Meiosis, Fertiliasation, and Infertility Flashcards
(23 cards)
What’s meiosis
Separation of homologous chromosomes
Then seperate in of sister chromatids
(From producing haploid gametes to then introducing genetic diversity via crossing over and assortment )
How many chromosomes in a human diploid somatic cell?
23 pairs of Chromosomes (22 autosomal pairs and 1 sexual pair)
46 in total (23 maternal and 23 paternal)
How many cross overs happen between each pair of human chromatids per meiosis cycle?
2-3 crossovers on average
Meiosis is regulated differently in males and females, how?
In spermatogenosis, sperm lands when you hit puberty and one parent cell produces 4 sperm cells
Oogenesis only one oocyte formed from a parent cell and other three degenerate and this starts as soon as you’re born maturation continues after puberty
What is aneuploidy?
And what happens when autosomal chromosomes go wrong?
Failure in chromosome separation in Meiosis
Down syndrome
Oocytes and sperm have different error rates in meiosis, what are some of them?
20% of oocytes are aneuploid compared to 3-4% of sperm
This 25% human foetus are aneuploid
But due to loads of mitotic divisions genetic mutations more likely before mature sperm forms
Sperm capacitation facts
-Soern cannot fertilise oocytes when newly ejaculated
-Process of capacitation takes 5-7 hours
-Capacitated sperms are more active
-capacitation occurs at the uterus and oviducts and facilitated by female substances
What is the aim of capacitation?
To increase motility of the sperm flagellum and allow sperm to undergo the acrosome reaction
-By changes in glycoproteins lipids and ion channels in PM
-Lowering resting potential
-uncover surface receptors to bind to egg (the zona pellucida)
What is the acrosome reaction?
Basically where sperm binds to zona pellicuda and releases acrosomal vesicle to get into egg cytoplasm
NB- when one sperm enters egg cortical granule release enzyme altering zona structure and not allowing anymore sperm
Fertilization summarised:
1.The plasma membranes of oocyte and sperm fuse and sperm head enters only
2.second meiotic division is complete
3.secondary oocyte arrested in metaphase and forms mature ovum
Formation of M and F pronuclei: sperm chromosome decondense the after meiosis chromosome of ovum decondense
Last step of fertilisation
Membrane of pronuclei break down and chromosomes condense and prepare for mitosis
-on membrane dissolution, there is 1 cell with 46 chromosomes= diploid/zygote
Fertilisation facts:
Completed within 24 hours of ovulation
Approx 300 million sperm when you nut in her
48 hours life span in pussy
Only 100 sperm reach fertilisation spot and most are degenerate and absorbed by genital tract
How common is having twins in the UK
1 in 80 pregnancies are twins
What is monozygotic twins
Fertilised single egg splits into two zygotes and makes them identical anis anas
1 in 250 pregnancies
Dyzygotic
Two sperm at two seperate ova reaching maturation at the same time and due to lack of ovary dominance during cycle
Not identical Wes and Owen da it can be different sex too and more likely in older women
How dna fertilisation go awry
Too many sperm leads to spontaneous abortion
Infertility
Bad timing 48 hours sperm lifespan and 24 hours after ovulated egg may not work
Who can access the ART treatment?
Couples who have been trying to get pregnant for over a year
1 in 6 couples are subfertile
25% chance only to get pregnant
IVF cycles are also 25% chance
Different causes of infertility within women?
Hormone levels, damaged ovaries, premature menopause (these are usually affecting ovulation)
Secondary amenohorrhea (pregnancy/menopause)
Fallopian tube blockage
Causes of infertility within men
Low sperm count low sperm motility and impotence (ED)
Aspermia (no sperm on ejaculation)
Environmental factors, lifestyle, age,STIs
What is ART?
Assistive reproductive technology
Intrauterine insemination or in vitro fertilisation (embryo transfer, ICSI,GIFT)
ICSI is intracytoplasmic sperm injection
GIFT is gamete intrafallopian transfer
IVF vs ICSI differences
IVF basically sperm and egg put together
ICSI you inject sperm into egg in case low motility or number
IUI aka intrauterine insemination is…
Concentrated semen put into uterus during controlled ovulation and hormonal cycle
11.4% birth per cycle
Some rules for donation of gametes
Donor remains legal parent until embryo transferred
Donor has a right to request info on birth of baby
At 16 kids have right to request non identifiying info on donor and 18 they can request full access
