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The Causes and Importance of Variation and Diversity in Organisms
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The Causes and Importance of Variation and Diversity in Organisms full essay. Word count 1009, mark = 18/25
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The Causes and Importance of Variation and Diversity in OrganismsIn organisms, variation and diversity are very important. Variation is the difference in genetic
make-up between individuals within a species, and diversity is the number of different species in
a community. Genetic diversity is the number of different alleles in a population. These are
important for the survival of organisms, and are caused by a number of factors, including
meiosis and gene mutation.
One cause of variation and diversity in organisms is meiosis. During this process, one cell
divides twice to produce four genetically different haploid cells. These daughter cells contain a
different combination of genetic information, which is achieved partly through independent
segregation of homologous chromosomes. In meiosis, homologous pairs of chromosomes line
up randomly - in humans, this is 23 pairs. These pairs of chromosomes then split and pass to
each daughter cell, which is also random. Because of this, the combination of maternal and
paternal chromosomes in each cell is a matter of chance. This creates new genetic
combinations and, due to the differing alleles that each chromosome has, creates new allele
combinations, therefore increasing variation in organisms. Variation through meiosis is also
achieved through crossing over. When homologous chromosomes line up, the chromatids of
each pair twist around each other and this creates tension, causing portions of the chromatid to
break off. These broken portions then rejoin with the other chromatid, meaning equivalent
portions of homologous chromosomes are exchanged. This produces new genetic
combinations, and increases the variation of alleles in organisms. Therefore, meiosis, and both
these processes, are causes of variation, and are important for this as it allows new genetic
combinations which could be advantageous and lead to adaptation or natural selection.
Another cause of variation and diversity in organisms is gene mutation. A gene is a section of
DNA that codes for a polypeptide, and a mutation is a change in the base sequence of the
gene, or the quantity of DNA. Base sequence mutations can be carried out by deletion, insertion
or substitution of bases, and if they are germline, they are passed onto offspring. Base
sequence mutations can code for new amino acids, resulting in different proteins being
produced. For example, the triplet CAT codes for the amino acid His, but a base substitution
resulting in the triplet CGT would result in the amino acid Arg being coded for. This could result
in someone having green eyes instead of blue. Other mutations could cause different leaf sizes,
or root length. Because of mutations in the DNA, other genotypes and phenotypes are created,
This then increases the variation in species, as new proteins are coded for by genes, and
diversity, as it can increase the number of alleles in a population. This can also lead to
processes such as natural selection and adaptation.
Natural selection is an evolutionary process that results in the survival of the better adapted
individuals of a species. When a random mutation occurs in a gene pool that results in an
advantageous allele or gene being coded for, individuals possessing this are more likely to
successfully survive and reproduce because they are better adapted. Their offspring, which also
have this advantageous gene, are also more likely to survive than other individuals. Over many
generations, those with the advantage increase in numbers, whilst those without it decrease and
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