1. 11-2 Probability and Punnett Squares
photo credit: W. Perry Conway/CORBIS
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2. Genetics and Probability
The likelihood that a particular event will occur is called probability.
Let’s consider a coin toss.
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3. probability can be used to predict the outcomes of genetic crosses.
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Punnett Squares
Punnett Squares
Offspring can be determined by a Punnett square.
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Punnett Squares
A capital letter represents the dominant allele for tall.
A lowercase letter represents the recessive allele for short.
In this example,
T = tall
t = short
The principles of probability can be used to predict the outcomes of genetic crosses. This Punnett square shows the probability of each possible outcome of a cross between hybrid tall (Tt) pea plants.
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Punnett Squares
Gametes produced by each F1 parent are shown along the top and left side.
The principles of probability can be used to predict the outcomes of genetic crosses. This Punnett square shows the probability of each possible outcome of a cross between hybrid tall (Tt) pea plants.
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Punnett Squares
Organisms that have two identical alleles for a particular trait are said to be homozygous (TT or tt).
Organisms that have two different alleles for the same trait are heterozygous (Tt).
Homozygous organisms are true-breeding for a particular trait.
Heterozygous organisms are hybrid for a particular trait.
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Punnett Squares
All of the tall plants have the same Phenotype, or Physical characteristics.
The tall plants do not have the same Genotype, or Genetic makeup.
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9. The genotype of one third of the tall plants is TT,
While the genotype of two thirds of the tall plants is Tt.
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Punnett Squares
These plants have different genotypes (TT and Tt), but they have the same phenotype (tall).
Although these plants have different genotypes (TT and Tt), they have the same phenotype (tall). TT
Homozygous Tt
Heterozygous
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11-2
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11-2
Two F1 plants that are homozygous for shortness are crossed. What percentage of the offspring will be tall?
100%
50% 0%
25%
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11-2
The Punnett square allows you to predict
only the phenotypes of the offspring from a cross.
only the genotypes of the offspring from a cross.
both the genotypes and the phenotypes from a cross.
neither the genotypes nor the phenotypes from a cross.
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14. END OF SECTION