selection Flashcards
mutation
change to the DNA base sequence
gene mutation
change to a single base in the DNA base sequence of a gene, they occur randomly and spontaneously
what might a mutation in DNA result in>
a change in the primary structure of polypeptides which may alter the secondary and tertiary structure, amking the protein non functional
subtitution (silent) mutation
substitution in the third base in a triplet
no effect on the polypeptide chain
substitution mutation (not silent)
at first base of triplet
changes the amino acid sequences so may alter tertiary structure and fucntion of protein
addition/deletion mutations
1 full dna nucleotide is gained or lost within a gene
results in an alteration of the base triplets from the mutation onwards - FRAME SHIFT
mutagenic agents increase..
the rate of spontaneous mutation
mutation agents egs;
high energy ionising radiation
DNA reactive chemicals
Biological agents - virus
genetic diversity
the number of different alleles of genes in a population
natural selection
variation exists within a population due to the formation of new alleles by mutation
better adapted individuals more likely to survive and reproduce
these organisms are more likely to pass on their alleles
those which are less well adapted fail to survive and reporduce
these organisms are less likely to pass on their allels
organisms are therefore subject to selection pressure due to the environment they live in
selection pressure determines the spread of an allele within the gene pool
biotic factors egs
number of predators
nmber of prey available
pathogens
food availability
presence of a mate
abiotic factors egs
wind intensity
temperature
soil pH
humidity
light intensity
stabilising selection
selection against both extremes
only mean phenotype will have reproductive success
alleles for mean phenotype are passed on to future generations in greater numbers
over time, frequency of mean alleles coding for the mean phenotype increases
alleles coding for both extreme phenotype decreases
HAPPENS IN STABLE ENVIRONMENT
directional selection
selection for only one extreme
individuals with advantageous alleles have increase reproductive success
alleles for one extreme are passed on to further generations in greater numbers
over time, frequenct of this extreme allele coding for the extreme phenotype increases
alleles coding for the other extremem phenotye decreases within the population
stabilising selection; birth weight in babies
selection agaisnt both extremes, low and high birthweight
the mean phenotype of medium borthweight is more likely to survive and reproduce successfully
alleles for medium birthweight are passed on to further generations in greater numbers
overtime frequency of the allele coding for medium birthweight increases
alleles for both extreme phenotypes decreases
directional selection; antibiotic resistance in bacteria
variation due to mutation to crease a new advantageous alleles that give antibiotic resistance
selection for advantgeous phenotype of antibiotics resistance and against non resistant bacteria if antiobiotics are taken
antibiotics resisttant bacteria re more likely to survive and reproduce
alleles for antibitoic resistance is passed on to future gens
overtime the freq of the allele coding for natibiotic resitance increases
increase in antibiotic resistant bacteria in the population
Inversion mutations
when a segment of bases is reversed end to en
Duplication mutations
A doubling of a part of a chromosome, of an entire chromosome, or even the whole genome
Translocation mutations
When groups of base pairs relocate from one area of the genome to another, usually between non-homologous chromosomes.
