The interaction between the expression of the genotype and the environment
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Definition of a mutation
Any change to the genotype as a result of a change to the DNA
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When may a mutation be inherited?
If the mutation occurs in the formation of gametes
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Definition of a modification
Any changes to the phenotypes which do not affect the genotype and therefore cannot be inherited
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Definition of a gene
A section of DNA (a sequence of nucleotide bases)
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How does a gene determine a characteristic?
By coding for particular polypeptides, which make up the necessary enzymes required for the biological pathway that leads to the production of the characteristic
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Definition of the term locus
The position of a gene on a chromosome
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Definition of an allele
One of the different forms of a gene
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Definition of homologous chromosomes
Pairs of chromosomes which occur in sexually reproducing organisms
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Definition of a dominant allele
The allele which is expressed in the phenotype of a heterozygous genotype
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Definition of a recessive allele
The allele which is only expressed in the phenotype in the homozygous recessive state
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Definition of co-dominant alleles
Alleles which both contribute to the phenotype (alleles are both dominant to some extent)
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Definition of the term 'gene pool'
All of the alleles of all the genes of all the individuals in a population at any one time
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Definition of the term 'allelic frequency'
The number of times an allele occurs within the gene pool
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Definition of a sex linked gene
Any gene that is carried on either the X or Y chromosome
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Why are men more likely to show a phenotype produced by a recessive allele carried on the X chromosome than women?
The male only has one allele, whereas, the female must be homozygous recessive in order for the allele to be displayed in the phenotype
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What conditions are required in order for the Hardy-Weinberg prinicple to apply?
1) No mutations arise 2) The population is isolated - no flow of alleles into or out of the population 3) There is no selection - all alleles are equally likely to be passed down 4) The population is large 5) Mating within the population is random
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Why aren't the observed ratios always the same as the expected ratios?
1) Fusion of gametes is random 2) The sample size may have been too small (the larger the sample size, the higher the validity)
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