Unit 2 - Topic 2 - Evolution - Section A - 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 do changes in allele frequency occur
Changes in allele frequency occur through the non-random processes of natural selection and sexual selection, and the random process of genetic drift
What does natural selection act on
Genetic variation in populations
How does variation in traits arise
Variation in traits arises as a result of mutation. Mutation is the original source of new sequences of DNA. These new sequences can be novel alleles. Most mutations are harmful or neutral, but in rare cases they may be beneficial to the fitness of an individual.
Describe natural selection
Populations produce more offspring than the environment can support. Individuals with variations that are better suited to their environment tend to survive longer and produce more offspring, breeding to pass on those alleles that conferred an advantage to the next generation.
What does the selection in natural selection result in for alleles
Selection results in the non-random increase in the frequency of advantageous alleles and the non-random decrease in the frequency of deleterious alleles.
What is sexual selection
The non-random process involving the selection of alleles that increase the individual’s chances of mating and producing offspring
What can sexual selection lead to
Sexual dimorphism
What can sexual selection be due from
Male-male rivalry and female choice
Describe male-male rivalry and female choice
Male-male rivalry: large size or weaponry increases access to females through conflict. Female choice involves females assessing the fitness of males
When does genetic drift occur
When chance events cause unpredictable fluctuations in allele frequencies from one generation to the next
When is genetic drift more important
In small populations, as alleles are more likely to be lost from the gene pool
When does population bottlenecks occur
When a population size is reduced for at least one generation
When does the founder effect occur
Through the isolation of a few members of a population from a larger population. The gene pool of the new population is not representative of that in the original gene pool.
Why is a gene pool altered by genetic drift
Because certain alleles may be under-represented or over-represented and allele frequencies change
