Fertilisation and Embryo Cleavage

Question 1

What percentage of oocytes is chromosomally abnormal?

Answer 1

20-37%

Question 2

What percentage of sperm is chromosomally abnormal?

Answer 2

7-15%

Question 3

What percentage of zygotes is chromosomally abnormal and undergoes spontaneous abortion?

Answer 3

40%

Question 4

How long may sperm wait in the female reproductive tract?

Answer 4

5-6 days.

Question 5

At what points does meiosis pause in females?

Answer 5

At prophase I in embryogenesis, at metaphase II during puberty

Question 6

What happens during synapsis?

Answer 6

Crossing over

Question 7

What is a chiasma in terms of meiosis?

Answer 7

Areas where homologous chromosomes are locked together during recombination.

Question 8

How many diploid combinations are possible?

Answer 8

64 trillion

Question 9

What is turner syndrome?

Answer 9

X

Question 10

What is Kleinfelter syndrome?

Answer 10

XXY

Question 11

What trisomies can humans survive?

Answer 11

21, 18 and 13 (18 and 13 die soon after birth)

Question 12

For how many days are sperm motile after insemination?

Answer 12

7 days

Question 13

Where do sperm acquire some motility?

Answer 13

Epididymis

Question 14

When do sperm acquire full motility?

Answer 14

In the female reproductive tract due to uterine secretions

Question 15

What is capacitation?

Answer 15

Hyperactivity of sperm and alteration of the plasma membrane to better bind to the egg.

Question 16

How does the uterine wall induce capacitation?

Answer 16

Ca2+ influx

Question 17

What is the acrosome derived from?

Answer 17

Golgi apparatus

Question 18

What digestive enzymes does the acrosome contain?

Answer 18

hyaluronidase and acrosin

Question 19

What is the function of hyaluronidase and acrosin?

Answer 19

Break down cumulus cells.

Question 20

What is the fast block?

Answer 20

Large Na+ influx, leading to depolarisation- transient

Question 21

What is the slow block/ cortical reaction?

Answer 21

Release of Ca2+ into the egg
Stimulation of cortical granule release, which fuse under the egg surface
Cortical granule contents released into the zona pellucida (b/w cell membrane and vitelline envelope)- permanent.

Question 22

What is the function of the sperm’s centriole?

Answer 22

First cleavage.

Question 23

List the steps that follow fertilisation.

Answer 23

Egg complete meiosis II
Second polar body formed
Mitosis of zygote

Question 24

What are blastomeres?

Answer 24

Cells formed after the first division.

Question 25

How many blastomeres are there after day 1?

Answer 25

2

Question 26

How many blastomeres are there after day 2?

Answer 26

4

Question 27

What is the asymmetric hypothesis?

Answer 27

Individual blastomeres are not equivalent.

Question 28

How many blastomeres are there after days 3 and 4?

Answer 28

8

Question 29

What is the morula?

Answer 29

8 blastomere stage

Question 30

At the morula stage, does the embryo increase in size?

Answer 30

No, compaction and cleavage occurs without increase in overall size.

Question 31

Can cells be removed from the morula?

Answer 31

Yes

Question 32

What is the blastocyst and when is it formed?

Answer 32

Day 5 embryo showing cavitation (inner and outer cell masses).

Question 33

What do the peripheral blastomeres of the blastocyst form?

Answer 33

The trophoblast/trophectoderm cells to contribute to extra-embryonic tissues (placenta)