Continuity and Variation

Chapter 15: Continuity and Variation

• Chromosomes are made of Deoxyribonucleic Acid and Protein, and are present in the nuclei of cells. In non-dividing cells, they are long thin strands called chromatin threads. During cell division, the chromosomes shorten, thicken and become visible.
• Chromosomes have genetic information as Genes.
• In Humans, every body cell has 46 chromosomes which are homologous pairs, 23 of maternal origin and 23 of paternal origin. Chromosomes are passed on in gametes.
• Genes are the basic unit of hereditary. They control the structure and functioning of cells by controlling proteins (enzyme) production. They control the characteristics of organisms.

Cell Division

• In cell Division, Chromosomes and their genes are passed on to daughter cells. There are 2 types of ell division: Mitosis & Meiosis.

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Cell Division cont'd: Mitosis

• This occurs in all body cells except gametes. Mitosis results in the formation of two genetically identical cells, each containing the same number of chromosomes as the parent cell, Diploid or 2n number.