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Multiple Choice
Two brown-eyed parents have a blue-eyed child. How is this possible?
A
The child's eye color is influenced by environmental factors.
B
Both parents carry a recessive allele for blue eyes.
C
Blue eyes are a dominant trait that can appear unexpectedly.
D
The child has a mutation that caused blue eyes.
Verified step by step guidance
1
Understand that eye color is a polygenic trait, primarily influenced by multiple genes, with the OCA2 and HERC2 genes playing significant roles.
Recognize that brown eyes are typically a dominant trait, while blue eyes are recessive. This means that for a child to have blue eyes, they must inherit two recessive alleles, one from each parent.
Consider the genetic makeup of the parents. If both parents have brown eyes but carry a recessive allele for blue eyes, they can be heterozygous (Bb), where 'B' represents the dominant brown allele and 'b' represents the recessive blue allele.
Use a Punnett square to visualize the genetic combinations. Each parent can pass on either the dominant 'B' allele or the recessive 'b' allele. The possible combinations for their child are BB, Bb, Bb, and bb.
Identify that the 'bb' combination results in blue eyes, which explains how two brown-eyed parents can have a blue-eyed child if both are carriers of the recessive allele.