Question 1

Which of the following best explains why the presence of the SRY gene on the Y chromosome determines maleness in humans?

Accepted Answer

SRY encodes the testis-determining factor (TDF), which triggers the formation of testes and subsequent male differentiation.

Question 2

A geneticist observes a human karyotype with 47 chromosomes, including three copies of chromosome 21. Which condition does this individual most likely have?

Accepted Answer

Down syndrome (Trisomy 21)

Question 3

Which of the following mechanisms most commonly leads to aneuploidy in humans?

Accepted Answer

Nondisjunction during meiosis

Question 4

In reptiles such as turtles and crocodiles, what is the primary environmental factor that determines the sex of the offspring?

Accepted Answer

Temperature

Question 5

Which of the following best describes polyploidy?

Accepted Answer

The presence of one or more extra sets of chromosomes in an organism

Question 6

A patient is diagnosed with a chromosomal inversion. Which of the following best describes this type of chromosomal aberration?

Accepted Answer

A segment of a chromosome is reversed end to end with no loss of genetic material

Question 7

Which of the following is a direct consequence of nondisjunction during meiosis I?

Accepted Answer

Half of the gametes will be monosomic and half will be trisomic for a particular chromosome

Question 8

Which diagnostic technique involves obtaining fetal cells from amniotic fluid for cytogenetic analysis?

Accepted Answer

Amniocentesis

Question 9

What is the most likely outcome if a human zygote is monosomic for an autosome?

Accepted Answer

The zygote will likely result in spontaneous abortion

Question 10

Which of the following best explains the decreased risk of solid tumor cancers in individuals with Down syndrome?

Accepted Answer

The presence of an extra copy of DSCR1 gene, which encodes a protein that inhibits vascular endothelial growth factor (VEGF) signaling

Question 11

Which of the following equations correctly represents the chromosome number in a human with Down syndrome?

Accepted Answer

$$2n + 1 = 47$$

Question 12

A chromosomal aberration results in a segment of chromosome 5 being transferred to chromosome 15. What is this type of aberration called?

Accepted Answer

Translocation

Question 13

Which of the following statements about haploinsufficiency is correct?

Accepted Answer

One copy of a recessive gene is not sufficient to provide normal function for the organism

Question 14

Which of the following best describes the effect of a pericentric inversion during meiosis?

Accepted Answer

It can lead to duplications and deletions in the resultant gametes

Question 15

A woman over 40 is pregnant and wants to know her risk of having a child with Down syndrome. Which factor is most relevant to her increased risk?

Accepted Answer

Increased rate of nondisjunction in her oocytes with age

Question 16

Which of the following is a likely result of unequal crossing over during meiosis?

Accepted Answer

One chromosome has a duplication and the other has a deletion

Question 17

Which of the following is true regarding the pseudoautosomal regions (PARs) of the Y chromosome?

Accepted Answer

They are regions at the ends of the Y chromosome that share homology with the X chromosome

Question 18

Which of the following best describes the role of amniocentesis in prenatal diagnosis?

Accepted Answer

It involves culturing fetal cells obtained from amniotic fluid for cytogenetic analysis

Question 19

Which of the following statements about chromosomal deletions is correct?

Accepted Answer

Deletions involve the loss of genetic material from a chromosome

Sex Chromosomes and Chromosomal Aberrations – Study Notes

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