Final answer:
Cheryl's genotype must be bb, as she needs two recessive alleles to express blue eyes. Her father has brown eyes and must be heterozygous (Bb), as he carried a recessive blue eye allele. The situation exemplifies Mendelian inheritance where the recessive trait (blue eyes) is expressed only when an individual inherits two recessive alleles.
Step-by-step explanation:
In human genetics, eye color is a characteristic that is influenced by multiple genes. For the situation described in the question regarding Cheryl's blue eyes despite having a blue-eyed mother and a brown-eyed father, it is important to understand Mendelian inheritance. Eye color inheritance revolves primarily around two alleles: the dominant allele for brown eyes (B) and the recessive allele for blue eyes (b).
Given that Cheryl has blue eyes, we can deduce her genotype must be bb, as she would need to inherit two recessive alleles to express the blue eye color; one allele from each parent. Since Brown is dominant (B), her father must have had one dominant allele and one recessive allele to be able to pass the blue eye allele to Cheryl, indicating he is heterozygous (Bb). Thus, the correct answer is B) Cheryl's own genotype must be bb; her father must be heterozygous.
Using a Punnett square, we can visualize how two heterozygous brown-eyed parents (Bb) can produce a child with green eyes, if green is an intermediate trait or a result of multiple genes interacting, which is not fully explained by simple Mendelian inheritance.