mitosis and meiosis

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Mitosis and Meiosis Done by: Rawan Walid shahien

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Mitosis and meiosis

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Page 1: Mitosis and meiosis

Mitosis and MeiosisDone by: Rawan Walid shahien

Page 2: Mitosis and meiosis

Mitosis

Page 3: Mitosis and meiosis

Interphase

Interphase: Nuclear envelope

still there And its before S

phase because the centrioles arent duplicated yet

Page 4: Mitosis and meiosis

Prophase

The chromatin condensed together to create visible chromosomes.

Page 5: Mitosis and meiosis

Prophase

The spindle fibers also begin to form

Migration of the two pairs of the centrioles to the opposite sides of the cell.

Thinning and gradual disappearance of nuclear envelope.

Page 6: Mitosis and meiosis

Prophase

Gradual mixing of the nucleolus with the rest of the nucleus.

The nuclear envelope is almost completely disappeared

Page 7: Mitosis and meiosis

Metaphase

Metaphase is marked by the alignment of all the chromosomes at the equatorial plane of the cell (the metaphase plate).

The nuclear membrane dissolves completely, marking the beginning of metaphase.

Attachment of the the spindle fibers to the centromere of the chromosome at a point called kinetochore.

Page 8: Mitosis and meiosis

Anaphase

Movements of the chromosomes occurs due to shortening of spindle microtubules and kinetochore movement along the spindle fibers.

Page 9: Mitosis and meiosis

Anaphase

Migration and arrival of the new chromosomes to the opposite poles of the cell.

Page 10: Mitosis and meiosis

Telophase

During this stage, daughter chromosomes arrive at opposite poles of cell and the spindle fibers disappear.

The chromosomes change into chromatin and become invisible under the light microscope.

Nuclear envelope begins to form around the new nuclei.

Page 11: Mitosis and meiosis

Cytokinesis that takes place during telophase

Cytokinesis or cleavage of the cytoplasm of the cell begins.

Page 12: Mitosis and meiosis

The result

myosin molecular motors attach to the actin and draw the membrane in -like a purse string.

Once the sister chromatids are separated, a ring of actin filaments (microfilaments) form a “contractile ring” around the middle of the cell

By the end of telophase, two independent daughter cells have been formed

Page 13: Mitosis and meiosis

Meiosis

Page 14: Mitosis and meiosis

Interphase

Interphase: “ before S phase”

1. the nuclear envelope still there

2. the chromosomes aren't condensed yet

3. Replication of centrioles didn’t occur

Page 15: Mitosis and meiosis

Interphase

Interphase: “ after S phase”

1. the nuclear envelope still there

2. the chromosomes started to condense

3. Replication of centrioles took place

Page 16: Mitosis and meiosis

Prophase 1 Early prophase 1: The chromatin condensed

together to create visible chromosomes.

The spindle fibers also begin to form at this time.

And centrioles begun to move away from each other

The maternal and paternal homologous chromosomes come close to each other and then align

Disappearance of the nuclear envelope is happening gradually

Page 17: Mitosis and meiosis

Prophase 1

Prophase 1: Same as the previous

slide except that The two homologous chromosome now consists of four chromatids, so these chromosomes are called TETRAD.

And now they are connected at the chiasma

Page 18: Mitosis and meiosis

Prophase 1

Late prophase 1: Crossing over takes

place between the tetrad at the Chiasma *crossing over of segments of chromatids*

Page 19: Mitosis and meiosis

Metaphase 1 Metaphase1: The homologous paired

chromosomes are shown to be connected by a terminal chiasma and arranged in the equatorial plate.

The mitotic spindle fibers connect the centromere of each chromosome on one side and the pole of the dividing cell on the other side

Attachment of the the spindle fibers to the centromere of the chromosome at a point called kinetochore.

Nuclear envelope is disappearing

Page 20: Mitosis and meiosis

Anaphase 1 The terminal chiasma disappears

and the chromosomes become free from each other.

The centromere remains undivided so sister chromatids move together to the opposite poles of the cell.

This movement occurs due to shortening of spindle microtubules and kinetochore movement along the spindle fibers.

Migration and arrival of the new chromosomes to the opposite poles of the cell.

Imp: here seperation of the chiasma takes place but NO division of centromere so the sister chromatids don’t separate here

Page 21: Mitosis and meiosis

Telophase During this stage,

cytokinesis occurres by contraction of actin filaments around the center of the cell which gives two daughter cells.

The chromosomes become thinner and then changed to chromatin.

The nuclear envelope reforms and the nucleolus reappears

Page 22: Mitosis and meiosis

Interkinesis

The two daughter cells that resulted from the 1st meiotic division have 23 (1n) chromosomes and (2C) DNA.

These cells pass in a short interphase called interkinesis during which duplication of centrioles occurs but no replication to DNA takes place (NO S Phase).

Check in the next slide we have two yellow structure which is the centrioles so before we start meiosis 2 centrioles must be duplicated

Page 23: Mitosis and meiosis

Meiosis 2

› no further replication occurs

› chromosomes line up again (metaphase II)

› sister chromatids separate (telophase II and anaphase II)

› the cells divide and chromosomes decondense (cytokinesis, telophase II)

Page 24: Mitosis and meiosis

The result

Four haploid cells * gamete cells* in which 2 are parental , and 2 are recombinant due to crossing over

Page 25: Mitosis and meiosis

The end =D

Wish you the best of luck and inshallah we will all do good in the exams and pass and get HIGH grades =)

You are the best future dentists <3