Genetic diversity and adaptation Flashcards
What is a mutation?
Any change to the quantity or the base sequence of the DNA of any organism.
Mutations occurring during the formation of gametes may be inherited, often producing sudden and distinct differences between individuals.
How can subsitution of bases be significant?
If it is important in forming bonds for tertiary structure, then the replacement amino acid may not form the same bonds and the protein may be a different shape, and not function properly.
If the protein is an enzyme, its active site may no longer fit the substrate and it will no longer catalyse the reaction.
What is substitution of bases?
A nucleotide in a DNA molecule is replaced by another nucleotide that has a different base.
For example, CTC codes for glutamine. If cytosine is replaced by guanine, the CTC becomes GTG, which codes for histidine.
The polypeptide produced will differ in a single amino acid, and the significance will depend upon the precise role of the amino acid.
How can substitution of bases not be significant?
If the new triplet of bases still codes for the same amino acid as before.
This is due to the degenerate nature of the genetic code, in which most amino acids have more than one codon.
For example, if the third base of GTC is replaced by thymine, it becomes GTT.
As both amino acids code for glutamine, there is no change in the polypeptide produced and so the mutation will have no effect.
What is deletion of bases?
When a nucleotide is lost from the normal DNA sequence.
The loss of a single nucleotide from the thousands in a typical gene can have considerable consequences.
Usually the amino acid sequence of the polypeptide is entirely different and so the polypeptide is unlikely to function correctly.
This is because the sequence of bases in DNA is read in units of three bases.
One deleted nucleotide causes all triplets in a sequence to be read differently because each has been shifted to the left by one base.
What is genetic diversity?
The total number of different alleles in a population.
A population is a group of individuals of the same species that live in the same place and can interbreed.
A species consists of one, or more, populations.
How is genetic diversity affected by species?
The greater the number of different alleles that all members of a species possess, the greater the genetic diversity.
Genetic diversity is reduced when a species has fewer different alleles.
How is genetic diversity affected by species and the environment?
The greater the genetic diversity, the more likely that some individuals in a population will survive an 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 natural selection in the evolution of populations?
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 is the first part of the process of reproductive success and allele frequency?
Within any population of a species there will be a gene pool containing a wide variety of alleles.
Random mutations 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 of 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.
What is the second part of the process of reproductive success and allele frequency?
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 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 one decreases.
What is selection?
The process by which organisms that are better adapted to their environment tend to survive and breed, while those that are less well adapted tend not to.
Every organism is subjected to selections, based on its suitability for surviving the conditions that exist at that time.
Different environmental conditions favour different characteristics in the population.
Depending on which characteristics are favoured, selection will produce different results.
What is directional selection?
Selection may favour individuals that vary in one direction from the mean of the population.
This changes the characteristics of the population.
What is stabilising selection?
Selection may favour average individuals.
This preserves the characteristics of the population.
What are polygenes?
Most characteristics are influenced by more than one gene.
These types of characteristics are more influenced by the environment than ones determined by a single gene.
The effect of the environment on polygenes produces individuals in a population that vary about the mean, and when plotted, you get a normal distribution curve.
