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| The genetic composition of an organism |
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| Change of DNA (Mutation) can be inherited if it occurs in the formation of gametes |
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| Observable characteristics of an organism results from the expression of the genotype and it's interaction with the environment |
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| A section of DNA that is a sequence of nucleotide bases that usually determines a single charecteristic of an organism e.g eye colour by coding for specific polypeptides |
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CHANGE IS PHENOTYPE THAT DOESN'T EFFECT THE GENOTYPE AND ISN'T INHERITED |
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| Usuallt in two or more forms, called alleles. The position of a gene on a chromosome is called the locus |
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| Different forms of a gene |
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| Only one allele of a gene can occur at the locusof any one chromosome. |
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| Sexually reproducing organisms - the chromosomes occur in pairs. Two loci that can each carry one allele. |
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| Both loci have the same allele then the organism is said to be homozygous for the character. |
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| If the two alleles on the loci are different, then they are said to be heterozygous for that character |
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| In most cases where two alleles are present in the genotype, only one shows up in the phenotype |
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The allele of the heterozygote that expresses itself in the phenotype
Dominant alleles are always expressed in the phenotype |
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Only expressed in the phenotype in the presence of another identical recessive allele
They won't be expressed in heterozygous phenotypes |
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| Effect of recessive allele only expressed in diploid organisms - diploid: cells that contain two sets of chromosomes |
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| Two alleles both contribute to the phenotype. e.g a blend of both features |
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A gene has more than two allelic forms. However because there are only two chromosomes, only two of the multiple alleles can be part of a single organism.
e.g blood group ABO |
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| Inheritence of a single gene |
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Organisms with certian alleles bred repeatedly together so they give a rise of the organism with this characteristic.
So they have two alleles that are the same |
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| F1 generation - two pure breeding parent (one dominant and one recessive) organisms are bred together to form offspring with a dominant allele and with the recessive allele. The characteristics expressed will be that of the dominant allele |
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Term
WHEN HETEROZYGOUS PLANTS OF F1 GENERATION ARE CROSS BRED |
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Definition
| The offspring is F2 this means there is a ratio of 3 heterozygous dominant and 1 homozygous recessive offspring. |
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| In diploid organisms, characteristics are determined by alleles that occur only in pairs. Only one of each pair of alleles can be present in a single gamete |
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| XX so all gametes are the same because they contain a single X chromosome |
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| XY so half have a X chromosome and half have a Y chromosome |
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| Any gene that is carried on either the X or Y chromosome is said to be sex linked |
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Definition
| 23 pairs of chromosomes, 22 of these pairs have identical partners in appearance. One pair are the sex chromosomes, XX or XY |
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Term
RECESSIVE ALLELES ON THE X CHROMOSOMES |
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Definition
| X is longer than Y. Most of the length of X there is no equivilant homologous portion on Y that may have a dominant allele which would appear instead of recessive. Therefore recessive alleles on X appear more frequently in males than females. |
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Definition
X chromosome carries many genes
Haemophilia - blood clots slowly causing internal bleeding
Selective removal of the gene from population
Condition almost entirely males
Recessive allele - DNA nucleotides that don't code for the protein. Extracting this from donated blood can be given to haemophiliacs. No equivialant gene on Y because it doesn't carry the gene for producing clotting protein. Males only obtain Y from father, so can only inherit X from mother.
Fathers can pass down X to daughters |
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| Both alleles are equally dominant |
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| Where there are more than two alleles of which may be present at the loci of an individuals homologous chromosomes |
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| Both alleles of a gene are expressed in the phenotype. |
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FOR CO - DOMINANT ALLELES |
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Definition
Can't use upper and lower case letters, Must use different letters as superscript to represent alleles
e.g CW CR |
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WHEN DO MULTIPLE ALLELES OCCUR? |
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Definition
| When a gene has more than two alleles. e.g. human blood ABO blood groups. Although there are more than two alleles of this gene, only two can be present in an individual at any one time because there are only two homologous chromosomes so only two gene loci. |
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MULTIPLE ALLELES AND DOMINANCE HIERACHY |
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Definition
| The alleles are arranged in a hierachy with each allels being dominant to those below it and recessive to those above it. |
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Definition
All the alleles of all the individuals in a population at any one time.
This is used to refer to all the alleles of one particular gene in a population rather than all the genes. |
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| The numer of times an allele occurs within a gene pool |
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Definition
| Any individual human has two of every allele in every single cell however, as the alleles are the same in every cell, only one pair of alleles is counted per gene per individual. e.g 10,000 people 20,000 alleles of that gene in a gene pool |
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Definition
Total no. alleles taken to be 1.0
If everyone had homozygous FF then the frequency would be 1.0 for F and the frequency for f would be 0.0
If everyone was heterozygous Ff then the frequency for F would be 0.5 and f would also be 0.5
In practice, population is made up of a mixture of all 3 |
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Term
HARDY - WEINBERG PRINCIPLE |
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Definition
Can be used to calculate allelic frequencies under 5 conditions:
No mutations arise
Isolated population no flow of alleles
No selection - all alleles equally likely to be passed to next generation
Large population
Mating is random within the population |
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Term
HARDY - WEINBERG EQUATIONS |
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Definition
p + q = 1.0
p2 + 2pq + q2 = 1.0 |
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HOW DOES ALLELIC FREQUENCY CHANGE? |
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Definition
| Unless an allele leads to a phenotype with an advantage or disadvantage, it's frequency will remain constant from one generation to the next |
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Definition
| Only certain individuals reproduce successfully and so pass on thier alleles |
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REPRODUCTIVE SUCCESS AND ALLELE FREQUENCY
1 |
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Definition
| All organsims produce more offspring than can be supported by resources |
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REPRODUCTIVE SUCCESS AND ALLELE FREQUENCY
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| Populations remain constant even though too many have been produced |
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REPRODUCTIVE SUCCESS AND ALLELE FREQUENCY
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Definition
| Competition between members of a species as to who will survive |
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REPRODUCTIVE SUCCESS AND ALLELE FREQUENCY
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Gene pool contains wide variety of alleles
Some alleles are better suited to survive competition so can obtain more resources so more likely to survive and reproduce successfully. Only those that reproduce pass on genes so alleles that helped the parents are passed down to the next generation |
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REPRODUCTIVE SUCCESS AND ALLELE FREQUENCY
5 |
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Definition
New individuals have advantageous alleles so are more likely to reproduce passing down the advantageous alleles further.
Frequency of advantageous alleles increases and non decrease |
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WHAT DOES ADVANTAGEOUS DEPEND ON? |
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Definition
Environmental conditions
e.g camouflage in snow won't be camouflage in a hot climate |
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| Different environmental conditions favour different characteristics in the population |
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| Selection that favours in one direction of the mean of the population |
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| Favours average individuals, preserves characteristics |
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Definition
Characteristics are influenced by more than one gene. Influenced by environment
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If environment changes, so does the phenotypes
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| Environment remains stable, individuals with phenotypes closest to the mean are favoured |
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Definition
Evoulution of a new species from an existing species
Species share same gene pool
If populations become seperated, flow of alleles ceases.
Environmental factors for each isolated group differs to they adapt to thier environment
Selection favours for each environment
They evolve along seperate lines and eventually gene pools will become very different so can't breed, hence seperate species |
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Definition
| Physical barrier prevents two populations from breeding with one another e.g oceans, mountains, deserts, rivers |
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WHAT IF THE SPECIES ARE REUNITED? |
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Definition
| They won't be able to succesfully breed with each other |
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