U2) KA2) EVOLUTION - by 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
- the individuals in the population show genetic variation as they carry different versions of inherited traits
variation of traits arises as a result of _____
- what is this ?
- mutation
- mutation is a change in the DNA sequence
- different versions of inherited traits have different DNA base sequences as a result of genetic mutation
what is a novel allele
if a mutation results in a base sequence which codes for a different amino acid in a polypeptide , then the mutation has produced a novel allele
what are the three possible effects of mutations on evolutionary fitness of an individual
- a large number of mutations are neutral because there is no effect on the evolutionary fitness of an individual
- some mutations are harmful , because they reduce the individuals fitness
- very rarely some mutations are beneficial to the fitness of the individual
most mutations are ______ or ______, but in rare cases they may be ________ to the fitness of an individual
- deleterious , neutral
- advantageous
what can cause evolution
how ?
evolution can occur through
- the random process of genetic drift
- the non random process of natural selection and sexual selection
- they can cause evolution as all of these mechanisms cause changes to the frequency of inherited traits in a population (allele frequency)
what is genetic drift
- genetic drift is the random increase or decrease in frequency of inherited traits over a number of generations
when does genetic drift occur
genetic drift occurs when chance events cause unpredictable fluctuations in allele frequencies from one generation to the next
- certain alleles may be under represented or over represented following drift because the new population only carries a random sample of the original populations alleles
what are two common occurring examples of the effects of genetic drift
- population bottlenecks
- founder effect
population bottleneck
- occurs when a population size is randomly reduced for at least a generation , so lowering range of alleles upon which any selection pressure may then act on
founder effect
- a few members of the population are isolated from the larger population , the gene pool of the new population is not representative of the original one
why does genetic drift have greater effect in small populations
- alleles are more likely to be completely lost by chance from a small gene pool
- any change in allele frequency is likely to be more significant to the population as a whole
gene pool
the stock of different genes in an interbreeding population
a gene pool is altered by genetic drift . explain
a gene pool is altered by genetic drift because certain alleles may be under represented or over represented
genetic variation
Genetic variation is the difference in DNA among individuals or the differences between populations.
variation in traits rises as a result of _____
mutation
natural selection acts on _____ ______ in populations
genetic variation
what is natural selection
- a non random process which selects individuals based on their survival chances and thus increases their chances of passing on their inherited genes
what does selection result in
- results in the non random increase in the frequency of advantageous alleles and the non random decrease in the frequency of deleterious alleles(alleles which reduce fitness)
summary of process of natural selection
- population produces more offspring than the environment can support
- individuals with variations that are best suited to the environment are more likely to survive longer and produce more offspring
- the alleles for the favoured traits are inherited so they are more likely to become more frequent in subsequent generations
what is sexual selection
differentiate this from natural selection
sexual selection is the non random increase in the frequency of alleles that make mating and reproduction more likely
- sounds similar to natural selection, however , the selected alleles do not increase survival chances
sexual selection is thought to be more important in habitats where food is abundant and predation is low. why?
the selected alleles don’t necessarily help in the general survival of the individual in terms of obtaining food or avoiding predators.
sexual selection may lead to sexual ______
sexual dimorphism
what is sexual dimorphism
- sexual dimorphism means there are differences in characteristics between two sexes of the same species (other than their sex organs)
- both genders have distinct differences
- so that the fenale will select the male with the most desirable charatersitucs
sexual dimorphism - what do differences in gender include
- differences in terms of size and colour
- in most cases of sd , the male is larger / heavier armoured/ has more conspicuous markings /structures / behaviours
what is reversed sexual dimorphism - give an example
- some species of bird have reversed sexual dimorphism , where the female is larger / more bright coloured
- in many species of bird the female is larger- the male is better adapted for hunting small prey that are suitable for feeding his young nestlings during the breeding season
sexual selection can occur through…
male-male rivalry
female choice
what is male-male rivalry
- in male-male rivalry ,large size or weaponry -such as antlers , tusks, jaws, teeth and horns increase an individuals access to female through successful conflict with competing males
what is female choice
- female choice involves the female assessing the fitness of males through observing them : observing honest signals related to display, colour , plumes , calls and songs
- ‘honest signals’ are characteristics that allow potential mates to asses the genetic quality or fitness of the males
what is a selection pressure
- where selection pressures are strong , the rate of evolution can be _____
- selection pressures are the environmental factors that influence which individuals in a population pass on their alleles
- selection pressures can increase the heritability of beneficial traits and reduces the heritability of harmful traits
- selection pressures can be biotic(competition, predation, disease, parasitism) or abiotic (temperature, light. humidity, pH, salinity)
- rapid
