Genetic diversity and adaptation Flashcards
Genetic diversity
Number of different alleles of genes in a population
What does genetic diversity enable to occur?
Factor enabling natural selection to 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
Directional selection
The alleles of an extreme type are selected for. For example, bacteria gaining antibiotic resistance:
A few bacteria have resistance.
Most of the population of bacteria suffer against antibiotics. But a few in the population have alleles that give them resistance.
A selection pressure is applied.
When antibiotics are given, a selection pressure is applied. The alleles giving antibiotic resistance are selected for.
The resistance alleles are selected for.
The resistant bacteria are more likely to survive and pass on their resistance alleles to the next generation
Bacteria evolve to become resistant. Over many generations, the bacteria evolve to become resistant.
Stabilising selection
The alleles of the mean / middle range are selected for.
This happens when the environment is stable, and the genetic diversity in a population decreases.
For example, human birth weight undergoes stabilising selection.
Human birth weight can vary. The weight of a baby can, of course, vary. But most babies have a weight in the middle range.
A normal birth weight is beneficial. Having too small or large birth weight can make it hard to survive. So a normal birth weight is selected for.
Natural selection keeps birth weights in the middle range. Natural selection stabilises the birth weights.
Atanomical adaptations
Polar bears are camouflaged against the snow.
Cacti have spines to prevent being eaten by animals.
Camel’s hump allows it to store energy.
Physiological adaptations
Tanning of skin when exposed to the sun over long periods
Formation of calluses on hands in response to repeated contact or pressure
Ability of certain organisms to absorb nutrients under low oxygen tensions
Behavioural adaptations
Diurnality and nocturnality, or being active during the day or night
Social behavior, or living by themselves or in groups
Behavior for protection, such as playing dead, freezing, or camouflaging
Migration, or moving to find food or mates
