pregenesis

Question 1

define pregenesis

Answer 1

developmental pre-conditions (in parents) enabling (successful) reproduction

Question 2

4 steps of pregenesis

Answer 2

1. formation and migration or parental primordial germ cells
2. cortico-medullary differentiation of gonads in mother (ovaries) and in father (testes)
3. increase the number of cells by mitosis
4. gametogenesis (meiosis), maturation of gametes, fertilization

Question 3

first sight of migration and parental primordial germ cells? origin (germ layer)? time?

Answer 3

first sight: yolk sac
germ layer: ectodermal
time: 4th week (24 days) after conception

Question 4

define meiotic disjunction

Answer 4

irregular distribution of homologous chromosomes to the cell poles

or

failure of paired chromosomes to separate regularly at first anaphase

or

the distribution of unpaired homologous to the same cell pole resulting in aneuploid products of meiosis

Question 5

most common monosomy? most common trisomy before birth? after birth?

Answer 5

most common monosomy: monosomy X

most common trisomy before birth: 16

most common trisomy after birth: 21 (down syndrome), 18 and 13

Question 6

what happens during capacitation?

Answer 6

• vaginal secretions trigger bicarbonate
• lipid and glycoprotein content of sperm membrane altered
  - this increase sperm metabolism and motility
• hyaluronidase activity

Question 7

name the barriers a sperm must penetrate and describe what they are made of

Answer 7

1. corona radiata- loosely connected granulosa cells embedded in a sticky mass of hyaluronic acid
2. zona pellucida- composed of glycoproteins
3. egg plasma membrane

Question 8

what is the basis of the acrosome reaction? what happens in this reaction?

Answer 8

the reaction is sperm based

in the reaction:

• a receptor on the zona pellucida binds an adhesion molecule on sperm cell
• binding causes influx of Ca++ into sperm cell, and enzymes from acrosomal cap break down the zona pellucida
• sperm pronucleus is added to the egg cytoplasm

Question 9

what is the basis of the cortical reaction? what happens in this reaction?

Answer 9

the reaction is egg based

in the reaction:

• once first sperm has penetrated the PLASMA MEMBRANE, there is an increase in the intracellular calcium in the ovum
• CORTICAL GRANULES respond by releasing their contents into the space outside the egg
• enzymes rapidly alter the egg membrane and zona pellucida to prevent additional binding and penetration by other sperm
  - this prevents polyspermy

Question 10

is the cell haploid or diploid once fertilized?

once fertilized, what is it called?

Answer 10

diploid

now called a zygote

Question 11

what is cleavage?

Answer 11

• once a zygote is formed, the embryo undergoes a series of special mitoses called cleavage
  
  • cell division is accompanied by reduction in cell size to reduce to normal size

Question 12

what is a blastomere?

Answer 12

an individual cell during cleavage

Question 13

what is compaction?

Answer 13

outer cells flatten

• by tight junctions between adjacent outer cells
• gap junctions link inner cells

first overt sign of differentiation

• outer cells will become the placenta
• inner cells will become the fetus

morula forms

Question 14

what are 3 results of blastocyst formation?

Answer 14

• inner cell mass (ICM)
• blastocoel
• trophoblast

Question 15

at what time period (in days) after fertilization and stage of development does the embryo enter the uterus?

Answer 15

3-4 days after fertilization

blastocyst stage of development

Question 16

list the days each of these appear post fertilization

• pronuclear stage
• 2 cell
• 4 cell
• 8 cell
• morula
• blastocyst

Answer 16

• pronuclear stage: day 0
• 2 cell: day 1
• 4 cell: day 2
• 8 cell: day 3
• morula: day 4
• blastocyst: day 5

Question 17

what happens in the week of 2s?

Answer 17

the trophoblast becomes:

• cytotrophoblast
• syncytiotrophoblast

inner cell mass becomes:

• epiblast
• hypoblast

epiblast becomes: amniotic cavity
hypoblast becomes: yolk sac
- these are the 2 cavities that form

2 cells split into 2 cells (4 cells total) and 2 cavities are formed

Question 18

what is the purpose of the yolk sac and the amnion?

Answer 18

yolk sac:

• giver of life. it is a precursor to blood cells and primordial germ cells
• component of the umbilicus

amnion
- exercise and cushion room for the fetus

Question 19

what is the chorion?

Answer 19

• outermost sac of the placenta

- exchange between fetal and maternal circulation