Meiosis

• Organisms that reproduce sexually have specialized cells called gametes (sex cells)

• Gametes are the result of a type of cell division called meiosis

Diploid and haploid

• Almost all human cells are diploid or containing two homologous sets of chromosomes

2n = 46• Eggs and sperm cells (gametes) are haploid or

containing a single set of chromosomes n = 23

ORGANISM (Genus species) NUMBER OF CHROMOSOMES Homo sapiens (human)______________________________46

Mus musculus (house mouse)_________________________40

Drosophila melanogaster (fruit fly)_____________________8

Caenorhabditis elegans (microscopic roundworm)_________12

Saccharomyces cerevisiae (budding yeast) ______________32

Arabidopsis thaliana (plant in the mustard family) ________10

Xenopus laevis (South African clawed frog)______________36

Canis familiaris (domestic dog)________________________78

Gallus gallus (chicken) ______________________________28

Zea mays (corn or maize)____________________________20

Muntiacus reevesi (the Chinese muntjac, a deer) _________23

Muntiacus muntjac (its native american cousin) __________6

Myrmecia pilosula (an ant) ___________________________2

Parascaris equorum var. univalens (parasitic roundworm)___2

Cambarus clarkii (a crayfish)__________________________200

Equisetum arvense (field horsetail, a plant)______________216

Horsetail

HUMAN KARYOTYPE

A display of all the 46chromosomes of an Individual.

9.5 page 2

Remember Mitosis?

MITOSIS

Meiosis

In the human life cycle a haploid egg and sperm fuse and form a diploid zygote. Mitosis produces an embryo with numerous cells that continue to multiply and develop.

haploid egg and sperm

diploid zygote

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio17.swf::Comparison%20of%20Meiosis%20and%20Mitosis

2n

2n 2n

MITOSISMEIOSIS

Original diploid cell

2 diploid daughter cells

Genetic variation is a result of two processes that occurs during meiosis:

• Independent assortment of chromosomes, and • Crossing over

NOTE: Mutations (random changes in gene sequences) are a cuse of genetic variation.

• During metaphase I, the independent assortment of chromosomes that end up in the resulting cells occurs randomly

• Crossing over: exchange of genetic material between homologous chromosomes during prophase I of meiosis

• Genetic recombination: new combination of genetic information in a gamete as a result of crossing over during prophase I of meiosis

(pages 195, 200, & 201) MITOSIS MEIOSIS

TYPE OF CELL (that undergoes this division)

# OF CELL DIVISIONS

Starts/ends as diploid or haploid cell

# OF DAUGHTER CELLS

# OF CHROMOSOMES AFTER DIVISION

EXCHANGE OF DNA (Y/N)

UNIQUE OR IDENTICAL CELL AFTER DIVISION

Development of egg and spermhttp://www.sparknotes.com/testprep/books/sat2/biology/chapter7section2.rhtml