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27 Cards in this Set

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What is genotype?
The genetic constitution of an organism - the combination of allelees it has
What is phenotype?
The observable featuers of an organism - how its genotype is expressed and how it interacts with environment
What is a gene?
A section of DNA (a sequence of nucleotide bases) that codes for a specific polypeptide
What is meant by diploid?
Two alleles (copies) of each gene
What are the 3 different genotypes?
homozygous dominant

heterozygous


homozygous recessive

What is a dominant allele?
One that is always expressed in phenotype
What is a recessive allele?
One only expressed when dominant allele not present (not expressed in a heterozygous individual)
What is meant by the term co-dominant?
More than one allele contributes to phenotype
Why do most sex-linked diseases not concern y-chromosomes?
Y is shorter and has fewer genes - no homologous genes
For what reasons might a deadly disease not be selected against?
Individuals survive to reproductive age

Disease provides selective advantage


carriers unaffected

What is haemophilia?
Sex-linked disease - recessive allele fails to make factor 8 (blood clotting protein) leads to internal bleeding
How are blood groups determined?
multiple alleles lead to diff antigens on red blood cells

allele IA -- antigen A


allele IB -- antigen B


allele IO - no antigen

What is a Medelian population?
Population of one species that can interbreed with each other and share a gene pool
What is the gene pool?
All the alleles of all the genes of all the individuals in a population at one time
What is an allelic frequency?
The number of times an allele occurs within the gene pool
What 5 conditions must be met for Hardy-Weinberg principle to aply?
No mutations

No selection of particular alleles


no immigration/emigration/gene flow (isolated pop)


large enough populaiton


random mating

What does the hardy weingberg principle predict?
Frequency of alleles of a gene remain constant from one generation to the next
What is selection?
Organisms with alleles

that provide a selective advantage


are more likely survive, reproduce and pass on alleles

What is directional selection?
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

What is stabilising selection?
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

What is disruptive selection?
selection against standard phenotype (of mean individuals)

Extremes have advantage and differential reproductive success


Allele frequency increases

How do stabilising and directional selection affect distribution curves?
Stablising = narrower and higher mean

Directional-same shape but shifted to left or right

What is the key difference between stabilising and directional selection?
Stabilising preserves characteristics

Directional changes

What is speciation?
Evolution of new species from existing species
What is a species?
a group of geneticall similar organisms that can interbreed with each other to produce fertile offspring. the belong to the same gene pool
Describe the process of speciation
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

What are the 2 mechanisms of isolation?
Allopatric - physically separated

Sympatric - not physical