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Inheritance, variation and evolution (Genetic inheritance (Gene: a section…
Inheritance, variation and evolution
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Meiois
halves the number of chromosomes in gametes and fertilisation restores the full number of chromosome
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Gametes join at fertilisation to restore the normal number of chromosomes. The new cell divides by mitosis. The number of cells increases. As the embryo develops cells differentiate
DNA and the genome
the genetic material in the nucleus of a cell is composed of a chemical called DNA. DNA is a polymer made up of two strand forming a double helix. The DNA is contained in structures called chromosomes.
a gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, to make a specific protein
the genome of an organism is the entire genetic material of that organism. The whole human genome has now been studied and this will have great importance for medicine in the future
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Inherited disorders
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Embryonic screening
Advantages
- it will help to stop people suffering
- treating disorders costs the Government a lot of money
- there are laws to stop it going too far.
Disadvantages
- it implies that people with genetic disorders are 'undesirable - this could increase prdjudice
- there may come a point where everyone wants to screen their embryos so they can pick the most 'desirable' one
- screening is expensive
Resistant bacteria
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Mutation of bacterial pathogens produce new strains. Some strains might be resistant to antibiotics, and so are not killed. They survive and reproduce , so population of the resistant strain rises. The resistant strain will then spread because people are not immune to it and there is no effective treatment
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Evolution: a change in the inherited characteristic of a population over time through a process of natural selection which may result in the formation of a new species
The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago
evolution occurs through natural selection of variants that give rise to phenotypes best suited to their environment
if two populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring they have formed two new species
Selective breeding: the process by which humans breed plants and animals for particular genetic characteristics
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Genetic engineering: a process which involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic
genes from the chromosome of humans and other organisms an be 'cut out' and transferred to cells of other organisms
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- enzymes are used to isolate the required gene; this gene is inserted into a veto, usually a bacterial plasmid or a virus
- the vector is used to insert the gene into the required cells
- genes are transferred to the cells of animals. plants or microorganisms at an early stage in their development so that they develop with desired characteristics
Evidence for evolution
Evidence for Darwin's theory is now available as it as been shown that characteristics are passed on to offspring in genes. There is now further evidence in the fossil record and the knowledge of how resistance to antibiotics evolves in bacteria
Genetic inheritance
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most characteristics are a result of multiple genes interacting, rather than a single gene
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Sex determination
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22 pairs control characteristics only, but one of the pairs carries the genes that determined sex
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