AP BIOLOGY

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HEREDITY

MONOHYBRID CROSS

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
In rats, black coat color is dominant over white coat color. If some of the offspring of a cross between a black rat and a white rat are white, the black rat must have been-
A
homozygous dominant
B
heterozygous
C
homozygous recessive
Explanation: 

Detailed explanation-1: -Explanation: Codominance means that more than one type of dominant allele for the same gene is present. If both black and white fur are dominant, then heterozygous (Aa) offspring would be spotted with black and white.

Detailed explanation-2: -A cross of two F1 hybrids, heterozygous for a single trait that displays incomplete dominance is predicted to give a 1:2:1 ratio among both the genotypes and phenotypes of the offspring.

Detailed explanation-3: -Only offspring with the bb genotype will have the white-flower phenotype. Therefore, in this cross, you would expect three out of four (75 percent) of the offspring to have purple flowers and one out of four (25 percent) to have white flowers. These are the same percentages that Mendel got in his first experiment.

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