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27 Cards in this Set
- Front
- Back
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What is genotype?
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The genetic constitution of an organism - the combination of allelees it has
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What is phenotype?
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The observable featuers of an organism - how its genotype is expressed and how it interacts with environment
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What is a gene?
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A section of DNA (a sequence of nucleotide bases) that codes for a specific polypeptide
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What is meant by diploid?
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Two alleles (copies) of each gene
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What are the 3 different genotypes?
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homozygous dominant
heterozygous homozygous recessive |
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What is a dominant allele?
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One that is always expressed in phenotype
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What is a recessive allele?
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One only expressed when dominant allele not present (not expressed in a heterozygous individual)
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What is meant by the term co-dominant?
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More than one allele contributes to phenotype
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Why do most sex-linked diseases not concern y-chromosomes?
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Y is shorter and has fewer genes - no homologous genes
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For what reasons might a deadly disease not be selected against?
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Individuals survive to reproductive age
Disease provides selective advantage carriers unaffected |
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What is haemophilia?
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Sex-linked disease - recessive allele fails to make factor 8 (blood clotting protein) leads to internal bleeding
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How are blood groups determined?
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multiple alleles lead to diff antigens on red blood cells
allele IA -- antigen A allele IB -- antigen B allele IO - no antigen |
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What is a Medelian population?
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Population of one species that can interbreed with each other and share a gene pool
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What is the gene pool?
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All the alleles of all the genes of all the individuals in a population at one time
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What is an allelic frequency?
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The number of times an allele occurs within the gene pool
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What 5 conditions must be met for Hardy-Weinberg principle to aply?
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No mutations
No selection of particular alleles no immigration/emigration/gene flow (isolated pop) large enough populaiton random mating |
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What does the hardy weingberg principle predict?
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Frequency of alleles of a gene remain constant from one generation to the next
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What is selection?
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Organisms with alleles
that provide a selective advantage are more likely survive, reproduce and pass on alleles |
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What is directional selection?
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following environmental change
and selection pressure alleles of organisms with an extreme phenotype (at one side of the mean) have selective advantage survive and reproduce more |
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What is stabilising selection?
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If environmental conditions are stable
alleles of organisms with standard phenotype close to mean (and not extreme) have selective advantage survive and reproduce more phenotypes at extremes eliminated |
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What is disruptive selection?
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selection against standard phenotype (of mean individuals)
Extremes have advantage and differential reproductive success Allele frequency increases |
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How do stabilising and directional selection affect distribution curves?
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Stablising = narrower and higher mean
Directional-same shape but shifted to left or right |
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What is the key difference between stabilising and directional selection?
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Stabilising preserves characteristics
Directional changes |
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What is speciation?
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Evolution of new species from existing species
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What is a species?
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a group of geneticall similar organisms that can interbreed with each other to produce fertile offspring. the belong to the same gene pool
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Describe the process of speciation
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mutation = genetic diversity
geographical isolation means no flow of alleles different environmental conditions/selection pressure diff allelles selected for allele frequency of diff alleles increases differences accumulate until no longer interbreed occurs over a long time |
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What are the 2 mechanisms of isolation?
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Allopatric - physically separated
Sympatric - not physical |
