Question 1

A microdeletion in which chromosomal region is a common cause of tetralogy of Fallot with pulmonary atresia or with absent pulmonary valve?&#10;A) 20p12&#10;B) 20q13&#10;C) 21q21&#10;D) 22q11&#10;E) Xq12

Accepted Answer

A microdeletion in the 22q11 chromosomal region is a common cause of tetralogy of Fallot with pulmonary atresia or with absent pulmonary valve. This genetic anomaly is associated with DiGeorge syndrome, which can present with a range of cardiac, immune, and developmental issues.

Question 2

Defects in which of the following cause female pseudohermaphroditism caused by congenital adrenal hyperplasia?&#10;A) Testis-determining factor&#10;B) SOX9&#10;C) DAX1&#10;D) Sex-determining region&#10;E) Cortisol biosynthesis

Accepted Answer

Female pseudohermaphroditism caused by congenital adrenal hyperplasia is due to defects in cortisol biosynthesis. This condition leads to an overproduction of androgens, causing masculinization of a genetic female's external genitalia.

Question 3

To which group of mothers are the majority of babies with Down syndrome born?&#10;A) Mothers with balanced translocations&#10;B) Mothers older than 35 years of age&#10;C) Mothers younger than 35 years of age&#10;D) Mothers with isochromosome 21&#10;E) Mothers with prior affected child

Accepted Answer

Although the risk of having a baby with Down syndrome increases with maternal age, the majority of babies with Down syndrome are born to mothers younger than 35 years of age simply because younger women have more babies overall.

Question 4

The Y chromosome undergoes recombination with which chromosome?&#10;A) It recombines along the length of the X chromosome&#10;B) It recombines with a specific region of the X chromosome&#10;C) It only recombines when there is a Y chromosomal duplication&#10;D) It often exhibits nonhomologous recombination with autosomes&#10;E) It does not undergo recombination

Accepted Answer

The Y chromosome recombines with the X chromosome, but this recombination is limited to the pseudoautosomal regions at the tips of each chromosome. These regions are homologous between the X and Y chromosomes, allowing for the necessary exchange of genetic material during meiosis in males.

Question 5

Which of the following is the most common meiotic error resulting in Down syndrome?&#10;A) Nondisjunction during maternal meiosis I&#10;B) Nondisjunction during maternal meiosis II&#10;C) Nondisjunction during paternal meiosis I&#10;D) Nondisjunction during paternal meiosis II&#10;E) These are equally likely possibilities

Accepted Answer

Nondisjunction during maternal meiosis I is the most common meiotic error leading to Down syndrome. This error results in an egg with an extra copy of chromosome 21, which, when fertilized, leads to a zygote with three copies of chromosome 21, causing Down syndrome.

Question 6

What is the mechanism by which recurrent deletions associated with contiguous gene syndromes occur?&#10;A) Restriction enzymes delete sequence at particular sites&#10;B) Aberrant recombination occurs between low copy repeats&#10;C) Deletions are flanked by fragile sites on the chromosome&#10;D) Recombination occurs with a nonhomologous chromosome&#10;E) Excision of ancient retroviral elements occurs

Accepted Answer

Aberrant recombination between low copy repeats (LCRs) is a common mechanism by which deletions (and duplications) occur, leading to contiguous gene syndromes. These LCRs can misalign during meiosis, resulting in unequal crossing over and the deletion (or duplication) of the genomic material between them.

Question 7

In females with a 47, XXX karyotype, how many of the X chromosomes are active?&#10;A) 1&#10;B) 2&#10;C) 3&#10;D) This is not a viable karyotype&#10;E) This varies on a case-by-case basis

Accepted Answer

In females with a 47, XXX karyotype, only one X chromosome is active. The other two X chromosomes undergo a process called X-inactivation, where they are largely silenced to prevent an overdose of X-linked gene expression.

Question 8

Which of the following terms is used to describe a syndrome with a phenotype that is caused by deletion of multiple, neighboring genes?&#10;A) Multifactorial disorders&#10;B) Haploinsufficiency syndrome&#10;C) Multifactored deficiency syndrome&#10;D) Contiguous gene syndrome&#10;E) Monosomy

Accepted Answer

Contiguous gene syndrome refers to a condition caused by the deletion of several neighboring genes on a chromosome, leading to a complex phenotype that involves multiple organ systems or multiple aspects of development.

Question 9

What are the three trisomies for complete autosomes that are well-defined and compatible with postnatal survival?&#10;A) Trisomy 12, 13, 21&#10;B) Trisomy 13, 15, 18&#10;C) Trisomy 11, 13, 18&#10;D) Trisomy 13, 15, 21&#10;E) Trisomy 13, 18, 21

Accepted Answer

The three trisomies for complete autosomes that are well-defined and compatible with postnatal survival are Trisomy 13 (Patau syndrome), Trisomy 18 (Edwards syndrome), and Trisomy 21 (Down syndrome).

Question 10

Which sex chromosome abnormality is associated with an increased risk of breast cancer and infertility?&#10;A) Turner syndrome&#10;B) Klinefelter syndrome&#10;C) 47, XYY&#10;D) Trisomy X&#10;E) Tetrasomy X

Accepted Answer

Klinefelter syndrome, which is characterized by a male having an extra X chromosome (47,XXY), is associated with an increased risk of breast cancer and can also lead to infertility due to hypogonadism and reduced testosterone levels.

Deck 6: The Chromosomal and Genomic Basis of Disease: Disorders of the Autosomes and Sex Chromosomes