Genetics - Sex Determination, Abnormalities Flashcards Preview

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Flashcards in Genetics - Sex Determination, Abnormalities Deck (14)
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1

Describe gametogenesis, starting with week 4 of embryogenesis.

- Week 4: primordial germ cells originate in endoderm of the yolk sac
- Week 6: primordial germ cells migrate to the genital ridge and associate with somatic cells to form the primitive gonad
- Gonads then differentiate into ovaries (default) or testes (if SRY is present)
- Within the differentiated gonads meiosis gives rise to eggs/sperm

2

Spermatogenesis:
where, how/when

- in seminiferous tubules of the testes
- prior to puberty: primordial germ cells undergo mitosis and line the tubules
- during puberty: spermatogonia (2N) --> 1˚ spermatocytes (2N) --> 2˚ spermatocytes (N) --> spermatids (N; homologues just separate); mature into sperm via capacitation

3

Oogenesis:
where, how/when

- in ovaries
- prior to birth: oogonium --> 1˚ oocyte --> 2˚ oocyte; meiosis I arrests here
- at ovulation: meiosis I completes
- at fertilization: meiosis II completes; conversion of 2˚ oocyte to egg

4

Steps of meiosis I and II

- Interphase: DNA replication, chromosomes are at 2N
- Meiosis I: PMAT
*Prophase has several stages:
1) leptotene - chromosomes replicated
2) zygotene - pairs of chromatids pair up and synapse
3) pachytene - can see tetrad (4 chromatids)
4) diplotene - crossing over
5) diakinesis - oogenesis freezes here
- Metaphase: nuclear membrane disappears, spindles appear, pairs align on metaphase plate
- Anaphase: chromatids pulled apart by spindles
- Telophase/Cytokinesis: cell division
Meiosis II - same steps, just faster

5

During which meiosis does nondisjunction occur?

Meiosis I, when the chromosomes align on metaphase plate
*cocaine/environmental exposures during pregnancy will therefore not affect nondisjunction

6

Describe the embryogenesis of the Mullerian system.

Because there is no AMH produced (by Sertoli cells) in the female, the Mullerian ducts persist and the Wolffian ducts degenerate. Around 6-11 weeks the ducts fuse to form the fallopian tubes, uterus, cervix and upper 2/3 vagina. Reabsorption of the utero-vaginal septum occurs cranially and caudally.

7

Describe the morphology of the following Mullerian duct abnormalities (MDAs):
Didelphic
Unicornuate
Bicornuate

Didelphic = ducts fail to fuse all the way down
Unicornuate = only one duct forms
Bicornuate (partial or complete) = ridge forms at the top of the uterus where ducts failed to fuse; in complete, extends to cervix

8

Describe the anatomical and clinical significance of a Unicornuate MDA.

- 1 tube, 1 uterus, 2 ovaries, +/- rudimentary horn w/wo communication to dominant horn
- Ipsi renal abnormalities 40% pts
- Pregnancy can be normal, pre-term labor, or malpresentation (breech)

9

Describe the anatomical and clinical significance of a Uterus didelphys MDA.

- 2 tubes, 2 ovaries, 2 cervixes, 2 upper vaginas, 2 everything, lower vagina +/- septum
- Renal agenesis on one side
- Pregnancy can be normal or pre-term labor

10

Describe the anatomical and clinical significance of a Bicornuate MDA.

- has a cleft in external contour of uterine fundus
- often asx, may be partial or complete, +/- vaginal septum

11

Describe the anatomical and clinical significance of a septate uterus MDA.

- smooth external uterine surface but septated uterus, partial or complete, from failure of the septum to be reabsorbed
- most common MDA
- Pregnancy can be spontaneous loss, implantation area compromised by avascular area (ie, the fibrous septum that's still present)

12

Describe the clinical significance of a DES/T-shaped uterus MDA.

- in the 50-60s pregnant women were given diethystilbesterol (DES), a hormone believed to prevent miscarriage, but actually turned out to be a teratogen
- their female children developed uterine abnormalities including T-shaped uterus, which put them at risk for pregnancy loss, as well as increased risk of vaginal clear cell carcinoma

13

What is Rokitansky Kunster Hauser syndrome?

- complete agenesis of Mullerian structures
- presents with amenorrhea (note there are ovaries so secondary sex characteristics will occur)
- lacks upper vagina, cervix, uterus, or tubes; renal and skeletal abnormalities also present
- treatment: create a neovagina

14

What is imperforate hymen?

- failure of reabsorption of uterovaginal septum
- presents with amenorrhea, cyclic pain (seems like menstrual cramps, is moody, etc), abdominal mass
- there is also a hematoma form the non-evacuated cycles
- treatment: hymenotomy and hematoma evacuation