Download Phases of Mitosis

Cell Reproduction

Mitosis – asexual reproduction
– 1 cell produces 2 identical cells

Meiosis – sexual reproduction
– 1 parent cell produces 4 cells with ½ the
number of chromosomes as the parent
Why Cells Divide

Growth

Repair

Reproduction
When Cells Divide

Surface Area/Volume Ratio determines
the maximum size of any cell.

Cells can’t get bigger, so they divide.
Terminology
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Parent cells for new daughter cells

Chromosomes contain DNA & genes

Homologous Chromosomes (a pair)
Phases of Mitosis
Interphase
 Chromosomes
are uncoiled
 DNA
replicates
 Centrioles replicate
DIVISION
INTERPHASE
Prophase



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Chromosomes coil - appear double
stranded
Nucleolus & nuclear membrane
disappear
Centromere and chromatids are visible
Centrioles form aster rays & spindle
fibers as they move to the poles
Metaphase
Double stranded chromosomes
individually line up on the equator
 Centromeres attach to a spindle
fiber

CENTROMERE
CENTRIOLE
CHROMATID
Anaphase
 Chromosomes
split & separate
and are pulled to opposite poles
of the cell by the spindle fibers
Telophase
Cytoplasm divides (cytokinesis)
 New nuclear membranes form

Cell Division and Reproduction

Sexual Reproduction
– 2 parents needed.
– Offspring are similar to, but not
identical to the parents.
– Genetic variations contribute to
evolution of species.
Chromosome Number


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Each species has a specific chromosome
number.
Homologous chromosomes - 2 of a same
pair. Have the same number and types of
genes. One from egg, other from sperm.
Gametes - reproductive cells. Have half
the chromosome number. They have only
one chromosome of each pair.
Chromosome Number



Haploid - half chromosome number
Sex cells (n)
Diploid - pairs of chromosomes
Body cells (2n)
Meiosis - reduction division reduces
chromosome number to haploid.
Phases of Meiosis
One DNA replication followed
by two cell divisions.
Interphase I

DNA replicated

Centrioles replicated
Prophase I
Chromosomes coil
 Centrioles move to poles
 Spindle fibers and asters form
 Nuclear membrane disappears
 Homologous chromosomes
synapse & crossing over occurs

Metaphase I

Homologous chromosomes line
up at the equator in pairs

Crossing over occurs between
homologs
Anaphase I

Homologous chromosomes
separate and move to poles
Telophase I

Cytokinesis occurs forming 2
haploid cells

Cells contain double stranded
chromosomes at this point
Interphase II

No DNA replication

Chromosomes uncoil

Centrioles replicate
Rest same as Mitosis

Prophase II - Chromosomes coil.

Metaphase II - Line up on equator.

Anaphase II - Split at centromere
and move to opposite poles.

Telophase II - Cytokinesis results in
4 haploid cells.
Spermatogenesis


Sperm cell formation
4 equal sized gametes form
23
23D
23
46
46D
23
23D
23
Oogenesis

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Egg cell formation
1 large egg + 3 polar bodies (die)
23
23
D
46
46D
23
23
23D
23
Mitosis vs. Meiosis
Mitosis
46
Zygote
Diploid
Cells
Fertilization
23
23D
23
Meiosis
46
23D
Haploid
Cells
23
23
Gametes
23
Genetic Variations

Sexual reproduction (fertilization)

Meiosis - independent assortment
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Meiosis - crossing over
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Random Mutations