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Biology Topic 6 Inheritance, Variation and Evolution - Coggle Diagram
Biology Topic 6 Inheritance, Variation and Evolution
DNA
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DNA is found in the nucleus of animal and plant cells, in chromosomes
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Genes
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DNA determines which protein is made (e.g. haemoglobin) and in turn determines which type of cell (e.g. red blood cell)
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Structure of DNA
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each nucleotide consists of a sugar, phosphate group and one base
the sugar and phosphate group form a backbone and they alternate. One of four bases A,T,C or G join to each sugar
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Mutations
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mutations occur continuously and can occur spontaneously but they can also be influenced by certain substances or some types of radiation
mutations change the sequence of DNA bases which can produce a genetic variant. since DNA bases code for the amino acids that make proteins, mutations can lead to changes in the protein made
most mutations have very little or no effect on the protein but some can seriously affect a protein (e.g. if the shape of the enzymes active site is changed the substrate will no longer fit
Types of Mutations
1. Insertions
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every three bases code for a particular amino acid so adding one can have a knock on effect to the sequence
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2. Deletions
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like insertions, this then has a knock on effect to the sequence
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Functions of Proteins
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2.Hormones- used to carry messages around the body e.g. insulin is released into the blood by the pancreas to regulate blood sugar level
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Reproduction
Sexual Reproduction
genetic information from two organisms (a father and a mother) are combined to produce offspring which are genetically different to either parent
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in humans, each gamete contains 23 chromosomes which is half the number of chromosomes in a normal cell
the egg and the sperm cell then fuse together (fertilisation) to form a cell with a full set of chromosomes
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Asexual Reproduction
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bacteria, some plants and some animals asexually reproduce
Meiosis
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before the cell divides, it duplicates it's genetic information
in the first division, the chromosome pairs line up in the centre of the cell
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in the second division, the chromosomes line up again and the arms of the chromosomes are pulled apart
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finally the new cells divide by mitosis to make a copy of itself. Mitosis repeats many times to produce lots of new embryo
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X and Y chromosomes
there are 22 pairs of matching chromosomes in the human body and the last pair is labelled XX or XY. These chromosomes determine your sex.
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when making eggs the original cell has two X-chromosomes, so all the eggs have one X chromosome
Inherited disorders
Cystic Fibrosis
a genetic disorder of the cell membranes that results in the body producing a lot of thick sticky mucus in the air passages and pancreas
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because it's recessive, people with only one allele won't have the disorder but are known as carriers
for a child to get the disorder both parents must either be carriers or have the disorder themselves
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Polydactyly
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the allele that causes it is dominant 'D' so it can be inherited if just one parent carries the defective allele
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Embryonic Screening
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many genetic disorders can be identified this way however there are many ethical, social and economic concerns
For: it will stop people suffering, treating disorders costs the government and taxpayers a lot of money, there are laws to stop it going too far
Against: implies people with genetic problems are 'undesirable', it may go too far where everybody wants the most 'desirable' child, screening is expensive
The Work of Mendel
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Conclusions: 1. characteristics in plants are determined by hereditary units. 2. hereditary units are passed on to offspring unchanged from both parents. 3. hereditary units can be dominant or recessive
Variation
organisms within the same species have differences and this can be down to environmental or genetic variation
Genetic Variation all plants and animals gain characteristics from their parents and majority of animals and plants get some form each parent. Combining the genes causes genetic variation as no two of the species are the same. Some characteristics are only determined by genes: eye colour, blood group, inherited disorders
Environmental variation the environment, including conditions that an organism lives and grows in causes differences within species. For example, a plant living in sunlight will be green but if the same plant was grown in darkness it would turn yellow.
Evolution
THEORY OF EVOLUTION all of today's species have evolved from simple life forms that first started to develop over three billion years ago
Charles Darwin knew that organisms in a species show wide variation in their characteristics and that they have to compete for limited resources. Darwin concluded that organisms with the most suitable characteristics for the environment would be the most successful competitors and are more likely to survive. This is called 'survival of the fittest'.
He also said that these successful organisms are more likely to reproduce and pass on the genes to the offspring. Overtime more beneficial characteristics become more common in the population and the species evolves.
Over a long period of time the phenotype of organisms can change so much because of natural selection that a completely new species is formed. This is called speciation.
