Meiosis is a process that reduces the amount of chromosomes in a cell to half the original amount Why would you want to reduce chromosomes to half? (check with your neighbor)

Egg = 23 Sperm = 23 Egg + Sperm = 46 in them. If meiosis reduces the chromosome number in half, how many chromosomes are in human sex cells?

Haploid (n)– a half set of chromosomes Diploid (2n) – a full set of chromosomes Somatic Cells = ALL body cells (blood, skin, etc) except gametes

Gamete Skin Cell Egg Somatic Cell Sperm Sex Cell Haploid or Diploid?

Homologous Chromosomes – chromosomes that have the same information Ex. Father/Paternal #11 chromosome Mother/Maternal #11 chromosome “Partner” up in Prophase 1

Crossing Over is the exchange of genetic material between homologous chromosomes Crossing Over acts as a source of genetic variation within a species

Stages of Meiosis Interphase — 1 time ONLY –Growth and replication of DNA PMATC— 2 times –Prophase, Metaphase, Anaphase, Telophase, Cytokinesis

Diploid Cell—2 copies of each chromosome that replicated during Interphase

Crossing Over occurred during Prophase 1

Anaphase AWAY

Telophase I/Cytokinesis results in 2 Haploid Cells

Prophase II looks similar to Telophase I, but nuclear envelope is disappearing again

Anaphase Away—part II

Telophase II and Cytokineses results in 4 HAPLOID sex cells….or gametes….or egg….or sperm!

What’s different?

Egg (Ovum) is created in the Ovary

Sperm is created in the Testis

Diploid Numbers in other Organisms Name of OrganismDiploid NumberImage Adders-tongue Ophioglossum Ophioglossum reticulatum 1440 This fern has the highest known chromosome number of any life form Field Horsetail Equisetum arvense 216 Red viscacha rat Tympanoctomys barrerae 102 Highest number known in mammals, a tetraploid [3]. [3] Hedgehog 90

Diploid Numbers in other Organisms Name of OrganismDiploid NumberImage Turkey 80 Dogs, Coyotes, Dingos, and Wolves 78 Mule Horse/Donkey Cross 63 *Infertile Platypus Sex Chromosomes Jack Jumper Ant2 for females, 1 for males

Karyotype – a “map” of chromosomes 2 Main Uses: Determine sex of the baby Screen for Chromosomal Abnormalities Ex. Down Syndrome

22 pair of Autosomes + 1 pair of sex chromosomes = 23 Total pairs XX = Female XY = Male

Questions about Meiosis????

Quiz What are sex chromosomes called? How many chromosomes does a diploid cell have? Haploid? What is a karyotype used for?

Quiz What is the purpose of crossing over? What does meiosis in male gametes create?? What does meiosis female gametes create?