Genetics
- Created by: Dominic Hayward
- Created on: 01-11-13 13:55
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- Genetics
- DNA
- contains all the genetic information.
- Has a double helix structure-2 strands coiled around each other. Strands of polynucleotides joined in a long chain.
- A nucleotide is made from a phosphate group, a pentose sugar (with 5 carbon atoms) and a nitrogenous base. The base can vary.
- Four bases: Adenine, Thymine, Cytosine and Guanine.
- Specific base pairing occurs (Adenine can only join with Thymine) and (Cytosine and Guanine).
- Adenine and Thymine join with 2 hydrogen bonds and Cytosine and Guanine join with 3 hydrogen bonds.
- Specific base pairing occurs (Adenine can only join with Thymine) and (Cytosine and Guanine).
- Four bases: Adenine, Thymine, Cytosine and Guanine.
- The double helix structure prevents damage from occurring.
- It is also coiled which allows more DNA to be stored.
- It has a paired structure which makes it easier to copy itself.
- It is also coiled which allows more DNA to be stored.
- Eukaryotic and Prokaryotic Cells
- Prokaryotic cells have DNA that is supercoiled.
- Eukaryotic cells is linear DNA that exists in chromosomes. It wraps around proteins called histones that support the DNA.
- Genes
- Genes are sections of DNA.
- Proteins are made from amino acids. The order of nucleotide bases that determines the order of amino acids.
- Each amino acid is coded for by three bases ( a triplet code)
- DNA is degenerative as more than one triplet codes for the same amino acid. There are 64 triplets and only 20 amino acids.
- Pairs of matching chromosomes are called homologous pairs. They have the same shape and genes, but could have different alleles.
- Meiosis and Genetic Variation
- Gametes are sex cells; sperm and eggs.
- Normal body cells have the diploid number but gametes have the haploid number.
- Meiosis is a type of cell division that creates gametes with the haploid.
- A cell with the diploid number replicates to form a cell with chromatids
- Then the chromosomes arrange into homologous pairs
- The first division occurs where the homologous pairs are separated.
- The second cell division occurs where the sister chromosomes are separated.
- The first division occurs where the homologous pairs are separated.
- Then the chromosomes arrange into homologous pairs
- A cell with the diploid number replicates to form a cell with chromatids
- Crossing over occurs when the homologous pairs come together. Parts of chromosomes touch and break off and join a different chromosome creating a new chromosome with different alleles.
- Because the alleles have changed it causes variation as it is different to all other chromosomes.
- The chromosomes can break in any order so the homologous pairs can go with any other chromosome. This process is random so variation is created.
- Genetic Diversity
- Genetic diversity is the amount of alleles in a population. It is important as it allows the species to survive diseases.
- Mutations and gene flow both increase genetic diversity
- Genetic diversity is reduced when a natural disaster or a disease wipes out a lot of the population. The number of alleles is reduced.
- It is also reduced when part of the population moves to a new area. The population in the new area all have alleles from the founders.
- Selective breeding also reduces the alleles in a population as undesired characteristics are breed out of the population.
- Argument for and against selective breeding
- For:
- Increased resistance to disease.
- Creates high yeilds
- Increased tolerance to bad conditions.
- Against:
- Reduces genetic diversity
- Causes health problems
- For:
- DNA
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