Karyotyping And Cell Division

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It give idea about Procedure of Karyotyping as well as Cell division

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KARYOTYPE AND IDIOGRAM :

KARYOTYPE AND IDIOGRAM

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Karyotype is a complete set of metaphase chromosomes arranged in pairs, on the basis of size, centromere position and shape. In a karyotype, chromosomes are arranged and numbered by size from largest to smallest. This arrangement helps in quickly identify chromosomal alterations that may result in a genetic disorder.

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For making karyotype, to take the picture of chromosome, cut and match every chromosomes on the basis of size, banding pattern and centromere position. Avian karyotype is different from mammalian karyotype because of presence of very small autosomes called microchromosomes .

Use of Karyotyping:

Use of Karyotyping It permits an accurate count and characterization of chromosomes of an individual/species It permits rapid identification of chromosomal abnormalities, particularly those involving structural changes Idiogram Idiogram is the diagrammatically representation of the chromosomes arranged in descending order of length. Or The karyotype can be represented diagrammatically with all the morphological features of chromosomes, such a diagram is known as idiotype .

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5 CELL PREPARATION Culture cells until sufficient mitotic activity Add colchicine to arrest in metaphase Add hypotonic salt solution to swell cells Fix with mix of methanol: acetic acid

Normal karyotype of cattle [2N = 60, XY]:

Normal karyotype of cattle [2N = 60, XY] 6

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7 Karyotypes of Murrah buffalo, an Indian dairy breed [2n=50] Karyotypes of Asiatic swamp buffalo in Thailand [2n=48]

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NORMAL KARYOTYPE of DOG [ 2N = 78,XY ] All autosomes are acrocentric The sex-chromosomes are metacentric

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9 NORMAL KARYOTYPE of CAT [2N = 38,XY] They are all metacentric

NORMAL KARYOTYPE of SWINE [2N=38,XX] :

NORMAL KARYOTYPE of SWINE [2N=38,XX] Swine have 6 pairs of acrocentric chromosomes and 12 pairs of metacentric autosomes. The X-chromosomes are also metacentric. 10

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11 The horse has 18 pairs of acrocentric and 13 pairs of metacentric autosomes, the X- and Y-chromosomes are also metacentric. NORMAL KARYOTYPE of HORSE [2N= 64,XX]

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12 The ass has 62 chromosomes which are quite different from the ones of the horse. The mule is an infertile cross between the horse and the ass. NORMAL KARYOTYPE of ASS [2N= 62,XX]

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Chromosomal Banding:

Chromosomal Banding   It is process, in which chemical treatment given to metaphase chromosomes and which would be visible in alternative lighter and darker band. Various types of bandings are: G – banding C – banding Q – banding R - banding T – banding NOR - banding

Lampbrush chromosomes :

Lampbrush chromosomes It was first observed by W. Flemming in 1882. It consists of an axis from which paired loops extend in opposite directions, giving the appearance of a lamp brush. Hence the name Lamp Brush Chromosomes. It is found in the Oocytes of amphibians and in some insects. It is larger in size, So it is called a giant chromosome.

Holocentric chromosomes :

Holocentric chromosomes The chromosomes with a non-localized centromere are called as either holocentric or holokinetic chromosomes

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Species 2n Autosomes X Chromosome Y Chromosome Sm / m A Swamp Buffalo 48 10 36 A A River Buffalo 50 10 38 A A Zebu Cattle 60 - 58 Sm Sm Exotic Cattle 60 - 58 Sm A Sheep 54 6 46 A Sm Goat 60 - 58 A Sm Pig 38 24 12 Sm m Dog 78 - 76 Sm Sm Horse 64 26 36 Sm m Donkey 62 38 22 Sm m Chromosome number and morphology in some species of animals:

Cell Division:

Cell Division

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The division of chromosome and cytoplasm of a cell into two daughter cells is known as cell division . The cell cycle or cell-division cycle is an ordered series of events that take place in a cell, leading to cell growth and its division and duplication (replication into two daughter cells). Cytokinesis is the physical division of the cytoplasm whereby the nuclei, cytoplasm, organelles and cell membrane of a single eukaryotic cell is divided into two daughter cells containing roughly equal shares.

