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Codominance

Prompt

  1. In cattle, roan coat color is an example of an autosomal, codominant phenotype. Roan (CrCw) cattle are produced from the mating of a white (CwCw) cow to a red cow (CrCt). Predict the phenotypic and genotypic frequencies of offspring from each of the following crosses

    a. Roan x White b. Roan x Red c. Red x White d. Roan x Roan

  2. In some chickens, the gene for feather color is controlled by codominance. The allele for black is B and the allele for white is W. The heterozygous phenotype is known as erminette.

    1. What is the genotype for black chickens?
    2. What is the genotype for white chickens?
    3. What is the genotype for erminette chickens?

  3. If two erminette chickens were crossed, what is the probability that:

    1. They would have a black chick?
    2. They would have a white chick?

  4. A black chicken and a white chicken are crossed. What is the probability that they will have erminette chicks?

Response

  1. In cattle, roan coat color is an example of an autosomal, codominant phenotype. Roan (CrCw) cattle are produced from the mating of a white (CwCw) cow to a red cow (CrCr). Predict the phenotypic and genotypic frequencies of offspring from each of the following crosses:

    1. Roan (CrCw) x White (CwCw)

      • Genotypes: 50% CrCw, 50% CwCw
      • Phenotypes: 50% Roan, 50% White

    2. Roan (CrCw) x Red (CrCr)

      • Genotypes: 50% CrCw, 50% CrCr
      • Phenotypes: 50% Roan, 50% Red

    3. Red (CrCr) x White (CwCw)

      • Genotypes: 100% CrCw
      • Phenotypes: 100% Roan

    4. Roan (CrCw) x Roan (CrCw)

      • Genotypes: 25% CrCr, 50% CrCw, 25% CwCw
      • Phenotypes: 25% Red, 50% Roan, 25% White

  2. In some chickens, the gene for feather color is controlled by codominance. The allele for black is B and the allele for white is W. The heterozygous phenotype is known as erminette.

    1. Genotype for black chickens: BB
    2. Genotype for white chickens: WW
    3. Genotype for erminette chickens: BW

  3. If two erminette chickens (BW x BW) were crossed, the probabilities are:

    1. Probability of a black chick (BB): 25%
    2. Probability of a white chick (WW): 25%

  4. A black chicken (BB) and a white chicken (WW) are crossed. The probability that they will have erminette chicks (BW): 100%