Cell Cycle and Chromosomes

Cells are active in lag phase. They are rapidly synthesising new protoplasm. They are synthesising enzymes or coenzymes for operation of the chemical machinery of cell.

After the mitotic cell division of oogonia stops, the cells formed are known as oocytes.

Oogonia divides by repeated mitotic divisions.

Primary oocyte increases in size during the growth phase.

There are 3 polar bodies produced in the process of oogenesis.

Meiosis takes place in ootidogenesis.

Egg contains 2X chromosomes.

Human males have XY sex chromosomes, while females have XX. The Y chromosome carries the SRY gene that triggers male development. YY is not viable in humans, XO causes Turner syndrome, and XX is the female karyotype.

A relatively rigid cell wall outside the cell surface membrane has pores containing fine threads known as plasmodesmata, which link the cytoplasm of neighbouring cell through the cell walls.

C. B. Bridges (1925) reported his balance theory of sex determination in Drosophila.

Gametes are haploid (n) and contain half the DNA content of somatic cells which are diploid (2n). This 1:2 ratio results from meiosis which reduces chromosome number by half.

All of the above cause chromosomal mutation.

It involves change in chromosome number that is an exact multiple of monoploid. Thus, it involves addition or deletion of one set of chromosomes.

Individuals with three sets of chromosomes; 2n + n = 3n

Loss of a pair of chromosome from a diploid set