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
informationEx. 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 OrganismsName of Organism Diploid Number Image
Adders-tongueOphioglossum reticulatum
1440This fern has the highest known chromosome number of any life form
Field HorsetailEquisetum arvense 216
Red viscacha ratTympanoctomys barrerae
102 Highest number known in mammals, a tetraploid[3].
Hedgehog
90
Diploid Numbers in other OrganismsName of Organism Diploid Number Image
Turkey
80Dogs, Coyotes, Dingos, and Wolves 78
MuleHorse/Donkey Cross 63 *Infertile
Platypus 5210 Sex Chromosomes
Jack Jumper Ant 2 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
Sex Determination in OrganismsHumans rely on Xs and Ys to determine if it’s a boy or girl, but what about other organisms?
Do male ants have Fathers?
Why are all turtles Hot Chics and Cool Dudes?
Nemo’s dad Marlin should have been Marly?
Questions about Meiosis????
