1. 11-2 Probability and Punnett Squares
photo credit: W. Perry Conway/CORBIS
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2. Punnett Squares
Punnett Squares
The gene combinations that MIGHT result from a genetic cross can be determined by drawing a diagram known as a Punnett square.
Punnett squares can be used to predict and compare the genotypes of the offspring.
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3. T = tall. (Dominant) t = short. (Recessive) Punnett Squares
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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4. Gametes produced by each parent are shown along the top and left side.
Punnett Squares
Gametes produced by each parent are shown along the top and left side.
Possible gene combinations for the F2 offspring appear in the four boxes.
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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5. What are the Phenotypic results for the new generation?
Punnett Squares
What are the Phenotypic results for the new generation?
Tall: ________
Short: ________
What are the Genotypic results for the new generation?
TT: ___ Tt __ tt __
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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6. Beyond Dominant and Recessive Alleles
What inheritance patterns exist aside from simple dominance?
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7. Beyond Dominant and Recessive Alleles
Some alleles are neither dominant nor recessive.
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8. Beyond Dominant and Recessive Alleles
Incomplete Dominance 
When one allele is not completely dominant over another it is called incomplete dominance.
In incomplete dominance, the two alleles mix.
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9. Beyond Dominant and Recessive AllelesRR
A cross between red (RR) and white (WW) four o’clock plants produces pink-colored flowers (RW). WW
Some alleles are neither dominant nor recessive. In four o’clock plants, for example, the alleles for red and white flowers show incomplete dominance. Heterozygous (RW) plants have pink flowers—a mix of red and white coloring.
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10. Beyond Dominant and Recessive Alleles
Codominance 
In codominance, both alleles are shown.
In certain varieties of chicken, the allele for black feathers is codominant with the allele for white feathers.
Heterozygous chickens are speckled with both black and white feathers. The black and white colors do not blend to form a new color, but appear separately.
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11. X Co-Dominance White Chicken: Genotype = WW
Black Chicken: Genotype = BB
White Chicken: Genotype = WW X
Speckled Chicken: Genotype = BW
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