U2) KA2) EVOLUTION - by drift and selection

Question 1

what is Evolution

Answer 1

• 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

Question 2

variation of traits arises as a result of _____

- what is this ?

Answer 2

• 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

Question 3

what is a novel allele

Answer 3

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

Question 4

what are the three possible effects of mutations on evolutionary fitness of an individual

Answer 4

• 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

Question 5

most mutations are ______ or ______, but in rare cases they may be ________ to the fitness of an individual

Answer 5

• deleterious , neutral

- advantageous

Question 6

what can cause evolution

how ?

Answer 6

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)

Question 7

what is genetic drift

Answer 7

• genetic drift is the random increase or decrease in frequency of inherited traits over a number of generations

Question 8

when does genetic drift occur

Answer 8

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

Question 9

what are two common occurring examples of the effects of genetic drift

Answer 9

• population bottlenecks

- founder effect

Question 10

population bottleneck

Answer 10

• 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

Question 11

founder effect

Answer 11

• 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

Question 12

why does genetic drift have greater effect in small populations

Answer 12

• 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

Question 13

gene pool

Answer 13

the stock of different genes in an interbreeding population

Question 14

a gene pool is altered by genetic drift . explain

Answer 14

a gene pool is altered by genetic drift because certain alleles may be under represented or over represented

Question 15

genetic variation

Answer 15

Genetic variation is the difference in DNA among individuals or the differences between populations.

Question 16

variation in traits rises as a result of _____

Answer 16

mutation

Question 17

natural selection acts on _____ ______ in populations

Answer 17

genetic variation

Question 18

what is natural selection

Answer 18

• a non random process which selects individuals based on their survival chances and thus increases their chances of passing on their inherited genes

Question 19

what does selection result in

Answer 19

• 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)

Question 20

summary of process of natural selection

Answer 20

• 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

Question 21

what is sexual selection

differentiate this from natural selection

Answer 21

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

Question 22

sexual selection is thought to be more important in habitats where food is abundant and predation is low. why?

Answer 22

the selected alleles don’t necessarily help in the general survival of the individual in terms of obtaining food or avoiding predators.

Question 23

sexual selection may lead to sexual ______

Answer 23

sexual dimorphism

Question 24

what is sexual dimorphism

Answer 24

• 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

Question 25

sexual dimorphism - what do differences in gender include

Answer 25

• differences in terms of size and colour

- in most cases of sd , the male is larger / heavier armoured/ has more conspicuous markings /structures / behaviours

Question 26

what is reversed sexual dimorphism - give an example

Answer 26

• 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

Question 27

sexual selection can occur through…

Answer 27

male-male rivalry

female choice

Question 28

what is male-male rivalry

Answer 28

• 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

Question 29

what is female choice

Answer 29

• 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

Question 30

what is a selection pressure

- where selection pressures are strong , the rate of evolution can be _____

Answer 30

• 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