genetic diversity and adaptation Flashcards
why are there 7.3 billion people alive but they all look different
genetic diversity
what is the cause of genetic diversity
DNA determines the considerable variety of proteins that make up each organism
Therefore genetic similarities and differences between organisms may be defined in terms of variation in DNA
- therefore, DNA leads to genetic diversity
what do members of species have in common
a section of DNA that codes for one polypeptide is called a gene
members of the same species have the same genes
e.g. all humans have a gene for blood group and how all snapdragons have a gene for petal colour
how do organisms differ in phenotype -appearance
e.g. blood group in humans depends on which two alleles human possess - similar to what colour a snapdragon depends on
Therefore organisms of the same species differ in their combination of alleles, not their genes
what is gene diversity described as
it is described as the total number of alleles in a population
what is a population
a population is a group of individuals of the same species that live in the same place and can interbreed
how many populations do a species consist of
a species consists of one, or more populations
what determines how great the genetic diversity of a species is
the greater the number of different alleles that all species possess, the greater the genetic diversity if that species
what reduces genetic diversity
genetic diversity can be reduced when a species has fewer different alleles
why is having greater genetic diversity an advantage for a species/population
greater GD, the more likely that some individuals in a population will survive and environmental change
this is because of 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
what is genetic diversity a factor of
natural selection
why do certain alleles get passed on to the next generation
not all alleles of a population are equally likely to be passed to the next generation
This is because only certain individuals are reproductively successful and so pass on their alleles
what affects the frequency of different alleles in a population
difference between the reproductive success of individuals affects alleles frequency in a population
how do alleles get passed down to the next generation
- within any population of 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 allele of a gene might give its possessor and advantage in their competition with others
- 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 ad so grow more rapidly and live longer. As a result, they will have a better chance of breeding successfully and producing more offspring
- only these individuals that produce successfully will pass on their alleles to the next generation
- therefore is the new allele that gave the parents an advantage in the completion for survival that is most likely to be passed on to the next generation
- as the new individual also have the new “advantageous” allele, they turn are more likely to survive and reproduce successfully
what happens to the less advantageous alleles in the population
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
overtime, the frequency of the new alleles in the population will increase and the old alleles decrease
what does it mean when we say advantageous alleles
what is “advantageous” depend upon th environment conditions at any one time
e.g. alleles for black body colour may be “advantageous” as camouflage against a smoke-blackened wall but non- advantageous against a snowy landscape
what is selection
selection is the process by which organisms that are better adapted to their environment tend to survive and breed while those that are less adapted tend not to
what does selection depend on
different environmental conditions favour different characteristics in the population
- depending on which characteristics are favoured selection will produce a number of different results
what may selection favour
selection may favour:
- individuals that vary in one direction from the mean of the population
This is called DIRECTIONAL SELCTIONand changes the characteristic of the population
-average individuals.
This is called STABILISING SELECTION and preserved the characteristics of a population
what are characteristics influenced by
- more than one gene (polygenes)
these types of characteristics are influenced by the environment more than one determined by a gene
what are the effects of the environment on polygenes
the effect of the environment on polygenes produces individuals in a population that vary about the mean
when you plot this variation on a graph you get a normal distribution
what is directional selection
if environmental conditions change, the phenotypes that are best suited to the new conditions are most likely to survive
some individuals, which fall to either the left or right of the mean will possess a phenotype more suited to the new conditions
- these individuals will be more likely to survive and breed. They will, therefore contribute offspring and pass the alleles they possess to the next generation
over time the mean will then move in the dirc=ection of these individuals
what is an example of directional selection
antibiotic resistance in bacteria
e.g.
shortly after the discovery of antibiotics, t became apparent that the effectiveness of some antibiotics at killing bacteria reduced
It was fount that these populations of bacteria had developed resistance to antibiotics such as penicillin
It was found that these populations of bacteria had developed resistance to antibiotics such as penicillin
what was the resistance of the bacteria to antibiotics due too
the resistance was not due to the development of tolerance to the antibiotic, but rather a chance mutation within the bacteria