Speciation
Isolation is where populations of a species are seperated. This can happen due to a physical barrier e.g. floods and earthquakes cause barriers that geographically isolate. Conditions on either side will be different so different characteristics will become more common in each population.
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Alfred Russel Wallace was a scientist working at the same time of Charles Darwin and worked on speciation. Wallace independently came up with the idea of natural selection and published work with Darwin in 1858. He identified that warning colours are used by some species (e.g. butterflies use them to deter predators) which is a beneficial characteristic.
Extinction
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- the environment changes too quickly
- a new predator kills them all
- a new disease kills them all
- they can't compete with a new species for food
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Lamarck argued that a characteristic an organism acquires during its lifetime will be passed on to its offspring. For example if a rabbit used its legs a lot to escape predators, its offspring will be born with longer legs.
However this idea was rejected because if you have your arm amputated then your offspring still has arms. This being rejected helped support Darwin's theory.
Selective Breeding
When humans artificially select the plants or animals that are going to breed so that the genes for a particular characteristic remains in the population.
This may be done to produce more meat or milk, make crops disease resistant, have dogs with a gentle temperament and have decorative plants with big flowers.
The main drawback is a reduction of gene pool. the number of different alleles in a population is decreased because the farmer keeps choosing the 'best' animals or plants which is called inbreeding
Inbreeding can cause health problems because there is a higher chance of inheriting harmful genetic defects. Dogs are particularly susceptible to defects e.g. pugs have breathing problems
Genetic Engineering
- A useful gene is cut from one organism's genome using enzymes and is inserted into a vector.
- The vector is usually a virus or a bacterial plasmid depending on the type of organism the gene is being transferred to.
- The useful gene is inserted into the cell.
This can be used for things like: modifying bacteria to produce human insulin to treat diabetes, genetically modified crops to produce a better yield
Pros of GM crops: increase the yield, engineer crops to have the nutrients that people in developing countries need, majority of the time there is no problems
Cons of GM crops: affects the number of wild flowers which affects the population of insects, can impact human health, weeds may pick up the transplanted genes which would create a 'superweed'
Cloning
Tissue Culture
this is where a few plant cells are put in a growth medium with hormones and they grow into new plants- clones of the parent plant. These plants can be grown very quickly, in very little space and all year round. These are used by scientists to preserve rare plants.
Cuttings
Gardeners can take cuttings from good parents plants and then plant them to produce genetically identical copies. These plants can be produced quickly, cheaply and is an older simpler method.
Animal Clones
Sperm and egg cells are taken from a prize animal and the sperm then artificially fertilities the egg. These cloned embryos can then be implanted into lots of this organism and hundreds of a prize animal is made.
Adult cell cloning involves taking an unfertilised egg cell and removing its nucleus. The nucleus is then removed from an adult body cell and is insterted into an 'empty' egg cell. The egg cell is then simulated to divide by an electric shock and this can be implanted into the womb of an adult female. It grows into a clone.
Issues surrounding cloning: reduced gene pool, clones are not as healthy, may lead to human cloning
Fossils
1.Gradual Replacement by minerals Things like teeth, shells and bones which don't decay easily last for a long time. They're eventually replaced by minerals and form a rock-like substance. The sediments surrounding it also turn to rock but the fossil stays distinct.
2. Casts and Impressions Sometimes fossils are formed when an organism is buried in soft material like clay. The clay hardens and the organism decays which leaves a cast of itself.
3. Preservation in Places Where No Decay Happens in amber and tar pits there's no oxygen or moisture so decay microbes can't survive. in glaciers its too cold for decay microbes to work. Peat bogs are too acidic for decay microbes. A fully preserved man they named 'Pete Marsh' was found in a bog.
Classification
First proposed by Carl Linnaeus that organisms should be classified according to characteristics and structures. Firstly, living things are divided into kingdoms and then into smaller groups- phylum, class, order, family, genus, species.
Since knowledge of the biochemical processes have improved due to things like microscopes new models of classification have been put forward.
Carl Woese proposed the three-domain system which consisted of the Archaea where organisms were once thought to be primitive bacteria but they're actually prokaryotic. There was also Bacteria which contains true bacteria like E.coli. Finally there was Eukaryota which includes a broad range of organisms like fungi, animals, plants and protists.
These are then subdivided into smaller groups- kingdom, phylum, class, order, family, genus and species
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