In order to understand cell division it’s important to know first of all how genetic material is composed.

DNA

DNA, short for deoxyribose nucleic acid, is very large molecules which carry the genetic code: this is what determines the characteristics for every organism. Apart from identical twins, every human being has DNA which is unique to them only.

Genes

A gene is the coding for a protein. It’s made up of a small sequence, or segment, of DNA.

Chromosomes

A chromosome is a complete length of DNA molecules. Chromosomes are normally found in pairs within cell nucleus so that each nucleus has two sets.

Nucleus

This is where the genetic information is stored in animals and plants.

Mitosis

All cells in the body divide by a process known as mitosis. When a cell divides in this way:

• the genetic material is replicated
• two genetically identical body cells are formed

There are two main purposes for mitosis:

• growth
• to create replacement cells

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Alleles

Sexual reproduction produces offspring that are different from either parent. This is because the gametes of each parent contain half the genetic material required.

Genetic information is made up of genes and each pair of chromosomes carries the same genes. However, sometimes there are different versions of the same gene available, for example eye and hair colour, and these different versions are called alleles.

Alleles can be either recessive or dominant:

• A recessive allele is only able to show itself as a characteristic if there are two copies of it. In other words, if the allele is present on both chromosomes. For example, blond hair is a recessive allele.
• A dominant gene will always show its characteristic, whether it’s present on one or two chromosomes. Brown hair is a dominant allele.

The variations seen through sexual reproduction is due to the different alleles received from the each parent.

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Differentiation

In animals the cells tend to differentiate at an early stage of development. As an animal matures cell division becomes solely focused on repair and replacement. In many plants, however, the ability to differentiate cells continues throughout its lifetime.

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Stem cells

Stem cells are undifferentiated cells which have the ability to differentiate into specialised cells. They can be found in two main sources:

• adult bone marrow
• embryos

They can be made to differentiate into any kind of human cell, like a nerve cell.

NOTE: You don’t need to know of any stem cell techniques.

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Stem cell treatment

Due to their properties, stem cells can be used to treat a number of conditions, including:

• paralysis
• brain diseases like Alzheimer’s
• skin tissue for burn victims

There are a number of social and ethical concerns regarding the use of embryo stem cells. The main argument is that by destroying an embryo you’re destroying human life.