Cleavage

Question 1

What is the trophoblast?

Answer 1

Outer layer of cells on the blastocyst that forms extraembryonic structures including placenta

Question 2

When are maternal gene products degraded?

Answer 2

by the 2 cell stage of development, by the four cell stage most transcription is through the embryonic genome

Question 3

Describe the methylation cycles.

Answer 3

Demethylation of maternal and paternal genomes occurs shortly after fertiliztion until morula.
Remethylation of ICM occurs until late blastocyst.
Methylation levels fall after primordial germ cells enter genital ridges.
Remethylation occurs later during gametogenesis and could lead to imprinting

Question 4

What is the inside out hypothesis?

Answer 4

Fate of the blastomere is determined by its position within the embryo not from intrinsic properties

Question 5

Cdx-2?

Answer 5

A gene involved in differentiation it is essenetial for differentiation of trophoblast and antagonistic towards Oct-4.

Question 6

Oct-4?

Answer 6

Required to permit cleavage to proceed to 2 cell stage

Question 7

Nanog?

Answer 7

Gene involved in differentiation. Produced by inner cells in late morula stage maintains integrity of inner cell mass along with Oct4.

Question 8

If nanog is not present what happens to the inner cells?

Answer 8

They differentiate into endoderm

Question 9

Sox2?

Answer 9

Gene involved in differentiation. First expressed in eight cell stage, works with Oct4 to control regulation of genes.

Question 10

Differentiate between angelman’s syndrome and prader-willi syndrome.

Answer 10

Angelman’s syndrome includes severe mental retardation, seizures, and ataxia from a maternal deletion on chromosome 15. PWS is a paternal deletion on chromosome 15 also but results in obesity short stature, hypogonadism, bowed upper lip and mild mental retardation.

Question 11

T or F: Imprinting is erased and reestablished with each round of gametogenesis.

Answer 11

True

Question 12

When does X inactivation take place?

Answer 12

First few weeks of development, once it is inactivated it remains inactive in all descendants of the first cell.

Question 13

How does X inactivation occur?

Answer 13

Xist located on the X chromosome produces and RNA molecule that coats the X chromosome and induces X inactivation.

Question 14

What is turner syndrome?

Answer 14

Missing a second X chromosome female

Question 15

What is Klinefelter syndrome?

Answer 15

Males who have an excess of X chromosomes

Question 16

What is regulation?

Answer 16

Refers to the ability of embryo to compensate for removal of structures OR addition in EARLY stages.