Inheritance Definitions

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  • Created by: ava.scott
  • Created on: 28-01-15 10:30
The study of mechanisms by which an organism inherits characteristics from its parents.
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one of the different forms of gene
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A section of DNA on a chromosome that codes for a particular polypeptide
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different alleles at equivalent loci
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same alleles at equivalent loci
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monohybrid inheritance
The inheritance of a single characteristic by a single gene.
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Test/Back cross
Use to determine whether an individual in homozygous dominant or heterozygous. Breed with a individual who is definitely homozygous recessive.
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Dihybrid inheritance
Involves the inheritance of two separate genes, e.g. wrinkled/smooth and green/yellow
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Mendel's first law
Characteristics are defined by allles that come in pairs. Only one of the pair of alleles can be found in a gamete.
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Mendel's second law
Each member of an allelic pair may combine randomly with either of another pair.
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Rule of addition
The probability of getting a result can be added to the probability of getting all the other results, to get 100%
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Rule of multiplication
To get the probability of getting both results, you multiply their probability together.
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Used to measure significance of the results in a experiment. Calculated probability of deviation must be larger that 95%.
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Chi2 table
Phenotype, Observed result, expected result, observed-expected, (o-e)^2, (o-e)^2/E
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Degrees of freedom
One less than the number of classes in the table. 4 classes= 3 degree of freedom.
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When both alleles are dominant and are expressed equally in the phenotype.
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Co-dominance 2
The heterozygous dominant individual will have a different phenotype to both homozygous parents.
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Incomplete dominance
The phenotype is a blend of the two dominant homozygotes.
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Sex determination
Determined by X and Y genes in humans
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Sex linked
When alleles are found on the sex chromosomes. They are usually inherited together.
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Recessive allele ofn the X chromosome. Men don't have an additional X chromosome, so the recessive one is the only gene that is expressed. Women need to be homozygous recessive to get it.
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An individual with one normal allele and one potentially harmful allele. They have a 'normal' phenotype.
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When two different genes are found on the same chromosome and are generally inherited together. They do NOT follow typical mendelian pattern.
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When crossing over takes place between linked genes.
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change in the amount, arrangement or structure in the DNA of an organism.
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Two types of mutation
Gene and chromosonal
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chroomosomal mutation
e.g. Down syndorme. effects whole number of chromosomes in DNA
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Gene mutations
e.g. sickle cell anaemia, one gene is affected and mutated so it doesn't function properly
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a faulty cell division where one of the cells recieves two copies of a chromoskme, when the other gets none.
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an increase in the number of complete sets of chromosomes
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What can mutation lead to?
They are random events, but can lead to selective advantage and a material for selection pressures and evolution.
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Mutation rates are...
Low, the shorter the life cycle, and the more frequent meiosis is, the higher the rate of mutation.
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increase rate of utation e.g. ionising radition, UV, X-ray and chemicals
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Chemical mutagens
polycylic hydrocarbons in cigarette smoke.
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mutagen that cases cancerous mutations
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How does mutation cause change in phenotype?
Muattion leads to a change in base sequence, which can cause a different amino acid to be chosen in the primary sequence of a protein. This changes its function, stopping a molecular process, and therefore affecting the phenotype.
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a mutated gene that cause cancer, by letting cells divide uncontrollably.
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example sof the oncogenes
proto-oncogenes (stimulate cell division) and tumour suppressor genes (slow down cell division)
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Card 2


one of the different forms of gene



Card 3


A section of DNA on a chromosome that codes for a particular polypeptide


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Card 4


different alleles at equivalent loci


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Card 5


same alleles at equivalent loci


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