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 46
chromosomes of an
Individual.
9.5 page 2
Remember Mitosis?
MITOSIS
Meiosis
haploid egg and sperm
diploid zygote
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.
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
MEIOSIS
MITOSIS
Original diploid cell
2n
2n
2n
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)
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
MITOSIS
MEIOSIS
Development of egg and sperm
http://www.sparknotes.com/testprep/books/sat2/biology/chapter7section2.rhtml