11-2 Probability and Punnett Squares - PowerPoint PPT Presentation

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11-2 Probability and Punnett Squares

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Mendel realized that the principles of probability could be used to explain the results of genetic crosses. He repeated a particular cross and obtained the same results. – PowerPoint PPT presentation

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Title: 11-2 Probability and Punnett Squares


1
11-2 Probability and Punnett Squares
2
Mendel realized that the principles of
probability could be used to explain the results
of genetic crosses.He repeated a particular
cross and obtained the same results.
3
Probability
  • The likelihood that a particular event will occur

4
A coin flip
  • Possible outcomes
  • Heads
  • Tails
  • Either outcome are equal.

5
One coin flip, makes 1 chance in 2This is ½ or
50
6
The probability of flipping three heads in a row
  • ½ X ½ X ½ 1/8
  • 1 chance in 8 flips

7
The principle of probability can be used to
predict the outcome of genetic crosses.
8
Punnett Square
  • The gene combinations that might result from a
    genetic cross.

9
F1 Parents are shown along the top and left side
of the square.
It also contains the possible gene combination
for F2 offspring and the allele
10
The punnett square can be used to predict and
compare the genetic variations that will result
from a cross.
11
Homozygous
  • Organisms that have two identical alleles for a
    particular trait TT or tt.
  • Org. for true breeding in particular trait

12
Heterozygous
  • Organisms that have two different alleles for the
    same trait. Tt
  • Organisms are hybrid for a particular trait.

13
Phenotype
  • Plants have the same physical characteristics.

14
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15
Genotype
  • Genetic makeup,
  • Genotype of one third of the tall plants is TT
  • Two thirds of the tall plant is Tt.

16
Plants have the same phenotype but different
genotype.
What would happen if you cross this two plants?
Short or Tall??
17
T t
T TT 25 Tt 25
T TT 25 Tt 25
18
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19
Probability and Segregation
  • ¼ of the F2 plants have two alleles for tallness
  • 2/4 or ½ have one allele for tallness
  • ¼ one allele for shortness
  • ¾ are going to be tall and ¼ short
  • Ratio 31

20
Predicted Ratio
  • For each seven crosses ¾ of the plants showed the
    trait controlled by the Dominant.
  • ¼ showed the trait controlled by the recessive
    allele.

21
  • The larger the number of offspring, the closer
    the resulting number will get to expected values.

22
Homework
  • To turn in
  • Make a punnett square with your family.
  • Use only one trait, like eye color, tallness,
    skin color, etc.
  • Add pictures to illustrate.

23
T t
t Tt 25 tt 25
t Tt 25 tt 25
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