AP BIOLOGY

Detailed explanation-1: -An organism with two dominant alleles for a trait is said to have a homozygous dominant genotype. Using the eye color example, this genotype is written BB. An organism with one dominant allele and one recessive allele is said to have a heterozygous genotype. In our example, this genotype is written Bb.

Detailed explanation-2: -So, the correct answer is ‘TtRr’.

Detailed explanation-3: -A simple cross between two pure species using two gene pairs is known as a dihybrid cross. The gametes produced by a cross between a homozygous dominant round yellow plant (RRYY) and a homozygous recessive wrinkled green plant (RRYY) will be RY and RY.

Detailed explanation-4: -If the brown male had been BB, then all offspring would have been Bb and all brown. However, if the male is Bb as above and you perform a testcross, 50% of all offspring should have the bb genotype and a white phenotype.

Detailed explanation-5: -A phenomenon in which two organisms with two pairs of traits or contrasting characters are crossed is called a dihybrid cross. In the genotype TtRr, T and R are gametes for dominant traits and t and r are gametes for recessive traits. So it is a true dihybrid condition.