CGC Molecular Genetics & Mechanisms of Inheritance 2

Question 1

A splicing mutation that activates a cryptic splice site would most likely result in which of the following?

Accepted Answer

An mRNA with an additional segment of intronic sequence or deletion of exonic sequence

Answer

Cryptic splice site activation causes the spliceosome to use an alternative splice site, incorporating intronic sequence into the mRNA or skipping part of an exon, altering the protein.

Question 2

Uniparental disomy (UPD) can cause disease even in the absence of a traditional mutation. Which mechanism most commonly explains pathogenicity of UPD?

Accepted Answer

Disruption of imprinted gene dosage when both copies derive from one parent

Answer

UPD causes disease primarily by disrupting imprinted loci—when both copies come from one parent, imprinted genes that should be expressed from only the maternal or paternal allele are either doubly silenced or doubly expressed.

Question 3

Loss of heterozygosity (LOH) in tumor cells most often represents which event according to Knudson's two-hit hypothesis?

Accepted Answer

Somatic inactivation of the remaining wild-type tumor suppressor allele

Answer

In hereditary cancer syndromes, the first hit is the inherited germline mutation; LOH in tumor tissue represents somatic inactivation (the second hit) of the remaining wild-type allele of the tumor suppressor gene.

Question 4

Which of the following correctly distinguishes an oncogene from a tumor suppressor gene regarding mechanism of cancer causation?

Accepted Answer

Oncogenes cause cancer by gain-of-function mutations acting dominantly; tumor suppressors cause cancer when both alleles are inactivated (recessive)

Answer

Oncogenes act dominantly—a single gain-of-function mutation drives uncontrolled cell growth—whereas tumor suppressor genes act recessively, requiring biallelic inactivation to lose growth control.

Question 5

X-inactivation (lyonization) in females results in which of the following outcomes relevant to X-linked carrier females?

Accepted Answer

Random inactivation of one X per cell that becomes fixed clonally, potentially leading to skewed X-inactivation in some tissues

Answer

X-inactivation is random per cell but fixed clonally; extreme skewing toward inactivating the normal X can cause manifesting carrier females to express X-linked recessive conditions.

CGC - Certified Genetic Counselor Practice Test

CGC - Certified Genetic Counselor Practice Test

CGC Molecular Genetics & Mechanisms of Inheritance 2