Punnett Square Review

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Punnett Square Review
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Mendels Laws of Inheritance

• Law of Dominance In heterozygous genotypes,
  dominant alleles hide recessive alleles when both
  are inherited by an organism. (Hh means the
  dominant trait will show up in the phenotype)

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Mendels Laws of Inheritance
1. The Law of Segregation (separation) Each
organism has 2 alleles for a gene. Only one
allele from each gene 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

• T tall

• What letters would you use to represent this
  cross?

• 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

• Recessive trait white hair

• B brown

• b white

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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

• Genotype
• BB
• Bb
• bb

0
b b
50
Bb
Bb
B b
50

• 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

• Recessive trait short hair

• L long

• l short

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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

• Genotype
• LL
• Ll
• ll

50
L l
50
LL
Ll
L L
0

• Phenotype
• long
• short

100
LL
Ll
0
10

• 4. Cross a heterozygous wrinkly elephant with
  another heterozygous wrinkly elephant.

• What letters would you use to represent this
  cross?

• Dominant trait wrinkly skin

• Recessive trait smooth skin

• W wrinkly

• w smooth

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• What is the genotype of a heterozygous
  wrinkly-skinned elephant?

• Ww

• What is the genotype of a heterozygous
  wrinkly-skinned elephant?

• Ww

• Ww x Ww

• Genotype
• WW
• Ww
• ww

25
W w
50
WW
Ww
W w
25

• Phenotype
• 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

• Genotype
• RR
• Rr
• rr

50
R r
50
RR
Rr
R R
0

• Phenotype
• round
• wrinkled

100
RR
Rr
0
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Mendels Laws (cont.)

• The Law of Independent Assortment Alleles for
  different genes separate independent of each
  other.

Yellow Round x Green Wrinkled
Parents
rryy
RR YY
x
To find the genotype for 4 alleles, use the FOIL
method to determine each parents alleles for the
cross
RR YY
All offspring (babies) will have a genotype of
RrYy
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Self-pollinate the offspring
RrYy
RrYy
x
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
Ry
RrYY
RrYy
rrYY
rrYy
rY
ry
RrYy
Rryy
rrYy
rryy
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• Genotype
• RRYY
• RRYy
• RrYY
• RrYy
• RRyy
• Rryy
• rrYY
• rrYy
• rryy

• Phenotype
• yellow round
• green round
• yellow wrinkled
• green wrinkled

56.3
50
18.8
50
18.8
0
6.3
50
50
0
50
50
0
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• What is the probability of getting a yellow round
  offspring?
• What is the probability of getting a green round
  offspring?
• What is the probability of getting a yellow
  wrinkled offspring?
• What is the probability of getting a green
  wrinkled offspring?

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• Exceptions to Gregor Mendels Laws

• Multiple Alleles Three or more forms of a gene
  that code for a single trait. (Not just two)

• Linked Genes Genes found on the same
  chromosome that travel together. The closer
  together on the chromosome they are, the more
  likely they will travel together. Ex In fruit
  flies the genes affecting eye color and wing
  length are inherited together because they appear
  on the same chromosome.

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• What do you think happens if 2
• alleles are equally strong?

• Incomplete dominance occurs

• This is when 2 alleles are neither dominant nor
  recessiveneither of the two alleles in a gene
  pair masks/hides the other.

• The result is a complete blending of traits,
  because neither one is stronger than the other.

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• How do we represent the genotypes of incomplete
  dominance traits?

• We use all CAPITAL LETTERS

4 Oclock Flowers

• If we cross breed a pure purple flowering plant
  with a pure white flowering plant, what would be
  the resulting offspring?

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• What is the genotype of a pure purple flowering
  plant?

• PP

• What is the genotype of a pure white flowering
  plant?

• WW

• PP x WW

• Genotype
• PP
• WW
• PW

0
W W
0
PW
PW
P P
100

• Phenotype
• Purple
• White
• Lavender

0
PW
PW
0
100
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• How would you represent an incomplete dominance
  cross between a pure red flower and a pure yellow
  flower?

Work this example of Incomplete Dominance in your
notes using our 4 oclock example to help you.
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• What is the genotype of a pure red flowering
  plant?

• RR

• What is the genotype of a pure yellow flowering
  plant?

• YY

• RR x YY

• Genotype
• RR
• YY
• RY

0
Y Y
0
RY
RY
R R
100

• Phenotype
• Red
• Yellow
• Orange

0
RY
RY
0
100
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• What is the genotype of a hybrid orange flowering
  plant?

• RY

• RY x RY

• Genotype
• RR
• YY
• RY

25
R Y
25
RR
RY
R Y
50

• Phenotype
• Red
• Yellow
• Orange

25
RY
YY
25
50
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• PURE GOLD

Breeding a pure brown with a pure white

• BB x WW

• Genotype
• BB
• WW
• BW

0
W W
0
BW
BW
B B
100

• Phenotype
• Brown
• White
• Palomino

0
BW
BW
0
100