CHAPTER 7_Sex Determination and Sex Chromosomes Flashcards
a method in which specific probes bind to specific sequences of DNA
fluorescence in situ hybridization (FISH)
males produce gametes with different chromosome compositions
heterogametic sex
the female, which has like sex chromosomes, is the __________
homogametic sex
Slight enlargement of the breasts
gynecomastia
somatic cells display two different genetic cell lines, each exhibiting a different karyotype
mosaics
cortex and medulla are the outer and inner tissues of an organ, respectively
The cortex is capable of developing into… (ovary or testes)?
Ovary
The medulla is capable of developing into… (ovary or testes)?
Testes
two sets of undifferentiated ducts called the Wolffian and Müllerian ducts exist in each embryo
Wolffian ducts differentiate into other organs of the male reproductive tract, while Müllerian ducts differentiate into structures of the female reproductive tract.
Because gonadal ridges can form either ovaries or testes, they are commonly referred to as _______
bipotential gonads
Y chromosome has at least ____ genes, compare to _____ genes on the X
75
900–1400
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.
pseudoautosomal regions (PARs)
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 ________
95%
nonrecombining region of the Y (NRY)
male-specific region of the Y (MSY)
The MSY is divided about equally between
_____________, containing functional genes, and _____________, lacking gene
euchromatic regions
heterochromatic regions
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 _________________
sex-determining region Y (SRY)
At six to eight weeks of development, the SRY gene becomes active in XY embryos
SRY encodes a protein that causes the undifferentiated gonadal tissue of the embryo to form testes This protein is called the ________
testis-determining factor (TDF)
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
XY sex reversal or Swyer syndrome
TDF functions as a ___________, a DNA-binding protein that interacts directly with regulatory sequences of other genes to stimulate their expression.
transcription factor
One potential target for activation by TDF that has been extensively studied is the gene for ___________, [also called ___________, or ___________].
Müllerian inhibiting substance (MIS
Mullerian inhibiting hormone, (MIH)
anti-Mullerian hormone
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.
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
human SOX9 gene
mouse homolog Sox9
seminiferous tubules
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.
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.
SF1
in adult female mice, deletion of a gene ______, which encodes a transcription factor, leads to transdifferentiation of the ovary into the testis
Foxl2
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
X-transposed region
Xq21
sequences of base pairs that read the same but in the opposite direction on complementary strands
palindromes
