Oogenesis

How? Occurs by meiosis but with modifications

Female issues No point to females making millions of ova (like males make sperm) they can’t carry millions of fetuses in the womb at once. The ova survive for 72 hours. Once fertilised they provide nutrients for the growing ball of cells (blastocyst), until it implants in the uterus.

Pre-birth Germ cells undergo mitosis to multiply then the germ cells begin meiosis but stop before the first meiotic division (PRIMARY OOCYTES) Primary oocyte surrounded by follicular cells are called the PRIMARY FOLLICLE

Development - Ovulation Primary follicles are signaled by hormones during the monthly cycle one single primary oocyte completes the first meiotic division, and then ovulation occurs. An ovulated egg is called a secondary oocyte, a polar body will also be made which will result in nothing and will be reabsorbed.

Where to? The secondary oocyte travels down the fallopian tube If no sperm are encountered and fertilisation doesn’t take place the secondary oocyte will not undergo the second meiotic division.

Fertilisation The sperm break through the egg cell and this starts meiosis II where the double stranded chromosomes in the eggs nucleus have their chromatids separated and a second polar body is cast out of the division. The nucleus begins to swell and the sperm and egg nuclei approach each other

Welcome to motherhood The newly combined DNA in the zygote replicates and form chromosomes, and a mitotic division takes place

Animations / Videos Animation of the process of oogenesis http://wps.aw.com/bc_martini_eap_4/40/10469/2680298.cw/content/index.html Go to size difference between egg and sperm: http://distane.stcc.edu/aandp/ap/AP2pages/reprod/oogenesi.htm