2.2a Drift and selection Flashcards
What is evolution?
the change over time in proportion of individuals in a population differing in one or more inherited traits
What happens during evolution?
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 variation in traits arise from?
mutations
What is a mutation?
the original source of new sequences of DNA
Explain mutations
- 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
How much do populations produce?
more than the environment can support
How does natural selection work?
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 selection result in?
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 may sexual selection lead to?
sexual dimorphism
What can sexual selection be due to?
- male-male rivalry
- female choice
What is male-male rivalry?
- large size or weaponry
increases access to females through conflict.
What is female choice?
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 and why?
- in small populations alleles are more likely to be lost from the gene pool
When do 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.
How is the gene pool altered by genetic drift?
certain alleles may be underrepresented or over-represented and allele frequencies change
What are selection pressures?
the environmental factors that influence which individuals in a population pass on their alleles.
When happens when the selection pressures are strong?
the rate of evolution can be rapid
What can selection pressures be and give examples?
- biotic
- competition
- predation
- disease
- parasitism
- abiotic
- changes in temperature
- light
- humidity
- pH
- salinity
What does the Hardy-Weinberg (HW) principle sate?
, 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 Hardy Weinberg principle?
- no natural selection,
- random mating,
- no mutation,
- large population size
- no gene flow (through migration, in or
out).
What can the Hardy Weinberg principle be used for?
determine weather a change in allele frequency is occurring in a population over time
the HW principle to calculate allele,
genotype and phenotype frequencies in populations.
What is the HW equation?
p^2+2pq+q^2=1
What do each of the letters in the HW equilibrium represent?
p = frequency of dominant allele
q = frequency of recessive allele
p^2 = frequency of homozygous dominant
genotype
2pq = frequency of heterozygous genotype
q^2 = frequency of homozygous recessive
genotype
