Sex Determination- Lecture 1

Question 1

Mesonephros

Answer 1

Embryonic kidneys. Serve as a excretory organ during gestation. Drained by a duct system: mesonephric ducts (wolffian ducts)

Question 2

Genital swelling

Answer 2

like the genital tubercle it will develop into a scrotum or vulva depending on the presence or absence of androgens (testosterone or DHT)

Question 2

Intersex

Answer 2

any situation where there is ambiguity in the structure of the external genitalia, internal genitalia, or gonads

Question 3

Genital tubercle

Answer 3

Is a bipotential structure. In the presence of DHT or testosterone the tubercle develops into a penis. In the absence of those hormones the tubercle develops into a clitoris.

Question 3

Gonadal dysgenesis

Answer 3

gonads fail to differentiate and remain in embryonic form, termed “streak” gonads

Question 4

Paramesonephric/ Mullerian ducts

Answer 4

Tubular system developing at same time at mesonephros. Will later form the oviducts, uterus, cervix, and cranial vagina in females, or regresses in males.

Question 5

Haploid

Answer 5

number of chromosomes in the gamete (N)

Question 7

Gonadal sex

Answer 7

Testis or Ovary Determined by presence or absence of SRY (Sex-determining region of Y chromosome) gene of Y chromosome

Question 8

Male pseudohermaphrodite

Answer 8

XY with testes but has female or ambiguous external genitalia

Question 8

Female pseudohermaphrodite

Answer 8

XX with ovaries and male or ambiguous external genitalia

Question 9

Sry

Answer 9

Sex-determining region on the Y chromosome. Produces a protein called HY antigen (Sry protein), which action is to initiate differentiation of the bipotential gonadal tissue into testicular tissue. Other genes that support Sry: Sox9, Gata4, Wtl, and Sfl

Question 10

XXX

Answer 10

Associated with female phenotype, but is abnormal. Bilateral small, inactive ovaries and a hypoplastic uterus and cervix.

Question 11

Diploid

Answer 11

number of chromosomes in somatic cells (2N)

Question 12

XXY-syndrome

Answer 12

Klinefelter’s syndrome Due to presence of Y chromosome and consequently the Sry gene the individuals are phenotypically male although abnormally so. Small, flaccid testes (or retained) and azoospermia. Patient will have normal libido and behavior but often infertile.

Question 12

XX sex-reversed male

Answer 12

can be Sry positive or negative. If positive the individual has a translocated copy of Sry, which drives gonadal differentiation in the male direction. If Sry negative, they likely have mutations in genes downstream of Sry.

Question 14

Bipotential gonads

Answer 14

Gonad is undifferentiated. Both the male and female tubular systems are present. Sex of embryo cannot yet be determined

Question 15

Differentiation of ovaries (from gonadal cords)

Answer 15

Gonadal cords break apart into small clusters to form follicles, with one or more germ cells in the center. The mesonephric duct regresses while the paramesonephric duct persists and will form oviducts, uterus, cervix, and cranial vagina.

Question 16

Mesonephric/ Wolffian ducts

Answer 16

Will later form the epididymis, seminal vesicles and ductus deferens in males, or regresses in females

Question 16

Mosaics and Chimeras

Answer 16

are animals that have than one genetically-distinct population of cells. In mosaics, the different cell types all arise from a single zygote. Results from non-disjunction during mitosis In chimeras, the different cell types originate from more than one zygote.

Question 17

Aneuploidy

Answer 17

increase or decrease in normal chromosomal number, leading to trisomy or monosomy

Question 18

Fetal leydig cells

Answer 18

Especially important. They produce testosterone, that is essential for normal development of male duct system, external genitalia, secondary sex characteristics and brain.

Question 19

Polled intersex goats

Answer 19

There is a close relationship between the gene for “polled”” (hornless) and intersexuality. The polled gene is dominant autosomal. In XX patients: PP= hornless and infertile Pp= hornless and fertile pp=horned and fertile

Question 21

Phenotypic sex

Answer 21

Male or Female determined by substances produced by testis that cause either regression/maintenance of the male/female tract. These substances also regulate the development of external genitalia, secondary sex characteristics, brain development, ect

Question 23

Trisomy

Answer 23

extra chromosome added to a homologous pair

Question 24

AMH

Answer 24

Anti-mullerian hormone; produced by the sertoli cells (only in male). Causes regression of the mullerian/paramesonephric duct system

Question 25

Monosomy (XO)

Answer 25

Turner’s syndrome. Patient will be small, infertile, hypoplastic female reproductive tracts with gonadal dysgenesis and have a lack of cyclicity. External genitalia can be normal or underdeveloped.

Question 26

Congenital adrenal hyperplasia

Answer 26

individuals are XX with ovaries, but external genitalia is male. This results from a deficiency of 21-hydroxalase, which converts progesterone to cotisol. Excess progesterone is instead converted to testosterone, which masculinizes the individual

Question 27

Differentiation of testis (from the primitive sex cords)

Answer 27

Testicular cords form and differentiate into seminiferous tubules. Germ cells line the seminiferous tubules and become spermatogonia. Mesonephric duct differentiates. Mesonephric tubules become efferent ducts and rete testis.

Question 28

Freemartins

Answer 28

When a cow is pregnant with twins (one of each sex), the offspring will be a normal bull calf and a freemartin heifer calf. The heifer is almost always infertile. The heifer was exposed to HY antigen throughout gestation. This leads to underdeveloped female internal tracts or masculinized gonads.

Question 29

DHT

Answer 29

Dihydrotestosterone. Is a hormone that is converted from testosterone by 5-alpha-reductase. It acts like testosterone, but 10 times more potent

Question 30

Hermaphrodite

Answer 30

an individual have both testicular and ovarian tissue

Question 32

X chromosome inactivation

Answer 32

In early embryogenesis in mammals, one of the two X chromosomes in each cell inactivate. It occurs randomly meaning all normal females are actually mosaics. Ex: Tortiseshell cats

Question 33

Early embryo

Answer 33

Primordial germ cells develop in the yolk sac, then migrate to the hindgut and finally the genital ridge. The cells go thru many mitotic divisions during this migration. The germ cells once arrived at genital ridge organize into cords of issue (primitive sex cords)

Question 34

Testicular feminization

Answer 34

Patients are XY with retained testes.External genitalia are either female or ambiguous in appearance. This results from a defective androgen receptor (located on maternal X chromosome). The receptor cannot bind testosterone, leading it unable to exert its effects.

Question 35

Chromosomal (genotypic) sex

Answer 35

XX or XY Determined at fertilization in mammals by the sex chromosome contributed by the sperm. Females are XX and males are XY

Question 36

Genital ridge

Answer 36

Is the precursor of the gonad. Located just medial to the mesonephros (embryonic kidneys)

Question 37

XY sex-reversed female

Answer 37

Occurs due to absent or nonfunctional Sry. Affected individuals can have completely undifferentiated gonads (steak gonads). Phenotype is female but tubular tract is underdeveloped.

Question 38

Testosterone

Answer 38

Produced by leydig cells (only in male). Causes development and maintenance of wolffian/mesonephric duct system