Download Mitosis and Meiosis

Mitosis and Meiosis
Mitosis and Meiosis
• Mitosis:
-division of somatic (body) cells
• Meiosis
-division of gametes (sex cells)
Mitosis
1) Interphase
2)Cell division
• Prophase
• Metaphase
• Anaphase
• Telophase
3) Cytokinesis
1) Interphase
• Interesting things happen!
1. Cell preparing to divide
2. Genetic material doubles
2. Cell division
Prophase
•
1.
Chromosome pair up!
Chromosomes thicken and shorten
-become visible
-2 chromatids joined by a centromere
2. Centrioles move to the opposite sides of
the nucleus
3. Nucleolus disappears
4. Nuclear membrane disintegrate
Metaphase
• Chromosomes meet in the middle!
1. Chromosomes arrange at equator of
cell
2. Become attached to spindle fibres
by centromeres
3. Homologous chromosomes do not
associate
Anaphase
• Chromosomes get pulled apart
1. Spindle fibres contract pulling
chromatids to the opposite poles of
the cell
Telophase
•
1.
2.
3.
4.
5.
Now there are two!
Chromosomes uncoil
Spindle fibres disintegrate
Centrioles replicate
Nucleur membrane forms
Cell divides
3) Cytokinesis
• Division of cytoplasm
• Division of cell into two
daughter cells
Meiosis
1) Interphase
2)Cell division
• Meiosis I (Prophase I, Metaphase I,
Anaphase I, Telophase I)
• Meiosis II
(Prophase II, Metaphase
II, Anaphase II, Telophase II)
3) Cytokinesis
Meiosis
is the process by which ”gametes” (sex cells) , with half the
number of chromosomes, are produced.
During Meiosis diploid cells are reduced to haploid cells
Diploid (2n)
 Haploid (n)
If Meiosis did not occur the chromosome number
in each new generation would double…. The
offspring would die.
1) Interphase
• Similar
to
interphase.
mitosis
Meiosis I (four phases)
• Cell division that reduces the
chromosome number by one-half.
• four phases:
a. prophase I
b. metaphase I
c. anaphase I
d. telophase I
Prophase I
• Longest and most complex phase.
• 90% of the meiotic process is spent in Prophase I
• Chromosomes condense.
Prophase I
spindle fiber
centrioles
Metaphase I
• Shortest phase
• Chromosomes align on
middle of spindle fibers.
the
Metaphase I
OR
metaphase plate
metaphase plate
Anaphase I
• Homologous
chromosomes
separate and move towards the
poles.
• Sister
chromatids
remain
attached at their centromeres.
Anaphase I
Telophase I
• Each pole now has haploid
set of chromosomes.
Telophase I
3) Cytokinesis
Cytokinesis occurs and
two haploid daughter
cells are formed.
Meiosis II
• No interphase II
(no more DNA replication)
• Remember: Meiosis
similar to mitosis
II
is
Prophase II
• same as prophase in mitosis
Metaphase II
• same as metaphase in mitosis
metaphase plate
metaphase plate
Anaphase II
• same as anaphase in mitosis
• sister chromatids separate
Telophase II
• Same as
mitosis.
• Nuclei form.
telophase
in
Telophase II
3) Cytokinesis
• Cytokinesis occurs.
• Remember: four haploid
daughter cells
produced.
gametes = sperm or egg
Meiosis and sex chromosomes
 Sex chromosomes carry genes that determine sex (gender)
 In humans, females have two X chromosomes. But human
males have one X chromosome and one Y chromosome
 During meiosis, one of each of the chromosome pairs ends up
in a sex cell. Females have two X chromosomes in each body
cell. When meiosis produces the egg cells, each egg gets one X
chromosome
 Males have both an X chromosome and a Y chromosome in
each body cell. Meiosis produces sperm with either an X or a Y
chromosome
 An egg fertilized by a sperm with an X chromosome will
produce a female. If the sperm contains a Y chromosome, the
offspring will be male.
Meiosis and sex chromosomes
Sex linked disorders
The Y chromosome does not carry all of the genes of
an X chromosome
Females have two X chromosomes, so they carry two
copies of each gene found on the X chromosome. This
makes a backup gene available if one becomes
damaged.
Males have only one copy of each gene on their one X
chromosome. The genes for certain disorders, such as
color blindness, are carried on the X chromosome.
These disorders are called sex-linked disorders.
Because the gene for such disorders is recessive, men
are more likely to have sex-linked disorders