fertilisation

Question 1

four stages of fertilisation

Answer 1

1. sperm capacitation
2. sperm activation & interaction w oocyte
3. activation of oocyte
4. syngamy

Question 2

sperm capacitation

Answer 2

• strip glycoproteins so less stable
• Ca2+ influx > PKA phosphorylate Tyr > less stable > fuse with oocyte

Question 3

examples of sperm acrosomal contents

Answer 3

• hyaluronidase, required to digest matrix between cumulus cells to expose ZP
• acrosin, enzyme that digests ZP

Question 4

deacribe sperm activation

Answer 4

• induced by binding to ZP
• acrosome swells, membrane fuses
• activation of PKC > whiplash movement

Question 5

describe sperm binding + fusion

Answer 5

• in perivitelline space, microvilli from equatorial side bind to & envelop sperm head
• involves equatorial and postacrosomal
  membranes on oocyte and sperm respectively
• sperm stops moving, membranes fuse

Question 6

molecules for sperm binding and fusion

Answer 6

Izumo1 (sperm)
Juno (oocyte)
CD9 (tetraspanin on oocyte)

Question 7

activation of oocyte

Answer 7

• increases in [Ca2+]i
• by PLC-zeta from sperm
• occurs in waves from site of sperm entry
• every 3-15 min for next 4-5h

Question 8

cortical reaction is produced by ? and involves ?

Answer 8

produced by elevated Ca
involves release into the perivitelline space of:
- ovastatin, so cleavage of ZP3/4 and ZP2
- ZP crosslinks
- Juno exocytosed off oocyte membrane

Question 9

sequence of events leading to syngamy

Answer 9

• during oocyte-sperm fusion and second polar body expulsion, cytoplasmic sperm contents > oocyte cytoplasm
• sperm nuclear breaks down, protamines replaced with histones, chromatin unwinds. induced by oocyte factors
• paternal and maternal pronuclei form. move from subcortical position to centre of zygote. then DNA synthesis occurs to prep for first mitotic division
• membranes break down, mitotic spindle forms, chromosomes line up at equator
• syngamy = final phase of fertilisation; gametic chromosomes come together
• immediate first cell division

Question 10

parental contribution to offspring - structures

Answer 10

maternal: everything
paternal: centriole and pericentriolar material to make up centromere, ncRNA (proteins broken down, mitochondria don’t survive)

Question 11

why paternal mitochondria is broken down

Answer 11

• might be mutated by oxidative stress
• exposed to ROS from leucocytes in epididymus, during transit, and through sperm movements
• poor quality sperm have mutations & deletions in mtDNA

Question 12

are all mitochondrial diseases maternally-inherited

Answer 12

no, 85% aren’t because nuclear DNA encodes for genes involved in mt function

Question 13

types of chromosomal anomalies

Answer 13

1. errors of ploidy - won’t survive
2. errors of somy, e.g. trisomy 21
3. translocations
4. genetic mosaics (number of nuclei, chromosomal composition)

Question 14

causes of aneuploidy

Answer 14

• failure of polar body formation, cleavage division, or polyspermy
• problems with oocyte meiotic divisions
• events in ovaries/testes (mutagens)
• alcohol, anaesthesia
• increased maternal age
  (germ cells have less surveillance for mutations because need genetic diversity)

Question 15

parthenotes only having maternal chr are called

Answer 15

gynogenetic

Question 16

can gynogenetic parthenotes survive

Answer 16

only until first cleavage cause then no centriole

Question 17

complete hydratidiform moles - genetic makeup, cause

Answer 17

• 46XX or 46XY; all of paternal origin
• female pronucleus is lost + 2 sperm fertilise egg, or 1 sperm but duplicates

Question 18

partial hydratidiform moles - genetics

Answer 18

69XXX or 69XXY (cause 1 sperm duplicates or 2 sperm fertilise)

Question 19

example of unequal genetic contribution

Answer 19

IGF2/H19