CGC Medical Genetics & Genomic Knowledge 5

Question 1

What is the most common biological explanation for a false-positive cell-free DNA screen for a trisomy?

Accepted Answer

Confined placental mosaicism

Answer

Maternal age over 40

Answer

Multiple gestation always

Answer

Balanced translocation in fetus

Question 2

A compound heterozygote is an individual who has:

Accepted Answer

Two different pathogenic alleles at the same locus

Answer

Two identical pathogenic alleles at the same locus

Answer

One pathogenic allele at each of two different loci

Answer

A pathogenic allele and a somatic mosaic variant at different loci

Question 3

How is a variant reported when available evidence is insufficient to classify it as pathogenic or benign?

Accepted Answer

Variant of uncertain significance

Answer

Likely benign

Answer

Pathogenic

Answer

Polymorphism

Question 4

Approximately what proportion of neurofibromatosis type 1 cases arise from de novo mutations?

Accepted Answer

50%

Answer

5%

Answer

25%

Answer

90%

Question 5

What is the approximate lifetime risk of ovarian cancer for women with a BRCA1 pathogenic variant?

Accepted Answer

39-44%

Answer

10-15%

Answer

70-80%

Answer

Under 5%

Question 6

Huntington disease shows full penetrance when the CAG repeat count in HTT is at least:

Accepted Answer

40

Answer

20

Answer

27

Answer

36

Question 7

How does DNA methylation at CpG islands in a gene promoter typically affect gene expression?

Accepted Answer

It represses transcription

Answer

It enhances transcription

Answer

It causes frameshift mutations

Answer

It has no effect on expression

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