Genetic Probability

1
Genetic Probability

• Using Punnett Squares

Reginald Punnett
2
Review Vocab 9-1
3
Review - Alleles

• Dominant Alleles are represented by capital
  letters Yellow Seed Y)
• Recessive alleles are represented by lower case
  letters (green seed y)

4
Tracking Inheritance

• P Parental generation
• F1 First generation offspring
• F2 Second generation offspring
• Etc.

5
Determining The Offspring
Monohybrid Cross

• P Generation
• Female Tall plant (TT) is crossed with a Male
  short plant (tt)
• Set up is TT x tt
• Steps to take
• Determine the gametes
• Set up punnett squares
• Determine offspring ratios (phenotypic
  genotypic

6
Determining the Gametes

• Female is TT, what are the possible gametes?
• The female can pass on the 1st T or the 2nd T to
  the offspring.
• Possible gametes are T or T
• Male is tt, what are the possible gametes?
• Possible gametes are t or t
• What about Tt?
• Possible gametes are T or t

7
Setting Up The Squares

• Female gametes go on the top of the square
• Male gametes go on the side of the square

8
Filling In The Squares

• The letter on the top drop down to the boxes
  below.
• The letters on the side move over to the boxes on
  the right

T
T
T
T
T
T
t
t
t
t
t
t
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Determine Offspring Ratios

• F1 Generation
• Phenotypic
• Tall Short
• 4 0
• Genotypic
• TT Tt tt
• 0 4 0

T
T
t
T
t
t
T
t
T
t
T
t
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What about the next generation?

• F2 Generation allow F1 generation to
  self-pollinate
• Tt x Tt
• Determine gametes
• Female (Tt) gametes T or t
• Male (Tt) gametes T or t
• Set up punnett square

11
Filling In The Squares

• The letter on the top drop down to the boxes
  below.
• The letters on the side move over to the boxes on
  the right

T
t
T
t
T
t
T
T
T
t
t
t
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Determine Offspring Ratios

• F2 Generation
• Phenotypic
• Tall Short
• 3 1
• Genotypic
• TT Tt tt
• 1 2 1

T
t
T
T
T
t
T
t
T
t
t
t
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Your Turn

• Try the following crosses, complete a punnett
  square and determine ratios
• GG x gg
• Gg x gg
• Pure Tall plant vs Hybrid Tall Plant
• Heterozygous tall plant self pollinates

• Hints
• TT x Tt
• Tt x Tt

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Genetics - the study of heredity

• Heredity - Passing on of a trait
• Trait - Characteristic passed on via DNA
• Allele - piece of DNA carrying a trait

15
Gregor Mendel - Father of heredity

• Austrian Monk
• Worked with Pea Plants
• Looked at 7 different characteristics
• Was able to predict outcomes of genetic traits.

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Gregor Mendel - Father of heredity

• Dominant - Allele (DNA piece) is strong for a
  trait. Tall plant (TT, Tt)
• Recessive - Allele is weak for a trait. Short
  plant (tt)

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Genes inside and out

• Phenotype - What one physically looks like
  Example - Freckles
• Genotype - What your alleles say
  Example - FF or Ff for freckles
• Homozygous - 2 similar alleles for 1 trait Ex. FF
  or ff
• Heterozygous - 2 different alleles for 1 trait
  Ex. Ff

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Mendels Laws of Genetics

• Law of Segregation - Parent passes 1 of 2 alleles
  on for each trait
• Law of Independent Assortment - Genes are mostly
  inherited separately of each other

19
Test Crosses
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Quick Glance Dihybrid Cross

• Two traits are considered in a cross
• Example Yellow Round Seeds crosses with a Green
  Wrinkled Seeds
• Genotypes YYWW x yyww
• Offspring YyWw
• Self pollinate offspring YyWw x YyWw
• Determine gametes
• Set up Punnett Square

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Quick Glance Dihybrid Cross

• Gametes are YW, Yw, yW, yw

Y
w
W
W
Y
y
y
w
Y
Y
Y
Y
Y
Y
y
y
y
y
y
y
y
y
Y
Y
W
W
W
W
W
W
W
W
w
w
w
w
w
w
w
w




Y
W
Y
Y
Y
Y
W
W
W
W
Y
Y
Y
Y
Y
w
w
w
w
w
W
y
y
y
y
y
y
W
W
W
W
y
w
y
y
y
y
w
w
w
w
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Quick Glance Dihybrid Cross
Offspring Ratios

• Phenotypic
• Yellow Round Yellow Wrinkled Green Round
  Green Wrinkled
• 9 3
  3 1
• Genotypic
• YYWW YYww YYWw YyWW YyWw Yyww yyWw
  yyWW yyww
• 1 1 2 2
  4 2 2 1
  1

Just remember the phenotypic ratio!