Fertilisation and Embryo Cleavage Flashcards
What percentage of oocytes is chromosomally abnormal?
20-37%
What percentage of sperm is chromosomally abnormal?
7-15%
What percentage of zygotes is chromosomally abnormal and undergoes spontaneous abortion?
40%
How long may sperm wait in the female reproductive tract?
5-6 days.
At what points does meiosis pause in females?
At prophase I in embryogenesis, at metaphase II during puberty
What happens during synapsis?
Crossing over
What is a chiasma in terms of meiosis?
Areas where homologous chromosomes are locked together during recombination.
How many diploid combinations are possible?
64 trillion
What is turner syndrome?
X
What is Kleinfelter syndrome?
XXY
What trisomies can humans survive?
21, 18 and 13 (18 and 13 die soon after birth)
For how many days are sperm motile after insemination?
7 days
Where do sperm acquire some motility?
Epididymis
When do sperm acquire full motility?
In the female reproductive tract due to uterine secretions
What is capacitation?
Hyperactivity of sperm and alteration of the plasma membrane to better bind to the egg.
How does the uterine wall induce capacitation?
Ca2+ influx
What is the acrosome derived from?
Golgi apparatus
What digestive enzymes does the acrosome contain?
hyaluronidase and acrosin
What is the function of hyaluronidase and acrosin?
Break down cumulus cells.
What is the fast block?
Large Na+ influx, leading to depolarisation- transient
What is the slow block/ cortical reaction?
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.
What is the function of the sperm’s centriole?
First cleavage.
List the steps that follow fertilisation.
Egg complete meiosis II
Second polar body formed
Mitosis of zygote
What are blastomeres?
Cells formed after the first division.
How many blastomeres are there after day 1?
2
How many blastomeres are there after day 2?
4
What is the asymmetric hypothesis?
Individual blastomeres are not equivalent.
How many blastomeres are there after days 3 and 4?
8
What is the morula?
8 blastomere stage
At the morula stage, does the embryo increase in size?
No, compaction and cleavage occurs without increase in overall size.
Can cells be removed from the morula?
Yes
What is the blastocyst and when is it formed?
Day 5 embryo showing cavitation (inner and outer cell masses).
What do the peripheral blastomeres of the blastocyst form?
The trophoblast/trophectoderm cells to contribute to extra-embryonic tissues (placenta)
