gamete devloment

Gamete Development

Differs in Males and Females

Spermatogenesis

Spermatogenesis is the production of mature sperm cells.

Full sperm development occurs in the testes and usually takes about two months for full development.

The male ejaculate contains 100 – 200 million sperm.

This process begins at puberty and continues until death.

Oogenesis

The production of a mature egg characterized by an unequal cytokinesis.

At birth, all primary oocytes for life are present in the body (at least 400,000)

The primary oocytes are ‘frozen’ before they have the chance to complete meiosis .

When a girl goes through puberty, hormones are made that stimulate one ‘frozen’ oocyte (at a rate of 1 per month) to continue meiosis. IF a sperm is present, meiosis will be completed and the sperm will fertilize the new egg.

[Fertilization triggers meiosis to be completed.]

The cycle continues from puberty until menopause.

How many eggs does a woman need?

12 per year for how many years…

35-40 years (at the most) = 420-480 eggs and she starts with 400,000…

The age of the egg = the age of the woman

Spermatogenesis and Oogenesis

SpermatogenesisInvolves meiosisProduces 4 haploid

daughter cellsEach daughter cell develops

into a spermProcess begins at puberty

(sperm are all ‘fresh’)Process ends at deathBillions are produced at a

time.

OogenesisInvolves meiosisCan produce 4 haploid

daughter cellsOne daughter cell becomes

the egg; three polar bodies die

Process begins before birth (eggs are as old as the female)

Process ends at menopause

One egg matures monthly.

When can a woman get pregnant?

The egg is viable for 12-24 hours after it has left the ovary (ovulation)

The sperm is viable for up to 72 hours (although most sperm retain their fertilizing power only for 12 to 48 hours after ejaculation.)

The ‘window of opportunity’ for fertilization – 72 hours prior to ovulation to 24 hours after ovulation. This equates to only 3 to 4 days a month.