B1.7 Reproduction Cloning and Genetic Enginering

Inheriting DNA

The information that results in plants and animals having similar characteristics to their parents is carried by genes, which are passed on in the sex cells (gametes) from which the offspring inherit.

The gametes join and fuse together furing fertilisation. Fertilised eggs have two sets of genes, which will control the development of characteristics we inherit.

Genes are linked together in long thread-like structures called DNA. It is made from two strands, which are twisted together to make a spiral. This is called a double helix.

The nucleas of a cell normally has two sets of chromosomes in it. Genes and chromosomes are made from a chemical called DNA. We obtain one set from our mothers egg and the other from our fathers sperm. Humans have 48 chromosomes in each nucleas so each set has 23 chromosomes.

Causes of Variation

Difference in the characteristics of any different individuals of the same species may be due to a range of factors.

Environmental and inherited characteristics

Some characteristics of an individual are caused by the enviroment. For example, the language we use or whether we have scars are known as enviromental characteristics.

Here are some inherited characteristics:

• The shape of the earlobes
• Eye colour
• Nose shape

Some characteristic - including intelligence, body mass and height - are a result of both enviromental and inherited factors.

Genotype - The full set of genes of an organism
Phenotype - the observable characteristics of an organism

Asexual Reproduction

Asexual Reproduction only involves one parent. it is very common in smaller animals and bacteria, although it does occur in larger plants such as daffidils or strawberries. Bulbs, corns or tubas are all ways in which plants can reproduce asexually.

During asexual reproduction there is no joining of sex cells. The offspring contain identical genetical information to their parents. The offspring therefore do not show variation. All offspring are identical to each other and to their parents. Such identical offsring are called clones.

Sexual Reproduction

This process involves the fusion of a male sex cell (sperm in animals) with a female sex cell (egg) from two different parents. These two special cells or gametes will join to form a new individual. The gametes only contain half the number of chromosomes found in a normal body cell. They have one of each type of chromosome not two of each type as found in body cells.

At fertilisation, when the sperm and egg fuse, a fertilised cell or zygote is produced with the full number of chromosomes (half from the egg and half from the sperm). hence the new individual will show some of the same characteristics of each parent as it has recieved a mixture of chromosomes from both parents. This introduces variation. Variation in a species is very important for its survival. The more variety in a population, the more likely it is that some individuals will survive different conditions; if they were all identical they could all be killed.

It is more risky…