Fertilization and Implantation and Week 1 post-fertilization

Question 1

What is fertilization?

Answer 1

fusion of 1 male gamete with 1 female gamete

Question 2

What are the 7 requirements for in vivo fertilization?

Answer 2

1. Successful coitus including release of semen into vagina
2. Adequate numbers of competent spermatozoa
3. Ability of spermatozoa to overcome obstacles in female genital tract
4. Ovum must encounter competent spermatozoon within 24hrs of release
5. Ovum must be free from structural and chromosomal abnormalities.
6. Female genital tract must be free from infections and appropriately primed by sex hormones.
7. Spermatozoa undergo 2 processes in the female genital tract to prepare them for fertilization

Question 3

What are the 2 processes spermatozoa go through to prepare them for fertilization?

Answer 3

1. Capacitation

2. Acrosomal reaction

Question 4

When does fertilization occur?

Answer 4

Occurs when there is a binding and fusion of the oocyte and sperm cell membranes.

Question 5

What does fertilization first result in?

Answer 5

Release of paternal chromosomes from sperm head into oocyte to form male pronucleus

Question 6

The 6 immediate events of fertilization are

Answer 6

1. Completion of 2nd meiotic division of oocyte, formation of female pronucleus and expulsion of secondary polar body.
2. Formation of zygote by fusion of male and female pronuclei
3. Determination of genetic sex of zygote
4. Restoration of diploid number of chromosomes (46)
5. Introduction of genetic variation
6. Initiation of cleavage of zygote

Question 7

What results in genetic variation in a zygote?

Answer 7

1. Crossing over

2. Independent assortment of chromosomes

Question 8

What is cleavage?

Answer 8

the successive mitotic divisions of zygote

Question 9

When does cleavage commence?

Answer 9

Commences 24hrs post-fertilization

Question 10

What are the daughter cells in cleavage called?

Answer 10

blastomeres

Question 11

What encloses blastomeres?

Answer 11

zona pelucida of precursor ovum

Question 12

Where does cleavage occur?

Answer 12

Within the oviducts

Question 13

What happens between divisions and to nuclear to cytoplasmic ratio?

Answer 13

no growths between divisions

nuclear to cytoplasmic ration decreases about 1000 fold (G1 is almost absent)

Question 14

What happens to the cell cycles during cleavage?

Answer 14

they are unusual lacking or having very short G1 and G2 phases

Question 15

Cleavage continues throughout

Answer 15

first week

Question 16

What is a morula?

Answer 16

ball of blastomeres from 16-cell stage

Question 17

During week 1 post-fertilization?

Answer 17

morula is transported from the oviduct towards the cavity of the uterus

Question 18

What happens if the zona pellucida splits during cleavage?

Answer 18

monozygotic twinning will occur

Question 19

When do blastomeres differentiate into 2 cell groups?

Answer 19

5-7 days post-fertilization

Question 20

What are trophoblasts?

Answer 20

one of the group of cells from blastomeres that form a single peripheral layer around a cavity filled with fluid.

Question 21

What happens to the remaining cells after trophoblast formation?

Answer 21

they aggregate inside the ball of cells and are known inner cell mass or embryoblasts

Question 22

What is a blastocyst?

Answer 22

the resulting structure from the grouping of blastomeres

Question 23

What’s the 1st stage of obvious cell division?

Answer 23

blastocyst formation

Question 24

What do embryoblasts give rise to?

Answer 24

embryo or foetus

Question 25

What do trophoblasts give rise to?

Answer 25

placenta, chorion and umbilical cord(major components of foetal membranes)