Transcript •Power Point 1

Francisco Estrada
Period 2
Differentiation
Mitosis
 Asexual Reproduction
 Prophase: The sister chromatid
pair together to form dyads, but
homologous chromosomes do
not pair together. The events of
crossing over do not take place
during mitosis.
 Metaphase: chromosomal dyads
made up of two sister
chromatids align at the
equatorial plate
Meiosis I
 Sexual Reproduction
 Meiosis consist of two
successive nuclear divisions
Meiosis I and Meiosis II
 Prophase I: Pairing of
homologous chromosomes
occurs leading to the
formation of tetrads, following
by crossing over between
homologous chromosomes.
Differentiation
 Anaphase: Centromeres split
and the sister chromatids are
seperated in this phase. These
sister chromatids are then
pulled towards the opposite
ends, to be assorted into the
daughter cells.
 Telophase: Two genetically
identical daughter cells are
formed marking the end of
mitosis. Genetic variation is not
introduced due to the lack of
crossing over.
 Metaphase I: Chromosomal
tetrads align at the equatorial
plate during metaphase I.
 Anaphase I: the centromeres
remain intact. Chromosomes
separate from their
homologous partners, but the
pairs of the sister chromatids
remain intact during
anaphase I. The pairs split up
during metaphase II.
Differentiation
 Telophase I: Two haploid cells
with duplicate copies of
chromosomes are formed after
telophase I. Telophase II, leads
to the formation of four
genetically distinct haploid cells.
The Important Roles of Mitosis
 Like many things, cells wear out and die. If an organism is to live
and grow it must reproduce. Therefore cell division serves an
important role in an organism's health and growth. Cell division
occurs rapidly in living organisms.
 Mitosis refers to the process by which cells multiply. The
importance is that the process enables your cells to reproduce
and regenerate tissue in the body. Single celled organisms
reproduce in this way.
 It is important that the cells divide and replace old worn out
cells and more importantly be able to replicate the duties of the
cells they replace.
 It is also important for genetic stability. By duplicating the exact
copy of our genetic material it ensures that our genetic material
is stable and able to carry out its function correctly
Regenerating Cells
 It is also important for cell replacement, regeneration.
 An example for cell replacement: a lizard tail is a good example of cells
regenerating when the tail is detached from the lizard body. The lizard
is able to regenerate another one by the process of mitosis.
The Important Roles of Meiosis
 Meiosis performs a key task necessary in a sexual life cycle.
 In animal life cycles, the meiotic cell division in the life cycle
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immediately precedes the development of gametes.
To create gametes that are haploid.
Divides one nucleus into four.
Meiosis reduces the number of chromosomes in half.
Meiosis produces genetically different daughter of nuclei
Meiosis increases genetic diversity, continue evolution, and maintain a
species.
Phases of Mitosis
 Prophase: During prophase you can see the duplicated
chromatids attach to their centromere. Also during
prophase the cells starts to build a spindle, a fanlike
system of microtubulus that will help separate the
duplicated chromosomes. Then the centrioles start to
move toward the opposite poles.
Metaphase
 During metaphase, the centromeres of the duplicated
chromosomes line up across the center of the cell.
Spindle fibers connect the centromeres of each
chromosomes to the two poles of the spindle.
Anaphase
 Anaphase begins when sister chromatids suddenly
separate and begin to move apart.
 The chromosomes separate and move along spindle
fibers to the opposite ends of the cell.
Telophase
 The chromosomes begin to spread out into a tangle of
chromatin. A nuclear envelope re-forms around each
cluster of chromosomes.
 The spindle begins to break apart, and a nucleolus
becomes visible in each daughter nucleus.
Forming New Cells
 Step 1: The cells gets ready for mitosis. The duplicated
chromosomes are held together. Fibers made of protein begin
to form that will eventually help pull the pairs of
chromosomes apart.
 Step 2: The membrane that surrounds the cell’s nucleus brakes
apart and the chromosome duplicates line up at the middle of
the cell. The fibers have become stronger and attach at both
ends of the cell as well as to each chromosome.
Step 3: The thick fibers attached to opposite ends of the cell pull
the duplicated chromosomes apart into two groups.
Step 4: A nucleus membrane forms around both groups of
chromosomes and the rest of the cell begin to divide. With the
same genetic material, these two cells are just like the one they
were made from.
Maintaining Chromosomes
 Mitosis – separation of chromosomes into two identical
sets of daughter cells
 In mitosis chromosomes separates and form into two
identical sets of daughter nuclei, and it is followed by
cytokinesis (division of cytoplasm). In mitosis the mother
cell divides into two daughter cells which are genetically
identical to each other and to the parent cell.
Process of Meiosis
Meiosis I
 Prophase I: Homologous Chromosomes in the nucleus
begin to pair up with one another and then split into
chromatids (one half of a chromosome) where
crossing over can occur. Crossing offer can increase
genetic variation.
 Metaphase I: Chromosomes line up at the equator of
the cell, where the sequence of the chromosomes lined
up is at random increasing genetic variation by
independent assortment.
Anaphase I - The homologous chromosomes move to
opposing poles from the equator
Telophase I - A new nuclei forms near each pole alongside its
new chromosome compliment.
At this stage two haploid
cells have been created from
the original diploid cell of the
parent.
Meiosis II
 Prophase II: The nuclear membrane disappears
and the second meiotic division is initiated.
 Metaphase II: Pairs of chromatids line up at the
equator.
 Anaphase II: Each of these chromatid pairs move
away from the equator to poles from spindle fibers.
 Telophase II: Four new haploid gametes are
created that will fuse with the gametes of the
opposite sex to create a zygote.
This process of meiosis creates
gametes to pass genetic
information from parents to
offspring.
Crossing-Over
 During meiosis, homologous chromosomes are paired
together, there are points along the chromosomes that
make contact with the other pair. This point of contact
is deemed the chiasmata, and can allow the exchange
of genetic information between chromosomes.
Independent Assortment
 Random distribution of maternal and paternal
homologous to the gametes. Random distribution of
genes located on different chromosomes
Formation of Haploid Gametes
 Meiosis results haploid gametes by crossing-over and independent
assortment.
 Independent Assortment:
During Metaphase I the homologous pairs (consisting of one maternal
and one paternal chromosome) are situated at the metaphase plate.
Each pair may orient its maternal or paternal homologous closer to
either pole. Each of the pairs are positioned independently, each side
have a 50% chance of receiving either maternal or paternal
chromosomes.
 Crossing Over:
During Phrophase I homologous chromosomes pair loosely along their
lengths and the exchange of two corresponding segments of two nonsister chromatids (one paternal and one maternal) occurs.
Cancer and Mutation
 The abnormalities in cancer cells usually result from mutations in
protein-encoding genes that regulate cell division. Over time more
genes become mutated. This is often because the genes that make the
proteins that normally repair DNA damage are themselves not
functioning normally because they are also mutated. Consequently,
mutations begin to increase in the cell, causing further abnormalities
in that cell and the daughter cells. Some of these mutated cells die, but
other alterations may give the abnormal cell a selective advantage that
allows it to multiply much more rapidly than the normal cells.