bb
50
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• 3.. Cross a homozygous dominant long haired
  guinea pig with a heterozygous long haired guinea
  pig.

What letters would you use to represent this
cross?

• Dominant trait long hair (L)

• Recessive trait short hair (l)

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• What is the genotype of a homozygous dominant
  long haired guinea pig?

• LL

• What is the genotype of a heterozygous long
  haired guinea pig?

• Ll

• LL x Ll

• Possible Genotype(s)
• LL
• Ll
• ll

50
L l
50


LL
Ll
L L
0

• Possible Phenotype(s)
• long
• short

100
LL
Ll
0
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• 4. Cross a heterozygous wrinkly elephant with
  another heterozygous wrinkly elephant.

• Dominant trait wrinkly skin (W)

What letters would you use to represent this
cross?

• Recessive trait smooth skin (w)

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• What is the genotype of a heterozygous elephant?

• Ww

• What is the genotype of a heterozygous elephant?

• Ww

• Ww x Ww

• Possible Genotype(s)
• WW
• Ww
• ww

25
W w
50


WW
Ww
W w
25

• Possible Phenotype(s)
• wrinkly
• smooth

75
Ww
ww
25
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A plant that is homozygous dominant for round
seeds is crossed with a heterozygous plant. What
is the probability that the offspring will have
wrinkled seeds?

• R round

• r wrinkled

RR x Rr

• Possible Genotype(s)
• RR
• Rr
• rr

50
R r
50


RR
Rr
R R
0

• Possible Phenotype(s)
• round
• wrinkled

RR
Rr
100
0