Cell Division Cell Division SOL: BIO 6 a-c SOL: BIO 6 a-c
Dec 29, 2015
Cell DivisionCell DivisionSOL: BIO 6 a-cSOL: BIO 6 a-c
MeiosisMeiosis Meiosis occurs in sexual Meiosis occurs in sexual
reproduction when a diploid reproduction when a diploid germ cell produces four haploid germ cell produces four haploid daughter cells that can mature daughter cells that can mature to become gametes (sperm or to become gametes (sperm or egg).egg).
MeiosisMeiosis
Goal: reduce genetic material by halfGoal: reduce genetic material by halfWhy? Why? n (mom) + n (dad) = 2n (offspring)
from mom from dad child
meiosis reducesgenetic content
toomuch!
Just right!
Meiosis: cell division in Meiosis: cell division in two partstwo parts
Chromatidsseparate
Sister chromatidsseparate
Result: one copy of each chromosome in a gamete.
Haploid
Diploid
Meiosis I(reductiondivision)
Meiosis II
Haploid
(equationaldivision)
2n
nn
Meiosis I : the reduction Meiosis I : the reduction divisiondivision
Prophase I(early)
(diploid)
Prophase I(late)
(diploid)
Metaphase I(diploid)
Anaphase I(diploid)
Telophase I(diploid)
Nucleus Spindlefibers
Nuclearenvelope
Prophase IProphase I
Early prophase
Chromatids pair. Crossing over occurs.
Late prophase
Chromosomes condense.Spindle forms.
Nuclear envelope fragments.
Metaphase IMetaphase I
Chromatid pairs alignalong the equator of the cell.
Anaphase IAnaphase I
Chromosomes separate andmove to opposite poles.
Sister chromatids remain Attached at their centromeres.
Telophase ITelophase I
Nuclear envelopes reassemble.
Spindle disappears.
Cytokinesis divides cell into two.
Meiosis IIMeiosis II
Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene.
Sister chromatids carry identical genetic
information.
Gene X
Meiosis II : the equational Meiosis II : the equational divisiondivision
Prophase II(haploid)
Metaphase II(haploid)
Anaphase II(haploid)
Telophase II(haploid)
Four Non-identical
haploid daughter cells
Prophase IIProphase II
Nuclear envelope fragments.
Spindle forms.
Metaphase IIMetaphase II
Chromosomes align along equator of cell.
Anaphase IIAnaphase II
Sister chromatids separateand move to opposite poles.
Telophase IITelophase II
Nuclear envelope assembles.
Chromosomes unravel.
Spindle disappears.
Cytokinesis divides cell into two.
Results of meiosisResults of meiosis
• Four haploid cells
• One copy of each chromosome
“Putting It All Together” - Fertilization
What Meiosis is About
Meiosis allows the creation of unique individuals through sexual reproduction.
Mitosis Meiosis
Number of divisions 1 2
Number of daughter cells
2 4
Genetically identical?
Yes No
Chromosome # Same as parent Half of parent
Where Somatic cells Sex cells
When Throughout life At sexual maturity
Role Growth and repair Sexual reproduction
MITOSIS MEIOSIS
Occurs in somatic (body) cells Occurs only in gonads (sex organs: ovary/testes)
Produces cells for repair,maintenance, growth, asexual reproduction
Only produces gametes (sex cells: egg/sperm)
Results in identical diploid (2n) daughter cells
Reduction division results in haploid (n) cells