For some traits, one allele is not completely dominant to another. Incomplete dominance occurs when neither allele dominates over the other. The resulting phenotype of heterozygotes is an intermediate of the two extremes. Incomplete dominant genes control snapdragon flower color. Red flower plants crossed with white flower plants produce offspring with pink flowers. One human trait that is thought to be inherited in this fashion is hair structure. Curly hair and straight hair are due to homozygous genotypes and wavy hair is produced by the heterozygous genotype. An incompletely dominant gene also controls the plumage of chickens. Black plumage and white plumage are due to homozygous genotypes and a blue-grey color results from a heterozygous genotype. Using Punnett squares and variations of the letter “B”, answer questions 1-3 and use variations of the letter “R” to answer questions 4-5. What type of offspring and in what ratio would you expect from a cross between a black and a white chicken? What type of offspring and in what ratio would you expect from a cross between a black and a grey chicken? 3. What type of offspring and in what ratio would you expect from a cross between two grey chickens? 4. Cross a pure-line red (R) snapdragon flower with a pure-line white (r) snapdragon. What are the possible genotypes? 5. Cross two pink snapdragons. What are the possible genotypes and their fractional representation?
For some traits, one allele is not completely dominant to another. Incomplete dominance occurs when neither allele dominates over the other. The resulting
- What type of offspring and in what ratio would you expect from a cross between a black and a white chicken?
- What type of offspring and in what ratio would you expect from a cross between a black and a grey chicken?
3. What type of offspring and in what ratio would you expect from a cross between two grey chickens?
4. Cross a pure-line red (R) snapdragon flower with a pure-line white (r) snapdragon.
- What are the possible genotypes?
5. Cross two pink snapdragons.
- What are the possible genotypes and their fractional representation?
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