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• How many chromosomes are in a human body cell?• How many are in a sperm cell? Egg cell?• How are these chromosome numbers reduced?• Why do they need to be reduced?

C. COMPARING & CONTRASTING MEIOSIS AND MITOSIS

MITOSIS MEIOSIS*Asexual repro *Sexual repro*Used for growth + *Used to make repair of body cells sperm + egg*2 daughter cells *4 daughter cells*1 division *2 divisions*daughter cells identical *daughter cells in # of chromosomes have one half*no variation (clones) *much variation

Use the following terms to review mitosis and meiosis:

•Haploid

•Diploid

•Gonads

•Homologous

•Replicate

•Tetrad

•Synapsis

•Crossing Over

•Identical

•Variation

•Disjunction

•Gametes

D. MEIOSIS IN MALES

• is called spermatogenesis

• The male gonads called testes produce male gametes called sperm.

• Primary sex cells in the testes use meiosis to produce the 4 monoploid spermatids which usually mature into 4 motile sperm cells

A fertile young man makes around 1000 new sperm per second, in the testes. Each carries half the instructions (genes) needed to make a new person, packed into its head. The rest of the cell is a long tail, which propels the sperm towards the egg at about three millimeters per minute. The neck is crammed with mitochondria, which help make the energy needed for the journey. Once they're released, sperm usually survive for 48 hours.

Human sperm.Dr Joyce Harper/Wellcome Photo Library

E. MEIOSIS IN FEMALES• is called oogenesis• The female gonads called ovaries

produce female gametes called ova (eggs).

• Primary sex cells in the ovaries use meiosis to produce eggs.

• An ovum is larger than a sperm cell because ova contain yolk, which is food for the developing embryo

• Unlike spermatogenesis, oogenesis only produces 1 monoploid egg while the other 3 cells do not receive enough cytoplasm, and disintegrate; they are called polar bodies

• Oocyte development stops at the primary oocyte during development of the female embryo and only resumes at puberty… only 1 ovum per month

An egg cell is 150 um in size, and is colorless and semi-transparent. It is the

shape of a sphere and its outer part is surrounded by a soft yet tough membrane. Within the structure of the egg there are extra nutrients like fat, sugar and proteins. This reserve of nutrients will ensure that the egg cell is nourished on its journey and, if fertilization occurs, will take care of its needs until it reaches the uterus.

Chunk• What is meiosis in males called?• What are the male gonads and gametes?• How many sperm are produced per spermatocyte?• Are sperm haploid or diploid?• What is in the neck of the sperm?• How long does it survive?• What is meiosis in females called?• What are the female gonads and gametes?• Why is the ovum larger than a sperm?• How many eggs does oogenesis produce per oocyte?• Are eggs haploid or diploid?• What are the 3 cells that disintegrate called?• Explain the pause in development of oocytes. • Give 3 ways spermatogenesis is different from oogenesis.

That’s all folks!

Image Sources• Red and blue - bio.rutgers.edu/.../meiosis_web/intropage.html • Comparison diagram - library.thinkquest.org/.../cell%20division.htm • Spermatogenesis + Oogenesis - www.bio.miami.edu/.../animal_development.htm • Sperm - www.ub.es/humangen/index_archivos/image001.jpg • Sperm clipart - www.canstockphoto.com/illustration/sperm.html • Egg - www.creationofman.net/.../yaratilis219.jpg