mrs. stewart biology i standard. review: cell cycle interphase g1, s, and g2 m-phase (mitosis)...
TRANSCRIPT
MITOSIS VS. MEIOSISMrs. Stewart
Biology I standard
REVIEW:Cell Cycle
Interphase G1, S, and G2
M-phase (mitosis) P-M-A-T-C
MitosisAsexual reproductionProduces 2 identical daughter cellsDaughter cells are diploidDaughter cells are identical to parent/mother cell
What differences can you see?
• How many sets of chromosomes are in the cells that Meiosis produces?
• How many cells does Meiosis produce?
• How many divisions occur in Meiosis?
MEIOSIS:The process of creating a gamete
Chromosomes come in matching sets-these are called homologous pairs
Karyotype after DNA replication
Notice how each chromosome has duplicated itself.
Somatic cells in your body have two sets of chromosomes -
they are called DIPLOID
Gametes (Sex cells-sperm and eggs) only have one set (half) of chromosomes - they are
called HAPLOID
Final Products:
Mitosis
Meiosis
Phases of Meiosis IProphase IMetaphase IAnaphase ITelophase ICytokinesis
Interkinesis
Phases of Meiosis IIProphase IIMetaphase IIAnaphase IITelophase IICytokinesis
What are the steps?
InterphaseDNA replicates
Makes the diploid (2n) cell now be (4n)
n=number of chromosome sets/pairs
Example: humans have 46 total chromosomes, so our diploid number is 2n or 2(23) where n = 23
Prophase I
• Homologous chromosomes pair up (forming a tetrad) - Mom & Dad go on a date
• Crossing over occurs
• Chromatids MAY exchange portions of DNA
• Leads to genetic variances
Metaphase ISpindle fibers attach to the chromosomes Homologous chromosomes line up in the
middle of the cell
Anaphase I• Fibers pull the homologous chromosomes toward opposite ends of the cell
Telophase I and Cytokinesis• Nuclear membranes form• Cell separates into two new cells
Meiosis IIThe daughter cells from Meiosis I divide again WITHOUT replicating their chromosomes
That leads to 4 gametes, each with half the number of chromosomes (haploid) as the original “mother” cell
Metaphase IISpindle fibers attach to the chromosomes chromosomes line up in the middle of the cell
– similar to how they do in Mitosis
Anaphase II• Fibers pull the sister chromatids toward opposite ends of the cell
Telophase II and Cytokinesis• Nuclear membranes form• Both cells separate – forming 4 new haploid cells
Oogenesis – meiosis in human female reproductive cells – makes eggs (ovum)
• Forms one egg cell with a large supply of stored nutrients.
• The other 3 gametes produced, called polar bodies, disintegrate.
Spermatogenesis – meiosis in human male reproductive cells to make sperm (spermatazoa)
• Produces 4 viable gametes
• All 4 gametes produce a long whip-like tail
Meiosis:Cell division necessary for sexual
reproductionProduces 4 daughter cellsDaughter cells are Haploid Daughter cells are gametes (sexual repro.
cells)2 nuclear/cellular divisions Vital to maintain correct number of offspring
in sexually reproducing organismsCrossing over = opportunity for genetic
variability
DifferentiateMitosis Meiosis
Asexual reproductionProduces 2 daughter
cellsDaughter cells are
diploidDaughter cells are
identical to each other and to parent cell
Produces somatic cells
One cell/nuclear division
Used for sexual reproduction
Produces 4 daughter cellsDaughter cells are
Haploid Daughter cells are
genetically different from each other, and from parent cell
Produces gametesTwo nuclear/cellular
divisions
Human chromosomal diseasesDown’s syndrome (extra chromosome #21)Turner’s syndrome (missing or incomplete X chromosome
in girls)Klinefelter’s syndrome (males that have an extra X
chromosome [XXY])
**Mistake in meiosis can lead to an incorrect chromosomal number, causing consequences for offspring**
VideoMeiosis square dance