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 their parents, but are not identical to them.
Offspring resemble their parents because they contain genetic information passed on to them by their parents.
Chromosomes and genes
Chromosomes, found 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 for a whole organism.
The number of genes and chromosomes varies from species to species. For example, cells in human beings have 46 chromosomes that carry about 30,000 genes in each cell; and cells in fruit flies have 8 chromosomes that carry about 13,600 genes.
Although individuals of a species look similar, they are not usually identical: these differences are called variation.
Variation due to genetic causes is inherited variation. For example, children usually look a little like their father, and a little like their mother, but they will not be identical to either of their parents. This is because they get half of their inherited features from each parent.
Here are some examples of inherited variation in humans:
- eye colour
- hair colour
- skin colour.
Some variation within a species is inherited, and some variation is due to the environment; some variation is due to a combination of both.
Characteristics of animal and plant species can be affected by factors such as:
For example, if you eat too much you will become heavier, and if you eat too little you will become lighter. A plant in the shade of a big tree will grow taller as it tries to reach more light.
Variation caused by the conditions is called environmental variation. Here are some other examples of features that show environmental variation:
- your language
- your religion
- flower colour in hydrangeas (as these plants produce blue flowers in acidic soil and pink flowers in alkaline soil).
Combined genetic and environmental factors
Some features vary because of a combination of genetic causes and environmental causes. For example, identical twins inherit exactly the same genetic information from their parents. But if you take a pair of twins, and twin A is given more to eat than twin B, twin A is likely to end up heavier.
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 cloned using embryo transplants or fusion cell cloning. Genetic information from one species can be transferred to another species using genetic…