2.2 a) Evolution - 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, changes in ___ ___ occur through random and non-random processes.
allele frequency
Name the random and non-random processes which change the frequency of alleles during evolution.
random: genetic drift
non-random: natural selection and sexual selection.
What does natural selection act on?
genetic variation in populations
Variation in traits arises as a result of ___.
mutations
Mutations are the original source of…
New DNA sequences
New sequences of DNA that are a result of mutations can be ___ ___.
novel alleles
What are novel alleles?
alleles that are new to a population and arise through mutations
Most mutations are ___ or ___, but some are…
harmful or neutral, beneficial to the fitness of an individual
When discussing natural selection, what is the first thing you should mention?
organisms produce more offspring than the environment can support
What is natural selection?
when individuals with variation which makes them better suited to their environment tend to survive longer, allowing them to pass on their beneficial alleles to the next generation
Natural selection results in…
the non-random decrease in deleterious alleles and increase in beneficial alleles
What is sexual selection?
the non-random processes involving the selection of alleles which increase an individual’s chances of mating and producing offspring (survival of the hottest)
What may sexual selection lead to?
sexual dimorphism
What is sexual dimorphism?
when males and females of the same species look different
Sexual selection can be down to… or…
male-male rivalry or female choice
What is male-male rivalry?
when males fight for access to females. large size or weaponry increases access to females
What is female choice?
when females assess the fitness of males for mating
What is genetic drift?
genetic drift is when chance events cause unpredictable fluctuations in allele frequencies
Genetic drift is more important in ___ ___ as alleles are more likely to be…
small populations, lost from the gene pool.
Which two effects involve genetic drift?
the bottleneck effect
the founder effect
What is a population bottleneck? (aka the bottleneck effect)
when the size of a population is reduced for at least one generation. alleles may be lost
Describe the founder effect.
The founder effect is when a few individuals are isolated from the larger population (eg by flying to an island). These few members breed and create a new population with a gene pool that does not represent the original population
How does genetic drift alter gene pools?
it changes the frequency of different alleles (by reducing/removing the some alleles, the frequency of all alleles changes)
As a result of genetic drift, some alleles may be ___ or ___ represented.
over or under
When selection pressures are strong, the…
rate of evolution can be rapid
What are selection pressures?
the environmental factors that influence which individuals in a population pass on their genes
Selection pressures can be ___ or ___.
biotic or abiotic
Name four biotic selection pressures.
competition, predation, disease, parasitism
Name five abiotic selection pressures.
temperature, light intensity, pH, humidity, salinity
What does the Hardy-Weinberg (HW) principle state?
in absence of evolutionary influences, the allele and genotype frequencies in a population will remain constant over generations
What are the five conditions for maintaining the HW equilibrium?
(aka what must we assume in order for the HW principle to work?)
- there is no gene flow (through immigration or emigration)
- no natural selection
- mating is random
- no mutations
- the population is large
What can the HW principle be used to determine?
whether or not a change in allele frequency is occurring over time
HW can be used to calculate ___, ___ and ___ frequency in a population.
allele, phenotype and genotype
What is the HW equation?
What other equation can you not live without?
p^2 + 2pq + q^2 = 1.
p + q = 1.
What do p and q represent in the HW equation?
the frequency of the dominant (p) and recessive (q) allele
What does p^2, 2pq and q^2 represent in the HW equation?
p^2 = frequency of the homozygous dominant genotype
2pq = frequency of the heterozygous genotype
q^2 = frequency of the homozygous recessive genotype
How do you answer HW questions?
- FInd the frequency of whatever allele/genotype they’re telling u about (x), by doing x / total population.
- If they are asking about genotype, then x/total population will equal p^2. If they are asking about allele frequency, then x/total population would equal p. Assume they will ask about the frequency of either of the homozygous genotypes (dominant or recessive). If they do, then find p by taking the square root of p^2
- Once you have found p, use the equation ‘p + q = 1’ to find the frequency of the other allele (q).
- sub in the values of p and q to the equation ‘p^2 + 2pq + q^2 = 1’. It should equal one
- assuming ‘p^2 + 2pq + q^2 = 1’ is true, then you can find the frequency of whichever of the 3 genotypes they’re asking about.
Natural selection is when individuals with ___ which makes them better suited to their ___ tend to survive ___, allowing them to pass on their ___ ___ to the next generation
variation, environment, longer, beneficial alleles
Evolution is the change over time in the ___ of ___ in a population differing in one or more ___ traits.
proportion, individuals, inherited
Selection pressures are ___ factors that influence which ___ in a population pass on their ___.
environmental, individuals, genes
The HW principle States that, in absence of ___ influences, the ___ and ___ frequencies in a population will remain constant over ___.
evolutionary, allele, genotype, generations
2022 P2 Q9.a):
Explain why genetic drift is likely to have occurred in the gene pool of Big Mountain Rockhorn sheep
Genetic bottleneck/founder effect
(1)
(causing) unpredictable/random changes in allele frequencies/gene pool.
OR
alleles lost/misrepresented/overrepresented/under-represented. (1)
*sometimes all they want is a definition, and you don’t have to link it to anything in the question
