The causes and importance of variation and diversity of organisms PDF

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The causes and importance of variation and diversity of organisms Maintaining genetic diversity is of vital importance to all species so they can continue to evolve and adapt to their ever changing environmental conditions. It also reduces the risk of mutations occurring, helping decrease the risk of life threatening disorders being inherited by the next generation. The causes of diversity are varied. One way that genetic diversity comes about is meiosis. During meiosis 1 chromosomes become visible during prophase, homologous chromosomes pair up and line up along the equator of the cell in metaphase. During this stage non-sister chromatids can undergo crossing over. Sections of the chromatids are broken off and transferred to the other chromosome. This increases genetic diversity as chromosomes can interchange different genes so that they are genetically different to their parents. This is vital as, as the offspring are genetically different to the parents, it reduces the chance of inbreeding which can increase the likelihood of mutations occurring (which can lead to disorders). Spindles fibres during anaphase join to the chromosomes, contract, pulling the homologous chromosomes to opposite ends of the cell. So that during cytokinesis the cell divides producing daughter cells. Furthermore, meiosis 2 further increases genetic diversity. Chromosomes undergo the same stages as in meiosis 1 (but there’s no homologous chromosomes this time). So that during anaphase, spindle fibres bind to the chromosomes centromere, contract, pulling two sister chromatids to opposite poles of the cell. This further increases genetic diversity as during cytokinesis here, 4 daughter cells are produced which are all genetically different. The importance of this to organisms is that, as fertilisation is random, this creates different combinations of paternal and maternal chromosomes meaning that all of the offspring are slightly genetically different. Helping to maintain the size of the gene pool as a lack of genetic diversity can increase the chance of mutations. Mutations are another way diversity is caused. Mutations can occur due to many things, High ionising radiation and chemicals can all affect the primary base sequence in an organism's DNA. This leads to a frameshift in this sequence. This consequentially could mean that a gene is activated which codes for a protein that gives this individual resistance to a disease (for example malaria). This example is known is known as sickle cell anemia.If this individual reproduces, its offspring are likely to inherit the allele, which gives it resistance to malaria. Therefore mutations are crucial to maintaining populations as they can provide resistance to diseases that stop the whole species being wiped out (stops genetic bottlenecks wiping out whole species). Variation, as well as genetically is of vital importance as it provides intraspecific and interspecific variation. Interspecific variation is the variation between species. This can come about due to environmental causes. Geographical isolation for instance may separate a species from each other. As there is no gene flow between the gene pools (separated physically, for example by water- due to plates separating) they start to evolve separately. For example, if an individual on an island has a recessive allele that allows it to be better camouflage from predators, this individual is less likely to be eaten than than non recessive allele individuals. Meaning after a couple of generations (during which reproduction occurs) this recessive allele

may become the dominant allele on the Islands. Creating a species that looks different to the species it was separated from. This process describes natural selection. Different selectional pressures (in this instance predation; as well as climate, food availability etc) in different areas of an enviroment mean that over generations, individuals with favourable alleles, these alleles start to become dominant; helping the species to adapt to it’s environment, which in the process can lead to speciation if there is no gene flow. Interspecific variation (from allopatric speciation) means that, as species have been so separated physically for so long, the cannot mate and produce fertile offspring together. This is important as most species rely on species specific visual stimuli. Variation between species means that, as mating rituals are normally varied between species, organisms of the same species can work out a mate from their own species so they can mate to produce fertile offspring. If there was limited phenotypic variation between species this would increase the chance of individuals from different species reproducing and producing infertile offspring which would dramatically reduce population sizes and probably would lead to extinction. At a molecular level, variation in proteins is of vital importance. Proteins can form many molecular structures. This is because, although there is a universal code (nearly all organisms have bases A,T, G, C and U) the triplets code for one amino acid during translation. This is vital as the types of amino acid determine the primary amino acid structure, which determines the protein's tertiary structure. If for example the protein is an enzyme the tertiary structure determines the shape of the active site. Therefore variation in the genetic code is needed so specific proteins can be transcribed. Crucial as enzymes, such as proteases need to have a specific tertiary structure so that it’s active site is complementary to a protein so that an E-S complex can be formed and the substrate is broken down (allowing for easier absorption into cells). Antibody variation is also important for the bodies immune system. It allows antibodies to be produced that are specific for the different types of antigens found on pathogens. During the primary immune response, B-lymphocytes take up the pathogens antigens and with the help of T helper cells secrete specific antibodies. These antibodies have a specific, complementary binding site to only one antigen, so they can bind, causing agglutination so cytotoxic T-cells can more easily destroy the antigen, Thus variation in proteins tertiary structure (produced by the primary immune response) is vital for the immune response...