Selasa, 26 Jun 2012

Cell Division

All organisms go through the process of reproduction to produce offspring. Offspring always resemble their parents because they have inherited their parents characteristics such as the physical appearance (hair, skin colour, etc.) and biological aspects (intelligence, blood group, etc.). Heredity is the process where the characteristics of the parents are passed down to the offspring. The component in the cell responsible in heredity is the chromosome. A chromosome is made of DNA molecules and a small segment of the DNA molecules is called a gene.

In order to understand how these characteristics are passed down from parent to offspring, we have to look at the components of the cell responsible for such a process. The part inside the cell that is responsible for heredity is the chromosome. It is made of DNA and a small segment of the DNA is called a gene.
We need to understand how a cell divides and how chromosomes are carried from one cell to another. The two processes responsible are mitosis and meiosis.

Chromosomes, Deoxyribonucleic Acid (DNA) and Genes
In the nucleus of every cell, there are many fine thread-like structures called chromosomes. They carry genetic information. Thus, the unique characteristics that we possess are determined by information that is found in the chromosomes.

Chromosomes always exist in pairs except in the reproductive cells. The two chromosomes of a pair are called homologous chromosomes. Every living organism has a specific (fixed) number of chromosomes in its body cells. The table below shows the number of chromosomes in the cells of some organisms.

Various organisms and number of chromosomes in their somatic cells

Chromosomes are made up of deoxyribonucleic acid (DNA). The structure of a DNA molecule is very complicated. Each DNA molecule has two strands which coil around each other to form a double helix. A gene is a small section in the DNA and each DNA molecule contains thousands of genes


Genes are also known as units of inheritance as the inherited characteristics are passed from parents to offsprings through the genes in the sperms and ova. Genes present themselves in pairs. One is inherited from the father and the other is from the mother. Each chromosome contains thousands of different genes. For example, there is a type of gene that controls our hair colour and another gene that controls eye colour.

The structure of a chromosome and the DNA molecule is shown below.

Structure of a chromosome and DNA molecule
Cell Division

Cell division is responsible for growth and reproduction. After growing to a certain size, the cell reproduces by cell division and the cells can become multicellular. One has to understand the process of cell division in order to understand how genes are inherited. There are two types of cell division, namely:
i. Mitosis
ii. Meiosis

#mitosis and meiosis
#Different between mitosis and meiosis

prepared by : kasturi

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