Variation, Sexual and Asexual Reproduction

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The information that results in plants and animals having similar characteristics to their parents is carried by .

The genes are passed on in the sex cells, called . Different genes control the development of different .

The of every cell contains chromosomes. Inside the nucleus of a human body cell there are pairs of chromosomes. 23 chromosomes are provided by the , and 23 chromosomes are provided by the mother. Each chromosome contain long strands of , containing genes. There are thousands of genes within each chromosome. Every characteristic is controlled by genes. The mixture of genes will result in a child having some characteristics of their mother, and some of their father. Human reproduction is an example of reproduction

For every characteristic, there is a of genes. Many diseases are caused by faulty genes. Offspring are less likely to have genetic diseases if the are genetically very different. The healthy gene is usually dominant, and no disease is present in the offspring, even if a faulty gene is passed on by one of the . However, in some genetic diseases the faulty gene passed on by one of the parents can be dominant, and override the gene. Then the offspring will develop a genetic disease.

in individuals is caused by the different mixture of genes passes on by their parents. This is normally a good thing. The individuals with the best characteristics in a given will be the individuals most likely to survive, and pass on their charateristics to offspring

There are two types of reproduction, sexual and asexual reproduction.

Only one parent is needed in reproduction. In asexual reproduction the genes of the offspring are identical to the parent. These individuals are called .

There are different cloning that can be used

Cuttings (from plants) - The simplest way to a plant is to cut off part of a plant. The part can then be placed in moist soil or compost after dipping it into a growth

Tissue culture - Another way is to scrape off a few from a plant and place them in solution. The agar solution will contain nutrients for growth. The new plants are genetically to the parent plant.

Embryo transpant - In this procedure an is split up in its very early stages of development. For example, an 8 cell embryo can be divided into separate 2 cell embyos, by splitting. Each of the four embryos can then be placed in a surrogate . All the offspring will be genetically identical.

Fusion cell and adult cell cloning. - This is the procedure used to clone the sheep in 1996. In this procedure a body cell is removed from a sheep A to be cloned. The is removed . This will contain all the dna and genes for dolly. This is then fused inside an empty cell taken from another sheep B. The fused cell is then placed into a surrogate sheep C . The resulting lamb will be a of sheep A