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