While lecturing on inheritance patterns, a student asks, "My mother has blue eyes and my father has brown eyes. All my siblings have brown eyes except me. How can this happen?" Which of the following is the most accurate response?
A) Phenotypically, the brown-eyed persons are the same, but genotypically they are different.
B) This is known as penetrance, where a gene has its ability to express its function.
C) Expressivity is when a gene is expressed in the phenotype.
D) Blue sclera is a genetic mutation.
Ans: A
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More than one genotype may have the same phenotype. Some brown-eyed persons carry one copy of the gene that codes for blue eyes, and other brown-eyed persons do not. Phenotypically, these two types of brown-eyed persons are the same, but genotypically they are different. Expressivity refers to the manner in which the gene is expressed in the phenotype, which can range from mild to severe. Penetrance represents the ability of a gene to express its function. Seventy-five percent penetrance means 75% of persons of a particular genotype present with a recognizable phenotype. Blue sclera is a genetic mutation but not relative in this example.
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