CHAPTER 7_Sex Determination and Sex Chromosomes

Question 1

a method in which specific probes bind to specific sequences of DNA

Answer 1

fluorescence in situ hybridization (FISH)

Question 2

males produce gametes with different chromosome compositions

Answer 2

heterogametic sex

Question 3

the female, which has like sex chromosomes, is the __________

Answer 3

homogametic sex

Question 4

Slight enlargement of the breasts

Answer 4

gynecomastia

Question 5

somatic cells display two different genetic cell lines, each exhibiting a different karyotype

Answer 5

mosaics

Question 6

cortex and medulla are the outer and inner tissues of an organ, respectively

Question 7

The cortex is capable of developing into… (ovary or testes)?

Answer 7

Ovary

Question 8

The medulla is capable of developing into… (ovary or testes)?

Answer 8

Testes

Question 8

two sets of undifferentiated ducts called the Wolffian and Müllerian ducts exist in each embryo

Answer 8

Wolffian ducts differentiate into other organs of the male reproductive tract, while Müllerian ducts differentiate into structures of the female reproductive tract.

Question 9

Because gonadal ridges can form either ovaries or testes, they are commonly referred to as _______

Answer 9

bipotential gonads

Question 10

Y chromosome has at least ____ genes, compare to _____ genes on the X

Answer 10

75
900–1400

Question 11

Present on both ends of the Y chromosome are so-called ________ that share homology with regions on the X chromosome and synapse and recombine with it during meiosis.

Answer 11

pseudoautosomal regions (PARs)

Question 12

The remainder of the chromosome, about ___ percent of it, does not synapse or recombine with the X chromosome. As a result, it was originally referred to as the ________. More recently, researchers have designated this region as the ________

Answer 12

95%
nonrecombining region of the Y (NRY)
male-specific region of the Y (MSY)

Question 13

The MSY is divided about equally between
_____________, containing functional genes, and _____________, lacking gene

Answer 13

euchromatic regions
heterochromatic regions

Question 14

Within euchromatin, adjacent to the PAR of the short arm of the Y chromosome, is a critical gene that controls male sexual development, called the _________________

Answer 14

sex-determining region Y (SRY)

At six to eight weeks of development, the SRY gene becomes active in XY embryos

Question 15

SRY encodes a protein that causes the undifferentiated gonadal tissue of the embryo to form testes This protein is called the ________

Answer 15

testis-determining factor (TDF)

Question 16

there are human males who have two X and no Y chromosomes. Often, attached to one of their X chromosomes is the region of the Y that contains SRY. There are also females who have one X and one Y chromosome, a condition known as _____________. Their Y is almost always missing the SRY gene or they have a specific mutation in SRY

Answer 16

XY sex reversal or Swyer syndrome

Question 17

TDF functions as a ___________, a DNA-binding protein that interacts directly with regulatory sequences of other genes to stimulate their expression.

Answer 17

transcription factor

Question 18

One potential target for activation by TDF that has been extensively studied is the gene for ___________, [also called ___________, or ___________].

Answer 18

Müllerian inhibiting substance (MIS
Mullerian inhibiting hormone, (MIH)
anti-Mullerian hormone

Question 19

Cells of the developing testes secrete MIS. As its name suggests, MIS protein causes regression (atrophy) of cells in the Müllerian duct. Degeneration of the duct prevents formation of the female reproductive tract.

Question 20

Other autosomal genes are part of a cascade of genetic expression initiated by SRY.

Examples include the _________ and
the ________, which when activated by SRY, leads to the differentiation of cells that form the __________ that contain male germ cells

Answer 20

human SOX9 gene
mouse homolog Sox9

seminiferous tubules

Question 21

fibroblast growth factor 9 (Fgf 9) is upregulated in XY gonads. Testis development is completely blocked in gonads lacking Fgf9, and signs of ovarian development occur.

Question 22

Another gene, ___, is involved in the regulation of enzymes affecting steroid metabolism. In mice, this gene is initially active in both the male and female bisexual genital ridge, persisting until the point in development when testis formation is apparent. At that time, its expression persists in males but is extinguished in females.

Answer 22

SF1

Question 23

in adult female mice, deletion of a gene ______, which encodes a transcription factor, leads to transdifferentiation of the ovary into the testis

Answer 23

Foxl2

Question 24

The MSY consists of about 23 million base pairs (23 Mb) and can be divided into three regions.

The first region is the __________. It comprises about 15% of the MSY and was originally derived from the X chromosome in the course of human evolution (about 3 to 4 million years ago). The ————- is 99% identical to region _____ of the modern human X chromosome

Answer 24

X-transposed region
Xq21

Question 25

sequences of base pairs that read the same but in the opposite direction on complementary strands

Answer 25

palindromes