phases of mitosis

1. prophase- it is the first phase of mitosis. the changes in this phase are that the nucleolus and nuclear membrane disappear, the centrioles divide to form asters and start migrating to either pole of the cell. Lastly, the chromatin fibres condense to form chromosomes.
2. metaphase- in this phase the asters have fully settled at the poles. the chromosomes align themselves on the equatorial plane of the cell
3. anaphase- in this phase the chromosomes are divided longitudinally and move to either side of the cell due to the contraction and expansion of the spindle fibres.
4. telophase- it is the opposite of prophase. the chromosomes become chromatin fibres, the nuclear membrane and nucleolus reappear. the asters return to their original form of centrioles

now the cell is ready for cytokinesis. a division is formed outside the cell at the equatorial plane, and in animal cells, the constriction is formed centripetally.

interphase

it is the phase of growth before karyokinesis. no actual activity regarding cell division takes place hence also called the resting phase.

g1- organelles like the mitochondria and the ribosomes are multiplied

s- genetic material is multiplied

g2- growth phase, protein synthesis

meiosis

it is called reductional division and it occurs in the gametes of the human body- the ova and sperm cell. the sperm and ova only have half the genetic content of a regular human cell as the fertilize and form a zygote with the regular chromosome number.

this division forms 4 daughter cells out of which two fuse together to form a zygote with diploid number 2n.

• in meiosis the two homologous chromosomes are connected at the centromere where the genetic material is exchange this leads to variation in the offsprings
• synapsis is simply the lateral association of two homologous chromosomes.

differences & significance of meiosis and mitosis

pyrimidines- cytosine and thyamine

purines- adenine- guanine