2. Key Area 2- Evolution Flashcards
Define evolution
Evolution is the change over time (over successive generations) in the proportion of individuals in a population differing in one or more inherited traits
During evolution, what do changes in the allele frequency occur through?
The non-random processes of natural selection and sexual selection and the random process of genetic drift
What is the field of biology that studies allele frequencies in populations and how they change over time?
Population genetics
What is allele frequency and how is it calculated?
Allele frequency refers to how common an allele is in a population
It is calculated by:
number of times the allele appears in the population/ total number of copies in the gene
What is natural selection?
The non-random increase in the frequency of advantageous alleles and the non-random decrease in the frequency of deleterious alleles
How does natural selection come about/ what effect does in have on species in an environment?
Natural selection acts on the genetic variation in populations. The variation in traits arises as a result of mutation. Populations produce more offspring than an environment can support so individuals with variations that are better suited to the environment tend to survive longer and produce offspring, passing on these alleles to their offspring giving an advantage to the next generation
What is mutation?
It 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
What is sexual selection?
The non-random process involving the selection of alleles that increase the individuals chances of mating and producing offspring. Sexual selection can be due to male to male rivalry or female choice
What is male to male rivalry?
Large size or weaponry increases access to females through conflict. Success in male-male rivalry can increase a males access to females for mating. The victorious male has an increased chance of acquiring a mate. Individuals compete with each other with ritualised displays of strength and stamina to warn off competitors or defend its mate
What is female choice?
Involves females assessing the fitness of males
What might sexual selection lead to?
Sexual dimorphism
What is sexual dimorphism?
The systematic difference in form between individuals of different sex in the same species
What is genetic drift, when does it occur?
It occurs when chance events (rather than natural selection) cause unpredictable fluctuations in allele frequencies from one generation to the next
What is the effect of genetic drift on larger populations?
Larger populations are unlikely to change quickly as a result of genetic drift as the sample is larger, the surviving population would tend to have a more accurate representation of the allele frequencies of the original population
What is the effect of genetic drift on smaller populations?
In smaller populations, alleles are more likely to be lost from the gene pool
What is the bottleneck effect?
Is an extreme example of genetic drift which occurs when the size of the population is seriously reduced from events like natural disasters
which dramatically reduces a population which rarely represents the genetic make up of the original population. The smaller the surviving population, the more susceptible the effects of genetic drift for generations until its numbers return to normal potentially causing even more alleles to be lost.
What is the founder effect?
Is an extreme example of genetic drift which occurs through the isolation of a few members of a population from a larger population to establish a colony. This means that alleles in the founding population may be present at different frequencies than in the original population causing the gene pool of the new population to not be a representation of that in the original gene pool.
How is a gene pool altered by genetic drift?
Certain alleles may be underrepresented or overrepresented and allele frequencies change
