Cell Division

Question 1

Review of the structure of chromosomes

Answer 1

At the beginning of the cell division (mitosis and Meiosis), the chromatin network unwinds to forms separate string like structures called chromosomes
A short sequence of nucleotides which carries the genetic code for the development of a particular characteristic or trait is called a gene

Question 2

Chromosomes in Somatic Cells and Sex Cells

Answer 2

Each body cell or Somatic Cell of every organism has its own distinct number of chromosomes. Somatic cells, are all the cells in the plant or animal body besides the Sex Cells
The chromosomes are arranged in pairs, in humans there are 23 pairs of chromosomes
There are 22 different pairs of chromosomes called autosomes and a pair of Sex Chromosomes/ gonosomes
The autosomes are numbered as chromosome number 1,2,3 up to chromosomes number 22, and there are two of each. The two chromosomes making up each pair are identical to each other
In females, the two sex chromosomes are also identical and are referred to as XX chromosomes
In males, on of these is an X chromosome and the other is a Y chromosome
Therefore, 44 + XX chromosomes (in females) and 44 + XY chromosomes (in males)
There are really two sets of 23 different kinds of chromosomes in each Somatic Cell, we say that the cells have a Diploid (2n) number of chromosomes (46)
Sex Cells or gametes of humans have just one set of 23 different chromosomes. The sex cells or gametes have a Haploid (n) number of chromosomes (23)

Question 3

What is meiosis

Answer 3

Meiosis is the division of one cell into four cells each of which has half the chromosome number as the parent cell. Furthermore, each of the four cells is genetically different from each other
Meiosis usually occurs during gametogenesis, a process during which gametes are formed
In plants meiosis occurs in the anther to produce pollen grains and in the ovary to produce the ovule
In humans meiosis occurs in the testes to produce sperms and in the ovary to produce an ovum
In some lower organisms, meiosis occurs immediately after fertilization