Drift And Selection Flashcards
What is the definition of evolution?
Evolution is the change over time in the proportion of individuals in a population differing in one or more inherited traits
During evolution what do changes in allele frequency occur through?
The non random process of natural selection and sexual selection, and the random process of genetic drift
What does natural selection act on?
Genetic variation in population
When does variation in traits arise?
As a result of mutation.
What is mutation the original source of?
New sequences of DNA
What can new sequences of DNA be?
Novel alleles
How can mutations affect the fitness of an individual?
Most mutations are harmful or neutral, but in rare cases they may be beneficial to the fitness of an individual
What is an example of a neutral mutation?
Widows peak
What is an example of a harmful mutation?
Sickle cell anaemia
What is an example of a beneficial mutation?
Antibiotic resistance in bacteria
What do populations that produce more offspring than the environment can support result in?
Selection pressures
What do individuals with variations that are better suited to their environment tend to do?
They tend to survive longer and produce more offspring, breeding to pass on those alleles that conferred an advantage to the next generation
What does selection result in?
The non-random selection increases in the frequency of advantageous alleles and the non random decrease in the frequency of deleterious alleles
What is sexual selection?
It is the non random process involving the selection of alleles that increase the individual’s chances of mating and producing offspring.
What may sexual selection lead to?
Sexual dimorphism
What is sexual dimorphism?
Where two sexes of the same species exibit different characteristics e.g. Lions, peacocks ect.
What can sexual selection be due to?
Male-male rivalry and female choice
What is male-male rivalry?
Large size or weaponry increases access to females through conflict e.g. male deer use antlers to compete for females
What is female choice?
involves females assessing the fitness of males. This may result in males attempting to “attract” elaborate displays
When does genetic drift occur?
It occurs when chance events cause unpredictable fluctuations in allele frequencies from one generation to the next
In what type of population is genetic drift more important and why?
It is more important in small populations, as alleles are more likely to be lost from the gene pool
What can genetic drift occur because of?
The bottleneck and founder effects
What is the bottle neck effect?
The population bottleneck effect occurs when a population size is reduced for at least one generation
What is the founder effect?
The founder effect occurs through the isolation of a few member of a population from a larger population. The gene pool of the new population is not representative of that in the original gene pool
What is a gene pool altered by?
A genetic drift because certain alleles may be under-represented or over-represented and allele frequencies change
What happens where selection pressures are strong?
The rate of evolution can be rapid. These selection pressures are the environmental factors that influence which individuals in a population pass on their alleles and they can be biotic or abiotic
What are examples of biotic factors?
-competition
-predation
-disease
-parasitism
What are examples of abiotic factors?
-changes in temperature
-changes in light
-changes in humidity
-changes in pH
-changes in salinity
What does the Hardy-Wineberg (HW) principle state?
It states that 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 the HW equilibrium?
-no natural selection
-random mating
-no mutation
-large population size
-no gene flow (through imigration, in or out)
What can the HW principle be used to determine?
Whether a change in allele frequency is occurring in a population over time. Changes suggest evolution occurring
What are the HW formulas?
p^2 + 2pq + q^2 = 1 (use when given Q about genotype)
p + q = 1 (use in Q of frequency of alleles)
-p=frequency of dominant alleles- f(A)
-q=frequency of recessive alleles- f(a)
-p^2=frequency of homozygous dominant genotype (individuals)- f(AA)
-2pq=frequency of heterozygous genotype- f(Aa)
-q^2=frequency of homozygous recessive genotype (individuals)- f(aa)
