BIOL1008 Lecture 15: Sex and Reproduction- Lecture 7- Fertilisation and Pregnancy
Fertilisation and Pregnancy
Capacitation
Tail becomes hyperactivated- beats frequently
Sperm surface membrane properties change
Facilitates acrosome reaction when meets the egg
oTriggered by Zona pellucida
oAllows sperm to bind to oocyte
Fusion of sperm and oocyte occurs in upper part of Fallopian tube (oviduct)
Fertilisation
Penetration of the oocyte by sperm triggers
completion of meiosis II, the fusion of nuclei
into a new diploid zygote, and ultimately the
cell division that produces the blastocyst
Penetration by one sperm stimulates the
granules in the egg cortex to release
substances that prevent other sperm from
entering
Fusion of sperm and egg
Cell migrates down oviduct and starts cell
division
Around 4 days to uterus
16-32 days called morula
Morula blastocyst
Seizing control
The conceptus must seize control of maternal
reproduction changing the mother’s pattern from
cyclic ovulation to pregnant
Conceptus transferred to uterus
Physical and nutritional contact made with endometrium
Conceptus interferes with pituitary-ovary interaction:
oHuman chorionic gonadotropin (HCG) binds to LH receptors in corpus luteum
oProlongs luteal phase (progesterone greater than oestrogen)
oHCG detected in urine-based pregnancy kits (12-14 days after conception)
Within 2-3 weeks the conceptus starts to synthesis steroid hormones
HCG is now unnecessary
oHuman placental lactogen (from placental tissue)
Stimulates production of prolactin from maternal pituitary
Development
Placenta: complex mixture of tissues derived from the mother, the trophoblast and
the inner cell mass- connects mother and conceptus
Developmental problems
Genetic imprinting: maternal and paternal genes can compete
Teratogen can cause developmental abnormalities
Genetic Imprinting
Normal process
One copy of the gene is switches off and you are fully reliant on the other one
working
Some of the genes that are important in early development “remember” their origin,
so that only the maternal or paternal copy is expressed
Imprinted genes are silenced genes- expression is determined by the parent that
contributed them
Means that parthenogenesis is impossible in humans (because gene expression
occurs in only one allele)
Maternal and paternal genes can compete
oBeckwith-Widermann Syndrome
1:14,000
UPD chromosome 11: 2 paternal copies
Foetus grows too fast- large organs which tend to outgrow the body
Infertile
oPrader-Willi Syndrome
Document Summary
Facilitates acrosome reaction when meets the egg: triggered by zona pellucida, allows sperm to bind to oocyte. Fusion of sperm and oocyte occurs in upper part of fallopian tube (oviduct) Penetration of the oocyte by sperm triggers completion of meiosis ii, the fusion of nuclei into a new diploid zygote, and ultimately the cell division that produces the blastocyst. Penetration by one sperm stimulates the granules in the egg cortex to release substances that prevent other sperm from entering. Cell migrates down oviduct and starts cell division. The conceptus must seize control of maternal reproduction changing the mother"s pattern from cyclic ovulation to pregnant. Conceptus interferes with pituitary-ovary interaction: human chorionic gonadotropin (hcg) binds to lh receptors in corpus luteum, prolongs luteal phase (progesterone greater than oestrogen, hcg detected in urine-based pregnancy kits (12-14 days after conception) Within 2-3 weeks the conceptus starts to synthesis steroid hormones. Hcg is now unnecessary: human placental lactogen (from placental tissue)
