Exam 4 - Sex Determination Flashcards
Contrast vertebrate and invertebrate sex determination?
vertebrates are sexually dimorphic, this means that they are clearly either male or female.
invertebrates are less obvious and are often hermaphrodites
What two broad categories cause embryos to differentiate as a male or female?
- environmental factors
2. inherited genes
What types of environmental factors affect sex determination?
- temperature
- nutrition
- bacterial infection
- population density
At what point during development does the Y chromosome and therefore sex determination kick in in humans?
At 6 weeks
The default sex development for humans is…
female
In female development the __________________ degenerate and the ___________________ fuse part-way.
mesonephric ducts, Mullerian ducts
What does the part-way fusing of the Mullerian ducts produce in female development?
It produces the oviducts and the uterus
Which 2 Y chromosome genes expressed that are key to male development?
TDF (testis-determining factor) and SRY (sex-determining region of the Y chromosome
In male development, the _________________ deteriorate and the _________________ become the ______________
Mullerian ducts, mesonephric ducts, vans deferens
Ovaries and testis can also be referred to as?
gonads
How many types of cells make up the gonads?
at least 2 different types
What type of cell becomes the body of a gonad?
Intermediate mesoderm cells in the region of the mesonephros
What type of cells are the ones that make up the body of the gonads?
They are somatic (permanent) cells
Where do primordial germ cells come from in humans? How they get to the gonads
From the umbilical vesicle, they migrate via the gut tube. They start as a few dozen but migrate as the travel and reach the gonad as around 3,000 cells
Where do primordial germ cells come from in primates?
From the amnion
The somatic cells in the gonads proliferate to arrange themselves into rows called?
primitive sex cords
What happens to the primitive sex cords in male embryonic development?
They disappear on the edges of the gonad leaving them only in the middle or medulla of the gonad
What are the primary germ cells in male embryos called?
spermatogonia
What do the steroidal cells of male embryonic development produce? What effects does this have?
Testosterone, it produces sex characteristics (facial hair, build, etc)
What is the name of the supporting cells in male embryonic development? What critical role do they play in development?
Sertoli cells, they secrete anti-Mullerian duct hormone which leads to the deterioration of the Mullerian ducts.
Where do testis originally develop?
In the abdominal cavity, but will normally descend within one year of birth
What is the tunica albuginea?
It is a thick capsule surrounding the testis
What do the primitive sex cords eventually become in male embryonic development?
They become the seminiferous tubules
What happens to the primitive sex cords in female embryonic development?
They disappear in the middle of the gonad (leaving behind connective tissue), the ones left on the edges (cortex) will break up into primordial follicles
What are the primordial germ cells in female embryo development called?
oogonia
At what point to oogonia begin to undergo mieosis, why is this significant?
Before the 12th week of development, this leads to a female producing nearly all of the oogonia that she will have in her lifetime before birth.
What hormone do the steroidal cells in female embryo development produce?
Estrogen
What are the supporting cells in female development called?
granulosa or follicle cells
Where do ovaries originally develop?
In the abdominal cavity, and later descend into the superior end of the pelvic cavity
What could be the result of a mutated TDF gene, enhancer, or promoter?
an XY female
What 3 things determine sex?
- genetics
- embryology
- choice
What is the name of the process for dealing with the extra X chromosome that females contain?
Dosage compensation
When does dosage compensation occur?
Normally, one of the X chr. in each cell of the epiblast (about 100 cells at this point) of a female embryo is inactivated
How many genes are on the X chromosome?
1606
Is X inactivation random?
From what we have been able to study it seems so
How does X inactivation occur?
- XIST gene (found on X chromosome) is expressed
- RNA begins to coat chromosome
- As a result methylation enzymes are attracted (heavy methylation = inactivation
- The first of the 2 X chromosomes to become coated is the one that gets inactivated
What is a Barr body?
The chromosome that gets inactivated remains folded up most of the time and is visible in the nucleus as a dark spot, termed a Barr body
When is a Barr body not folded?
It unfolds only long enough to be replicated prior to mitosis
What important occurrence is the result of random X chromosome inactivation?
The rise of chimeric X-linked traits
Give 4 examples of chimeric X-linked traits?
- mouse coat color
- cat fur - calico cats
- glucose 6-phosphateD in humans
- colorblindness in humans
