2.Drift And Selection Flashcards
What is evolution?
Evolution is the change over time in the proportion of individuals in a population differing in one or more inherited traits.
During evolution, how does changes in the allele frequency occur?
- the non-random processes of natural selection and sexual selection
- the random processes of genetic drift
How does varaition arise?
As a result of mutation
What are most mutations?
Mutations are harmful or neutral and in some rare cases may be beneficial to the fitness of an organism.
What does natural selection act on
Genetic variation in populations
What is Natural selection?
A non-random increase in frequency of DNA sequences that increase survival.
What are the characteristics of natural selection?
- Population produces more offspring than environment can support
- There is variation amongst offspring
- There are selection pressures
- Individuals with a selective advantage survive to reproduce and pass of favourable alleles to their offspring.
- Those favoured alleles confer advantage to the next generation and become more frequent
What does selection result in?
The non-random increase in the frequency of advantageous alleles and the non-random decrease in the frequency in disadvantageous alleles.
What are selection pressures?
The environmental factors that influence which individuals in a population pass on their alleles.
What are examples of biotic selection pressures?
Competition (for food, a mate), predation, disease, parasitism
What are examples of abiotic selection pressures?
Change in temperature, light, humidity, pH and salinity
What does it mean if selection pressures are strong?
The rate of evolution can be rapid.
What is sexual selection?
Sexual selection is the non-random process involving the selection of alleles that increase the individuals’ chances of mating and producing offspring
What is sexual dimorphism?
Occurs in animals where there is a physical difference between males and females of the same species (other than in the sex organs)
What can sexual selection be due to?
Male-male rivalry and female choice
Why do males that have that increase access to females through conflict?
Large size or weaponry
What do females look for in assessing a suitable mate?
Fitness in terms of honest signals. Honest signals can indicate favourable alleles that increase the chances of survival of offspring (fitness) or a low parasite burden suggesting a healthy individual.
What is genetic drift?
Genetic drift occurs when chance events cause unpredictable fluctuations in alleles frquencies from one generaton to the next
When is genetic drift more important?
More important in a small population as alleles are more likely to be lost from the gene pool.
How is gene pool altered by genetic drift?
Certain alleles may be under-represented or overrepresented and allele frequencies change.
What is the founder effect?
An example of genetic drift that occurs when a small subpopulation randomly breaks away from a large population.
What is the bottleneck effect?
An example of genetic drift that occurs when a small subpopulation randomly survives when a large population reduces greatly.
What does Hardy-Weinberg principle state?
In the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over the generations.
What are the conditions for maintaining Hardy-Weinberg?
- No natural selection
- Random mating
- No mutation
- Large population size
- No gene flow (through migration, in or out)
What does p represent?
The frequency of the dominant allele
What does q represent?
The frequency of the recessive allele
What does p^2 represent?
Frequency of the homozygous dominant genotype
What does q^2 represent?
Frequency of homozygous recessive genotype
What does 2pq represent?
Frequency of heterozygous genotype
What does it mean if there is a change in the Hardy-Weinberg value?
That evolution is occurring
