Molecular Genetics & Mechanisms of Inheritance Flashcards

Which type of mutation involves the insertion of one or two nucleotides, causing a shift in the reading frame of downstream codons?

Answer: Frameshift mutation

A frameshift mutation results from insertion or deletion of nucleotides in a number not divisible by three, altering every codon downstream of the mutation.

Which DNA repair mechanism corrects single-strand mismatches introduced during replication and is defective in Lynch syndrome?

Answer: Mismatch repair

Mismatch repair (MMR) corrects replication errors; germline mutations in MMR genes (MLH1, MSH2, MSH6, PMS2) cause Lynch syndrome.

What term describes the phenomenon where the expression of a gene depends on whether it was inherited from the mother or the father?

Answer: Genomic imprinting

Genomic imprinting is an epigenetic process by which gene expression is determined by the parental origin of the allele.

During meiosis I, homologous chromosomes exchange segments in a process called:

Answer: Crossing over (recombination)

Crossing over (recombination) occurs during prophase I of meiosis when homologous chromosomes exchange corresponding segments, generating genetic diversity.

Which of the following best describes a de novo mutation?

Answer: A mutation that arises newly in the affected individual and is not present in either parent

A de novo mutation arises spontaneously in the proband and is not inherited from either parent, often explaining isolated cases of dominant disorders.

In the context of trinucleotide repeat expansion disorders, which mechanism best explains the phenomenon of anticipation?

Answer: Repeat sequences become unstable and tend to expand further with each successive transmission

Trinucleotide repeat tracts are meiotically unstable and tend to expand during transmission, leading to progressively larger repeats and earlier/more severe disease in successive generations.

Which of the following epigenetic modifications most directly contributes to gene silencing by adding a chemical group to cytosine residues in CpG islands?

Answer: DNA methylation

DNA methylation at CpG islands, catalyzed by DNA methyltransferases, is strongly associated with transcriptional silencing of the associated gene.