11-2 Probability and Punnett Squares photo credit: W. Perry Conway/CORBIS Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

Beyond Dominant and Recessive Alleles What inheritance patterns exist aside from simple dominance? Copyright Pearson Prentice Hall

Beyond Dominant and Recessive Alleles Some alleles are neither dominant nor recessive. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

Beyond Dominant and Recessive Alleles RR 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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

X Co-Dominance White Chicken: Genotype = WW Black Chicken: Genotype = BB White Chicken: Genotype = WW X Speckled Chicken: Genotype = BW Copyright Pearson Prentice Hall