3.4 Topic 4 - 3.4.4 Genetic diversity and adaptation Flashcards
give the definition for genetic diversity
the total number of different alleles of genes in a population.
give the definition for a population
a population is a group of individuals of the same species that live in the same place and can interbreed
what does a species consist of?
one, or more populations.
genetic diversity is a factor enabling … to occur.
natural selection
list the 4 principles of natural selection in the evolution of populations
1} random mutation can result in new alleles of a gene.
2} many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success.
3} the advantageous allele is inherited by members of the next generation.
4} as a result, over many generations, the new allele increases in frequency in the population.
what does greater genetic diversity mean?
The greater the genetic diversity, the more likely that some individuals in a population will survive an environmental change.
This is because or a wider range of alleles and therefore a wider range of characteristics. This gives a greater probability that some individual will possess a characteristic that suits it to the new environmental conditions.
Differences between the reproductive success of individuals affects allele frequency in populations. How does this process work like?
- within any population or a species there will be a gene pool containing a wide variety of alleles.
- random mutation of alleles within this gene pool may result in a new allele of a gene which in most cases will be harmful.
- however in certain environments. the new allele or a gene might give its possessor an advantage over other individuals in the population.
- these individuals will be better adapted and therefore more likely to survive in their competition with others.
- these individuals are more likely to obtain the available resources and so grow more rapidly and live longer. As a result, they will
have a better chance of breeding successfully and producing more offspring. - Only those individuals that reproduce successfully will pass on their alleles to the next generation.
- therefore it is the new allele that gave the parents an advantage in the competition for survival that is most likely to be passed on to
the next generation. - as these new individuals also have the new, ‘advantageous’ allele, they in turn are more likely to survive, and so reproduce successfully.
- over many generations, the number of individuals with the new, ‘advantageous’ allele will increase at the expense of the individuals with the ‘less advantageous’ alleles.
- over time, the frequency of the new, ‘advantageous’ allele in the population increases while that of the ‘non advantageous’ ones decreases.
how does natural selection act on an individual?
by imposing a selection pressure.
stabilising selection simple definition + what environment does it take place in?
where natural selection favours an average phenotype, the selection pressures in stabilising selection select against the extreme phenotypes.
+ takes place in environments which do NOT change.
give an example of stabilising selection
human birth weights
if a baby has a below average weight = unlikely to survive.
if a baby has an above average weight = more likely to encounter difficulties during birth.
– stabilising selection selects for an phenotype within the average weight range.
directional selection simple definition + what environment does it take place in?
where natural selection favours one extreme phenotype, the selection pressures in directional selection select against all other phenotypes.
+ takes place after an environment has experienced change.
give an example of directional selection
antibiotic resistance
if bacteria are exposed to antibiotics = most of the population will not be resistant to its effects = not survive.
if a mutation evolved that confers resistance = selection will strongly favour bacteria with the resistant phenotype.
– the extreme, resistant phenotype is favoured.
what does directional selection result in?
it results in phenotypes at one extreme of the population being selected for and those at the other extreme being selected against.
what does stabalising selection result in?
it results in phenotypes around the mean of the population being selected for and those at both extremes being selected against.
what are the 3 types of adaptations which can occur from natural selection?
anatomical adaptations, physiological adaptations and behavioural adaptations
