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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. Trisomy 21 (Down syndrome) most commonly results from which of the following mechanisms?

    Answer: Nondisjunction during meiosis

    Approximately 95% of Down syndrome cases result from nondisjunction (failure of chromosomes to separate) during meiosis I, most often in the mother, producing a gamete with two copies of chromosome 21.

  2. DNA methylation of CpG islands in a gene's promoter region typically results in:

    Answer: Gene silencing and decreased transcription

    Methylation of CpG islands in promoter regions recruits methyl-CpG-binding repressor proteins and blocks transcription factor binding, leading to gene silencing.

  3. During eukaryotic RNA processing, which modification is added to the 5' end of pre-mRNA?

    Answer: A 7-methylguanosine (m7G) cap

    A 7-methylguanosine cap is co-transcriptionally added to the 5' end of pre-mRNA, protecting it from exonucleolytic degradation and facilitating ribosome recognition for translation initiation.

  4. During translation, which RNA molecule carries specific amino acids to the ribosome?

    Answer: tRNA (transfer RNA)

    Transfer RNA (tRNA) molecules serve as adaptors, each carrying a specific amino acid and containing an anticodon that base-pairs with the complementary mRNA codon at the ribosome.

  5. The lac repressor protein is inactivated (prevented from binding the operator) when it binds to:

    Answer: Allolactose (a metabolite of lactose)

    Allolactose, produced from lactose by beta-galactosidase, acts as the true inducer by binding to the lac repressor and causing a conformational change that prevents operator binding.

  6. Which of the following best defines genetic drift?

    Answer: Random fluctuations in allele frequencies due to chance events, especially in small populations

    Genetic drift refers to stochastic, non-directional changes in allele frequencies caused by random sampling events, with its effects most pronounced in small populations.

  7. In recombinant DNA technology, restriction endonucleases are primarily used to:

    Answer: Cut DNA at specific palindromic recognition sequences

    Restriction endonucleases recognize specific short DNA sequences (typically 4–8 bp palindromes) and cleave the DNA at or near those sites, generating defined fragments for cloning or analysis.