Final answer:
Two brown-eyed parents can produce a green-eyed child if both are heterozygous, carrying the allele for green eyes on the green-blue eye gene. This illustrates the complex inheritance patterns, such as polygenic inheritance and epistasis, which go beyond simple Mendelian genetics.
Step-by-step explanation:
Understanding Eye Color Inheritance in Humans
Eye color in humans is a characteristic that is determined by multiple genes, which exhibit complex inheritance patterns beyond simple Mendelian genetics. Specifically, at least eight genes are known to contribute to eye color, each with two or more alleles. In the scenario where both parents have brown eyes but produce a green-eyed child, it is genetically possible if both parents are heterozygous, carrying the allele for green eyes. The correct answer from the provided choices is (b) Both parents are heterozygous, having the green trait on the green-blue eye gene.
Mendelian genetics often refers to situations where a single gene with two alleles determines a trait, with one allele being dominant over the recessive one. However, with traits like eye color, complex patterns of inheritance such as polygenic inheritance and multiple alleles come into play. This complexity illustrates why two brown-eyed parents can have a green-eyed child if both carry the allele for green eyes, but it is not dominant in their own phenotype. The inheritance involves epistasis, where one gene can mask the expression of another gene, and linkage, which describes genes being inherited together due to their close proximity on the chromosome.