Sex Determination & Development Flashcards
In female mammals, One of the X’s is ______ and appears as the barr body in the somatic cells
inactivated
What is an example of X-inactivation?
tortoise shell cat - each somatic cell expresses only 1 gene from
each pair on the X, but it is not the same gene in
every cell [mosaic]
What is virilization?
the biological development of sex differences, changes that
make a male body different from a female body. Most of the changes of virilization are produced by androgens
the development of exaggerated masculine characteristics,
usually in women, often as a result of the adrenal glands
overproducing ______
androgens
Sexual dimorphism
distinct difference in size or appearance between the sexes of an animal in addition to difference between the sexual organs
themselves.
What is an example of virilization in women?
Congenital adrenal hyperplasia
In congenital adrenal hyperplasia…
ACTH stimulates adrenal to produce cortisol but lack of enzyme for conversion of progesterone to cortisol, resulting in high concentrations of testosterone causing masculinization
A hermaphrodite is…
a Congenital malformation in sexual development; in which the
individual possesses both ovarian and testicular tissue
* Typically, one or both gonads contain both types of tissue
* Similar to mixed gonadal dysgenesis (XO;XY)
Causes of hermaphrodite, or ovotesticular syndrome-and
intersex condition
Ovum divides, each is fertilized and then they fuse early in
development (XX-XY mosaic)
– Polyspermy followed by trisomic rescue (loss of a chromosome)
– Two ova separately fertilized by 2 sperm, fuse and form a
tetragametic chimera (one male/one female)
– Mutation of the SRY gene
A male pseudohermaphrodite (XY) can be characterized as…
The individual’s matches the chromosome to gonadal tissue, but
mismatching genitalia
* For males: testis usually not descended
male pseudohermaphrodites (XY) are typically associated with…
5-a-reductase deficiency or androgen insensitivity syndrome (testicular feminization)
Androgen Insensitivity Syndrome (AIS), which is associated with male pseudohermaphrodites, has three types:
Complete (typical female external genitalia)
Mild (external genitalia are of a typical male)
Partial (external genitalia are partially masculinized)
A female pseudohermaphrodite (XX) can be characterized as…
possess ovaries but have male genitalia; usually caused by
congenital adrenal hypoplasia
In a cattle _______, the following happens: ______
This is an example of female pseudohermaphrodites.
freemartin; Twins: male and female
– a common blood supply is
established by D39
– Androgens are passed by
the fusion to the female
fetus
– Androgens stimulate
development of the male
reproductive tract
Characteristics of XXY Syndrome = Klinefelter’s Syndrome
Sterile - Testicular Hyperplasia
(extra X chromosome is retained because of a nondisjunction event)
Characteristics of XO = Turner’s Syndrome
monosomy X, no ‘Y’ chromosome
occurs in 1 out of every 2500 female births
~ 98% of all fetuses with Turner syndrome spontaneously abort
Sterile - Inactive Ovaries due to a nondisjunction event
Characteristics of Swyer Syndrome
“pure gonadal dysgenesis” (PGD)
- a 46 XY karyotype and female external genitalia
- no functional gonads are present to induce puberty in an otherwise normal girl whose karyotype is found to be XY
- gonads are found to be nonfunctional streaks - a normal vagina and uterus
Characteristics of Leydig cell hypoplasia
unlike AIS, the androgen receptor is functional
- male pseudohermaphroditism resulting from inadequate fetal testicular Leydig cell differentiation
- wide phenotypic spectrum ranging from complete female external genitalia to males with micropenis
- Enzymatic Defects in Testosterone Biosynthesis
Androgen insensitivity syndrome (AIS) results in a feminine appearance of males. In general, this is caused by the lack of androgen receptor. Can you list and discuss how androgen receptors maybe absent? Would it be possible to have androgen receptors and still have the AIS phenotype?
TBD
Development of the Gonads, Reproductive Tract and External Phenotype has three renal systems that have formed in order:
Pronephros, mesonephros, and metanephros
