Download Bio 200- Lab Lecture 6

Bio 200- Lab Lecture 5
Mitosis and Meiosis
Mitosis:
Cell division that gives 2 daughter cells with identical genetic
information out of a mother cell.
All multicellular organisms develop through a series of mitotic
divisions of a single cell.
Life cycle of a cell: Time beginning from the moment a cell is
formed by mitosis and ending when the cell itself divides by
mitosis producing 2 new daughter cells.
Cell cycle: Brief mitosis + Long interphase
Interphase:
Time between 2 cell divisions
-Cell performs normal activities: metabolism, movement, DNA
replication
Nucleus: DNA in the form of chromatin
Nuclear membrane present
1 or 2 nucleoli
DNA replicates: chromosomes made of 2 sister
chromatids
3 stages in interphase:
G1, S, G2
Mitosis:
4 main phases of mitosis:
1- Prophase
2- Metaphase
3- Anaphase
4- Telophase
-1- Prophase:
- Chromatin condenses into shorter and thicker chromosomes
- Microtubules form the mitotic spindle extending from
centrioles (asters) in animal cells
- Nucleoli disappear
- Nuclear membrane disintegrates at the end of prophase
2- Metaphase:
- Chromosomes attach through the centromere to the spindle
fibers and align at the equator of the cell.
3- Anaphase:
- Centromeres divide
- Chromatids separate and are pulled to opposite poles of the cell
(daughter chromosomes)
4- Telophase:
- Chromosomes at the poles uncoil
- Spindle breaks down
- Nuclear membrane forms around each set of chromosomes
- Nucleoli reappear
- Cytokinesis: Cell plate in plant cells

Cleavage furrow in animal cells
In the lab:
- Obtain a slide showing mitosis in onion root tips, identify
different stages of mitosis
- Obtain a slide showing mitosis in animal cells (ascaris)
- Compare animal and plant mitosis
Meiosis:
Cell division that produces daughter cells with half the number of
chromosomes of the mother cell.
Important in sexually reproducing organisms to maintain the
constant number of chromosomes of a species.
Somatic cells have 2 sets of homologous chromosomes (diploid).
Some of these cells divide by meiosis to produce gametes
(haploid). Upon fertilization, fusion of a male and female gamete
produces a zygote (diploid) which divides by mitosis to produce a
multicellular diploid organism.
Meiosis = 2 cell divisions, Meiosis I and Meiosis II
Meiosis I:
1- Prophase I:
- Chromatin condensation
- Disintegration of nuclear membrane
- Nucleolus disappears
- Homologous chromosome pair with each other (synapsis)
- Exchange of chromatid segments (crossing-over) can occur
during synapsis
2- Metaphase I:
- Chromosomal pairs line up at the equator of the cell
3- Anaphase I:
- Segregation of the homologous chromosomes
- Daughter chromosomes at the poles of the cell are made of 2
chromatids
4- Telophsae I:
- Dauhgter cells form by cytokinesis each with half the number
of chromosomes
Meiosis II:
In each of the 2 daughter cells produced in Meiosis I:
1-Prophase II:
- Spindle fiber forms
- Nuclear membrane disintegrates
- Chromosomes become visible
2- Metaphse I:
Chromosomes (each with 2 chromatids) line up at the equator
3- Anaphase II:
Sister chromatids are pulled apart toward oppsite poles of the cell
4- Telophase II:
- Nuclear membrane reforms
- Nucleoli reappear
- Spindle breaks down
- Chromosomes uncoil
- Cytokinesis in both cells results in 4 daughter cells with half
the number of chromosomes of the mother cell. Each
chromosome is made of 1 chromatid.
In the lab:
- Observe a slide showing different stages of meiosis occurring
in Lily anthers.