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Genetics Flashcards

7 cards from real MCAT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. In a dihybrid cross between two heterozygous parents (AaBb × AaBb), what is the expected phenotypic ratio in the offspring?

    Answer: 9:3:3:1

    A dihybrid cross between two double heterozygotes yields a 9:3:3:1 phenotypic ratio when the genes assort independently, producing four distinct phenotypic classes.

  2. According to Hardy-Weinberg equilibrium, which condition must be met for a population to remain in equilibrium?

    Answer: Allele and genotype frequencies remain constant across generations

    Hardy-Weinberg equilibrium describes a state where allele and genotype frequencies remain constant generation after generation in the absence of evolutionary forces.

  3. During DNA replication, which enzyme synthesizes new DNA strands in the 5' to 3' direction by adding nucleotides to the growing chain?

    Answer: DNA polymerase III

    DNA polymerase III is the primary replicative polymerase in prokaryotes, extending the new strand by adding deoxyribonucleotides to the 3'-OH end in the 5' to 3' direction.

  4. A missense mutation results in which of the following outcomes?

    Answer: A different amino acid incorporated into the protein

    A missense mutation changes a single nucleotide, altering the codon so that a different amino acid is incorporated at that position in the polypeptide chain.

  5. In E. coli, when glucose is absent and lactose is present, which statement best describes the state of the lac operon?

    Answer: The operon is transcribed at high levels due to both positive and negative regulation

    With glucose absent, cAMP levels rise and activate CAP to stimulate transcription; with lactose present, allolactose inactivates the repressor, resulting in high-level transcription of the lac operon.

  6. Two genes are said to be genetically linked when they are:

    Answer: Located on the same chromosome

    Linked genes reside on the same chromosome and tend to be inherited together unless separated by crossing over during meiosis.

  7. Which of the following correctly describes the central dogma of molecular biology?

    Answer: DNA → RNA → Protein

    The central dogma describes the flow of genetic information: DNA is transcribed into RNA, which is then translated into protein.