Biology: Genetic variation and its control

Why organisms are different

The genetic information passed from parent to offspring is contained in genes carried by chromosomes in the nucleus. Sexual reproduction produces offspring that resemble the parent but are not identical to them.

Offspring resemble their parents because they contain genetic information passed on to them from their parents. 

Chromosomes in the cell nucleus contain many genes. A gene is a section of DNA which carries coding for a particular protein. Different genes control the development of different characteristics of an organism. Many genes are needed to carry all the genetic information need for a whole organism. 

Cells in humans have 46 chromosomes that carry around 30,000 genes in each cell. This number varies from species to species. 

Variation due to genetic causes in an inherited variation. Examples of inherited variation include: eye colour, hair colour and skin colour. 

Some variation within a species in inherited and some variation is due to the environment. Some is a combination of both. 

Characteristics of animals and plant species can be affected by factors such as: climate, diet, accidents, culture and lifestyle. For example, if you eat too much, you will become heavier. A plant in the shade of a big tree with grow taller as it tries to reach more light. 

Variation caused by the conditions is an environmental variation. Some other examples of features that show environmental variation include: language, religion and flower colours in hydrangeas. 

Some features vary because of a combination of genetic and environmental causes. For example, identical twins inherit exactly the same genetic information from their parents but if you give twin A more food than twin B, it will become heavier. 

Reproduction

Sexual reproduction produces offspring that resemble their parents but are not identical to them. Asexual reproduction produces offspring, clones, which are genetically identical to their parents. Plants can be cloned artificially using cuttings or tissue culture. Animals can be used using embryo transplants or fusion cell cloning. Genetic information from one species can be transferred to another species using genetic modification. 

Organisms have sex cells called gametes. In human beings, the male sex cells are sperm and the female sex cells are called eggs or ova. 

Sexual reproduction happens when a male gamete and female gamete join, this is called fertilisation. Sexual reproduction allows some of the genetic information from each parent to mix, producing offspring that resemble the parents…