Oogenesis n Occurs How by meiosis but with

Oogenesis

n Occurs How? by meiosis but with modifications

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

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

Development - Ovulation n Primary follicles are signaled by hormones during the monthly cycle one single primary oocyte completes the first meiotic division, and then ovulation occurs. n 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? n The secondary oocyte travels down the fallopian tube n If no sperm are encountered and fertilisation doesn’t take place the secondary oocyte will not undergo the second meiotic division.

Fertilisation n 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. n The nucleus begins to swell and the sperm and egg nuclei approach each other

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

Animations / Videos n Animation of the process of oogenesis http: //wps. aw. com/bc_martini_eap_4/40/10 469/2680298. cw/content/index. html n Go to size difference between egg and sperm: http: //distane. stcc. edu/aandp/ap/AP 2 page s/reprod/oogenesi. htm