Kaplan Nursing Entrance Practice Exam

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Prepare for the Kaplan Nursing Entrance Exam with our comprehensive quiz. Utilize flashcards and multiple choice questions, each with detailed hints and explanations, to increase your readiness and confidence for the test!

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A recessive allele will be expressed under which condition?

When it is the only allele present
When paired with another recessive allele
When paired with a dominant allele
When it is inherited from the mother only

The correct answer is: When paired with another recessive allele

A recessive allele is expressed when it is paired with another recessive allele, which means that both inherited alleles must be recessive for the phenotype associated with that recessive trait to be observable. This is due to the nature of how alleles interact; a dominant allele can mask the effects of a recessive allele if they are present together. Thus, the phenotype corresponding to the recessive allele will not be manifested unless both alleles in the gene pair are recessive. When only one recessive allele is present alongside a dominant allele, the dominant allele will determine the phenotype, leaving the recessive allele unexpressed. Furthermore, receiving a recessive allele from just one parent is insufficient for its expression, which also rules out the idea that recessive traits can be passed down based solely on maternal inheritance or combined with dominant alleles. Thus, pairing with another recessive allele is the condition necessary for expression.