Genetic Diversity and Adaptations Flashcards
(18 cards)
Genetic variation:
the small differences in DNA base sequences between individual organisms within a species population
Genetic diversity:
as the number of different alleles of genes in a population
what is genetic diversity a factor for?
enabling natural selection t occur
the principles of natural selection in the evolution of populations:
-random mutation can result in new alleles of a gene
-many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success
-the advantageous allele is inherited by members of the next generation
-as a result, over many generations, the new allele increases in frequency in the population
what do selection pressures do
they increase the chance of individuals with a specific phenotype surviving and reproducing over others
what is the advantage of a species having a large gene pool or high genetic diversity
the species will have a strong ability to adapt to change and vice versa for if they have small gene pool/ lower genetic diversity
the founder effect:
-the founder effect occurs when only a small number of individuals from a large parent population start a new population
-as the new population is made up of only a few individuals from the original population only some of the total alleles from the parent population will be present
-in other words, not all of the gene pool is present in the smaller population
-which alleles end up in the new sounding population is completely up to chance
-as a result, the changes in allele frequencies may occur in a different direction for the new small population vs the larger parent population
Genetic drift:
-when a population is significantly small, chance can affect which alleles get passed onto the next generation
-over time some alleles can be lost or favoured purely by chance
-when there is a gradual change in allele frequencies in a small population due to chance and not natural selection then genetic drift is occurring
Bottleneck effect:
-the bottleneck effect is similar to the founder effect
-it occurs when a previously large population suffers a dramatic fall in numbers
-a major environmental event can massively reduce the number of individuals in a population which in turn reduces the genetic diversity in the population as alleles are lost
-the surviving individuals end up breeding and reproducing with close relatives
what are selection pressures
environmental factors that affect the chance of survival of an organism
the two types of selection
-stabilising
-directional
stabilising selection:
-stabilising selection is natural selection that keeps allele frequencies relatively constant over generations
-this means things stay as they are unless there is a change in the environment
-a classic example of stabilising selection can be seen in human birth weights
-very-low and very-high birth weights are selected against leading to the maintenance of the intermediate birth weights
Directional selection:
-directional selection is natural selection that produces a gradual change in allele frequencies over several generations
-this usually happens when there is a change in environment/selection pressures or a new allele has appeared in the population that is advantageous
-for example, antibiotic-resistant bacteria strains are becoming more common due to the overuse of antibiotics
-the presences of antibiotics is a selection pressure, mutations are occurring in bacteria populations randomly, a mutation arises that confers antibiotic resistance - it’s a beneficial allele, bacteria with this mutation are more likely to survive and reproduce, most bacteria without the resistance mutation die, over generations this leads to an increase in the frequency of beneficial allele that produces antibiotic resistance
Adaptations can be:
anatomical, physiological or behavioural
natural selection will… and…
natural selection will select for favourable alleles that produce adaptations and will select against unfavourable alleles
Anatomical adaptations:
-structural/physical feature
-example: the white fur of a polar bear provides camouflage in the snow so it has less chance of being detected by prey
physiological adaptations:
-biological processes within the organism
-example: mosquitos produce chemicals that stop the animal’s blood clotting when they bite, so that they can feed more easily
behavioural adaptations:
-the way an organism behaves
-example: cold-blooded reptiles bask in the sun to absorb heat
