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: -A heterozygous calf has one red allele and one black allele (Bb). These animals are always black. This tells you that the black allele is dominant and the red allele is recessive because the black coloration is hiding the red. We use “B” to indicate the dominant black allele and “b” for the recessive red allele.

Detailed explanation-3: -Therefore, if a female has blue eyes they can be represented by “bb” and if a male has brown eyes this can be represented as “BB” or “Bb”. The reason why brown eyes can be represented as “Bb” is that the capital “B” is dominant over the lowercase “b”.

Detailed explanation-4: -Genotypes with two alleles that are the same, i.e. ‘BB’ and ‘bb’, are known as homozygous genotypes and genotypes with two different alleles are known as heterozygous genotypes.

Detailed explanation-5: -Dominant refers to the relationship between two versions of a gene. Individuals receive two versions of each gene, known as alleles, from each parent. If the alleles of a gene are different, one allele will be expressed; it is the dominant gene. The effect of the other allele, called recessive, is masked.