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Inherited sources of genetic variation.

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Introduction

Inherited sources of genetic variation One of the key features of all living things from single celled organisms such as amoeba, to plants and animals such as humans, is the ability to reproduce. In smaller single celled organisms such as the amoeba this reproduction is asexual and takes place by a process known as mitosis. Mitosis produces two daughter cells that are genetically identical to, or clones of their parent cell. This process however produces no genetic variation within a community; meaning that the process of evolution is limited and can only take place through an advantageous mutation over a long period of time. Mitosis also produces somatic, or body cells for growth and repair in multi-cellular organisms. To increase genetic variation other larger and more complex organisms such as plants and animals reproduce sexually by Meiosis. ...read more.

Middle

It is this random shuffling process that creates a huge variety of gametes from a single parent. Recombination occurs when pieces of chromosomes are exchanged within their homologous pair. This increases the swapping of genetic information leading to more genetic variation. Crossing over only occurs in the first division of meiosis, this is when whole groups of genes are mutually exchanged between the homologous chromosomes. The other factor allowing genetic variation to take place is mate selection. Variation is furthered by the ability of an individual to choose a mate with which to produce offspring. Different combinations of genes will come together in the offspring during fertilisation, depending on which two individuals mate. Mutations also cause variation, as they are the source of all new genetic information. Whilst most mutations are harmful, there are others that are described as 'silent' this means that these mutations have no known effect on the individual, and some can provide an improvement on the original version of the gene. ...read more.

Conclusion

This is caused by a point mutation which is located on the HBB gene on chromosome 11 and involves the substitution of one base for another this alters a single amino acid. This new amino acid makes the haemoglobin behave in a different manner as it has different properties. One other inherited disorder is Down syndrome, which is caused by Trisomy. This is when three chromosomes represent one chromosome pair. The mutation for Down syndrome occurs on chromosome 21, the most common form of this condition arises when meiosis fails to separate the pair of chromosome 21 in female ova. One in 800 babies born to mothers aged 30 to31 have Down syndrome, however this increases rapidly with the mothers age. Some of the symptoms include poor muscle tone, congenital heart disease and mental retardation. Jessica Jennings 13 Kee ...read more.

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