Two types 1.Mitosis - Cell division by which body grows or replaces dead\injured tissue. - Occurs in somatic cells. - Each cell division gives rise to 2 identical daughter cells with chromosomes of the parent cell.(46chr.2n) CELL DIVISION 2.Meiosis – Cell division for reproduction. - Occurs in reproductive cells only. - Each cell division gives rise to 4 nonidentical reproductive cells or gametes with haploid chromosomes oocyte spermatocyte
Abnormal disjunction of chromosomes leads to abnormalities like trisomy or monosomy.
Common examples –
Trisomy 21 – Down’s syndrome
Trisomy 18 – Edward’s syndrome
Trisomy 13 – Patau’s syndrome
Monosomy – 45X – Turner’s syndrome - the only monosomy compatible with life
MITOSIS MEIOSISMitosis requires one division
Meiosis requires two divisions
Two diploid daughter cells result from mitosis
Four haploid daughter cells result from meiosis
Daughter cells are genetically identical to parental cells
Daughter cells are not genetically identical to parental cells
Occurs in all somatic cells for growth and repair.
Occurs only in the reproductive organs for the production of gametes.
In the mitotic cell cycle the interphase consists of all the following phases excepta.G1 b.Mitotic c.S (DNA synthesis)d.G2
Prophase of mitosis consists of all of the following execpta.Visibilty of chromsomesb.Degenration of nuclear membranec.Duplication of centrioled.Formation of mitotic spindle
All are true for metaphase of mitosis excepta.Chromosomes have reached their maximum contractionb.Spindle of microtubules is formedc.Chromsomes reach the equatorial planed.Disjunction (splitting) of chromsomes takes place
Which of the following is a major characteristic of meiosis Ia.Splitting of centromereb.Reducing the amount of DNA to 1Nc.Achieving the haploid number of chromosomesd.Producing primordial germ cells
During meiosis large segments of DNA are exchanged. What is the process called?