Mitosis, meiosis and embryo development by pzs15406

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									Mitosis, meiosis and embryo development
• Prokaryotic organisms and most eukaryotic cells in the body
  undergo mitosis

• Mitosis is a means to replace damaged cells, cells that have
  been sloughed off, or to facilitate overall organismal (animal
  and plant) growth

• Different types of cells or tissues have specific cell cycle rates

• Diploid (or 2n) cells start with the normal number of
  chromosomes and end with same number

• For example: Diploid human cells have a total of 46
  chromosomes (23 pairs) and end with 46 chromosomes
            Overview of cell cycle
• All cells start off with a period of growth

• As cells grow in size, they produce organelles, and perform various

• Before cell division, chromatin (DNA) must be replicated

• Chromatin must be coiled up into chromosomes

• Chromosomes consist of a pair of chromatids called “sister

• Each new daughter cell has one chromatid from each pair of
    What was that about chromosomes?
• Chromosomes are a way of
  organizing and condensing        Histones
  very long strands of DNA
• DNA is wrapped around
  histone proteins and many
  histone coils are found in a
                  Stages of mitosis

• The longest phase of the
  cell lifecycle is

• Interphase consists of
  three phases

• Cell division comprises a
  much smaller portion of
  the cell lifecycle
Mitosis: Interphase, and prophase
         Centrioles are assembly points for microtubules

                   Fig. 5.25 (TEArt)


                     Spindle fibers are made of microtubules which act as
Microtubules are     guiding wires to push chromosomes through the cell
made of proteins
Mitosis: Metaphase, anaphase, telophase

Cytokinesis (cell division) occurs during telephase
         Cytokinesis in animal cells
• Note the presence of a cleavage
• Cells are pulled apart by
  microfilaments (protein called actin)
             Cytokinesis in plant cells
• No cleavage

• Cell gradually expands horizontally

• Cell reconstructs cell wall from materials
  found in vesicles

• Cell plate becomes new cell wall
         Recognizing stages of mitosis

Allium root tip
         Recognizing stages of mitosis
Gastrulation from zygote to
      blastula stage          Whitefish blastula


           Mitotic diseases: Leukemia
  (“red” blood cells)
                      Leukocytes                Abnormal leukocytes
                  (“white” blood cells)

Normal human blood smear                  Acute lymphocytic leukemia
            More about cancer
• Cancer cells do not respond to cell cycle control system and
  excessively divide

• A normal cell may transform and become a type of cancer cells
  (such as a tumor) if it escapes detection by the immune system after

• Benign tumors are localized and malignant tumors spread to other
  parts of the body via the blood or lymphatic system

• Chemotherapy drugs interrupt cancer cells during certain phases of

• Radiation treatment attempts to thwart cancer cells by destroying
  cancer cell DNA; cancer cells are typically unable to repair damaged
   More about human chromosomes
• A typical human cell is called a
  somatic cell

• In a somatic cell there are 46
  chromosomes (23 homologous

• 22 of these pairs are autosomes

• 1 pair of sex chromosomes
   XX = Female, XY = Male

• Diploid cells (2n) have 46
                                     Normal human karyotype
• Haploid cells (n) have 23
  chromosomes (22 autosomes and
  1 sex chromosome)
• Meiosis is a means to transfer genetic information onto the next
  generation without doubling the number of chromosomes in each

• Meiosis consists of cell division phases (prophase, metaphase,
  anaphase, telophase) similar to mitosis except there are two meiotic
  cycles (meiosis 1 and meiosis 2)

• Gametes start as diploid cells (2n) end as haploid cells (n), one
  chromosome from each pair

• Meiosis in humans occurs in gametes (egg and sperm)

• When the egg and sperm unite during sexual reproduction, a diploid
  (2n) zygote is produced
Meiosis 1
Meiosis 2
         Gamete production in men
• Sperm cells develop from
primary spermatocytes in
seminiferous tubules

• Primary spermatocytes
differentiate into secondary
spermatocytes after meiosis 1

• Secondary spermatocytes
differentiate into sperm cells
after meiosis 2
               Sperm cell development

Testes consists of chambers
in which sperm are produced
            Gamete production in women
• An ovum develops from an oocyte

• Primary oocyte and first polar body
develops after meiosis 1; first polar
body may also undergo meiosis and
produce 2 polar bodies

• Secondary oocyte and second polar
body develops after meiosis 2

• Presence of sperm completes meiosis
2 causing secondary oocyte to develop
into ovum and one polar body

• Thus, 3 polar bodies and 1 ovum may
be produced after successful
completion of meiosis
Female gamete production and embryo implantation

                            Ovary, oviduct, uterus
                Oocyte development
                               Immature oocytes
• Females are born with
  thousands of oocytes
                                     Developing oocyte

• Oocytes are arrested until
  puberty                                Mature oocyte

• After puberty, oocytes
  begins to mature each
            Embryo development

• After zygote formation, cleavage occurs

• Cleavage consists of a series of rapid cell
  divisions until blastula formation – overall
  embryo size does not change

• A blastula (background) transforms into a
  gastrula through a process known as

• Gastrulation is complete when three embryonic
  germ layers are formed
    Embryo development continued

These cells undergo mitosis   Embryo develops tissue
                              layers which become organs
                              and other structures
YouTube - Amphioxus embryonic

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