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There are mainly two types of cell division: Mitosis Meiosis. The various events occurring during cell division may be grouped in to two categories: Karyokinesis Cytokinesis . Karyokinesis is the division of chromosome of a cell in to two daughter nuclei. Cytokinesis is the division of cell in to two halves to produce two daughter cells. (As a rule, Cytokinesis follows Karyokinesis ) .

Types of Cell Division:

Types of Cell Division Mitosis The mitotic cell division was first described by Flemming in 1879. Somatic cells of all organisms divide through mitosis . Mitosis produces two daughter cells that are identical to the parent cell . This type of cell division allows organisms ( multicellular ) to grow and repair damaged tissue . Meiosis Meiosis (double cell division) produces daughter cells that have one half the number of chromosomes as the parent cell . Meiosis is necessary in sexually-reproducing organisms because the fusion of two gametes (fertilization) leads to doubles the number of chromosomes .

MITOSIS:

MITOSIS Mitosis is a process of nuclear (karyokinesis) and cytoplasmic (cytokinesis) division in which two daughter cells are produced that has chromosomal numbers identical to the parental cell . Mitosis ( M Phase ) is part of the total cell cycle for cells undergoing division. The initial event in the cell cycle is the growth phase, called Interphase .

Slide24:

INTERPHASE The interphase is much longer phase of cell cycle , where the cell prepares itself for cell division. Interphase is divided into three phases: G 1 (first gap) S (synthesis) G 2 (second gap) During all three phases of Interphase , the cell grows and engaged in high metabolic activity to prepare its for mitosis.

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G1 PHASE In this phase, the cell increases in mass and prepares for DNA replication . The metabolic rate of the cell will be high . It takes about 10 hours .   S PHASE DNA replication . Cells will take 5 to 6 hours to complete S phase.   G2 PHASE The cell undergoes of rapid growth to prepare for mitosis . G 2 is shortest subphase of interphase and it lasting only 3 to 4 hours . G 2 phase is after DNA synthesis but prior to the start of prophase of mitosis .

STAGES OF MITOSIS:

STAGES OF MITOSIS Mitosis is divided into, Prophase Metaphase Anaphase and Telophase

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The first phase of mitosis . Chromosomes become condenses and each chromosome has two chromatids joined at a centromere. The mitotic spindle initially appears as structures called asters which surround each centriole pair. The two pair of centrioles move away from one another toward opposite ends . Prophase

Metaphase:

Metaphase Spindle fibers attached to all chromosomes at the kinetochore( centromere region on the chromosomes where sister chromatids are joined ) . The chromosomes begin to migrate towards the center of cell . The condense chromosomes arrange in a line near the center of the cell, that position is called as Equatorial plane or Metaphase plate

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The nuclear membrane disappears completely. Chromosomes align at the metaphase plate (equatorial plate) at right angles to the spindle poles .

Anaphase:

Anaphase Spindle fibers shorten, the kinetochores separate and centromeres of each chromosome begin to move apart to the cell poles . Once the paired sister chromatids separate from one another, each is considered a "full" chromosome (d aughter chromosomes).

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Through the spindle apparatus, the daughter chromosomes move to the poles at opposite ends of the cell. At the end of anaphase, each pole contains a complete compilation of chromosomes.

Telophase:

Telophase Telophase is last phase of mitosis. (Latin word telos which means ' end ‘). The daughter chromosomes arrive at the poles and nucleus begin to form at opposite poles . The nuclear envelopes of these nuclei are re- formed and reappear . Nucleolus also reappear .

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Chromatin fibers of chromosomes uncoil . The spindle fibers also disappear . The chromosomes begin to decondense and become more diffuse.

CYTOKINESIS :

CYTOKINESIS Cytokinesis is the division of the cell's cytoplasm and organelles . With the two nucleus at opposite poles of the cell, the cell cytoplasm separates, ultimately leading to cleavage. At the end of cytokinesis, there are genetically identical two daughter cells .

Time Duration:

Time Duration 18-24 hours at 37  C temperature 95 % time during interphase and only 5 % during mitosis Among mitosis: prophase takes 40 -50 % of total time Anaphase is shortest in duration.

Slide38:

Leland H. (Lee) Hartwell, Tim Hunt and Sir Paul M. Nurse were awarded the Nobel Prize in Physiology or Medicine in 2001 for their discoveries of key regulators of the cell cycle.

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Thank You

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