9. Genetic diversity

Question 1

what is a gene mutation?

Answer 1

a change in the DNA base sequence of chromosomes

Question 2

what difference often arises due to substitution mutation?

Answer 2

a single different amino acid.

Question 3

why do some substitution mutations not affect the protein function at all?

Answer 3

degenerate DNA.

several codons can code for the same amino acid.

Question 4

in a deletion mutation, why is it unlikely that they polypeptide coded for will function correctly?

Answer 4

frame shift occurs, all bases after the deletion shift one place to the left. This means that an entirely different set of triplets are created

Question 5

what is the process called in which mutations in the number of chromosomes occurs?

Answer 5

chromosome non-disjunction

Question 6

in sexual reproduction, what fuses to give rise to a new offspring?

Answer 6

gametes

Question 7

what is a diploid number of chromosomes?

Answer 7

number of chromosomes. a diploid is two copies of each (2n)

Question 8

how many chromosomes does the average human have?

Answer 8

46. 23 pairs

Question 9

define homologous chromosomes

Answer 9

pairs of matching chromosomes

Question 10

in the first stage of meiosis, meiosis I, what seperates?

Answer 10

the homologous pairs

Question 11

What separates during meiosis II?

Answer 11

The two chromosomes in the homologous pair split up

Question 12

Name the two processes which increase genetic variation in the offspring which are a result of meiosis?

Answer 12

crossing over, independent segregation of chromosomes

Question 13

outline the process which occurs in meiosis I which increases genetic variation

Answer 13

crossing over. The chromatids wrap around each other and swap bits of genetic information.
This means each chromatid has the same genes but a different combination of alleles

Question 14

How many haploid daughter cells are produced from one diploid parent cell?

Answer 14

4

Question 15

define genetic diversity

Answer 15

the number of different alleles in a species/population

Question 16

outline natural selection

Answer 16

individuals with an allele that increases survival chance are more likely to survive, reproduce and pass on their genes. This leads to an increase of allele frequency of beneficial genes, which over time leads to evolution

Question 17

What causes bacteria to be resistant to antibiotics?

Answer 17

mutation in their DNA allows some bacteria to survive the use of antibiotics.
This enables those bacteria to survive and reproduce, passing on the resistant alleles to their offspring.

Question 18

what type of selection is exemplified by antibiotic resistant bacteria?

Answer 18

directional selection

Question 19

why are human birth rates an example of stabilising selection

Answer 19

babies at the extreme ends often do not survive

Question 20

give an example of anatomical adaptation that can result from natural selection

Answer 20

physical features such as an animals shape

Question 21

give an example of physiological adaptations that can result from natural selection

Answer 21

can include the ability to make venom, but also more general functions such as temperature regulation

Question 22

give an example of behavioural adaptations that can result from natural selection

Answer 22

can be inherited or learnt and include tool use, language and swarming behaviour

Question 23

what is a substitution of bases mutation?

Answer 23

a nucleotide in the DNA molecule is replaced with a nucleotide that has a differing hydrogenous base

Question 24

what effect does a substitution of bases mutation have on the final polypeptide?

Answer 24

the polypeptide produced will differ in a single amino acid.
this can affect the shape and function of the final protein

Question 25

what is a deletion of bases mutation?

Answer 25

a nucleotide is lost from the normal DNA sequence

Question 26

what effect does a deletion of bases mutation have on the final polypeptide?

Answer 26

the loss of a singular nucleotide can cause considerable changes in the DNA sequence the amino acid sequence of the polypeptide is completely different, therefore the polypeptide is unlikely to function correctly

Question 27

Why does a deletion of bases mutation have such a drastic effect on the final polypeptide?

Answer 27

because the sequence of bases is read in units of 3 bases, one deleted nucleotide causes all triplets to be shifted left by one base, and therefore read differently. Resulting in the formation of an entirely different protein

Question 28

what is a chromosome mutation?

Answer 28

changes in the structure or number of whole chromosomes

Question 29

what are the 2 forms of chromosome mutation?

Answer 29

changes in whole sets of chromosomes | changes in the number of individual chromosomes

Question 30

explain the chromosome mutation : changes in the whole sets of chromosomes

Answer 30

occur when organisms have three or more sets of chromosomes rather than the usual 2

Question 31

What condition is caused by changes in the whole sets of chromosomes

Answer 31

polyploidy, occurs mostly in plants

Question 32

explain the chromosome mutation : changes in the number of individual chromosomes

Answer 32

sometimes individual homologous pairs of chromosomes fail to separate during meiosis. This is known as non-disjunction and usually results in a gamete having either one more or one fewer chromosome. resultant offspring will have more of fewer chromosomes than normal in all their body cells

Question 33

what condition is caused non-disjunction, changes in the number of individual chromosomes

Answer 33

downs syndrome | individuals have an additional chromosome 21

Question 34

why is genetic variation considered a strength?

Answer 34

it allows a species to adapt to their environment through evolution

Question 35

list the stages of meiosis

Answer 35

``` DNA is replicated pairing of homologous chromosomes crossing over occurs independent segregation occurs separation of chromatids production of haploid cells ```

Question 36

define non-dysjunction

Answer 36

chromosomes fail to separate during meiosis division

Question 37

How do you calculate the number of possible chromosome mutations?

Answer 37

2 to the power of n where n = the number of pairs of homologous chromosomes e.g an organism with 4 homologous pairs of chromosomes can produce 16 combinations

Question 38

list the stages of 'crossing over' during meosis

Answer 38

when the chromosomes line up with their homologous partner in meiosis 1, the chromatids become twisted around each other during the twisting, tensions are created and portions break off and then may recombine with the homologous partner (known as recombination) there are always equal amounts crossed over so chromosomes stay the same length crossing over means that the maternal and paternal alleles can be mixed

Question 39

why do organisms differ, what factors contribute to this?

Answer 39

genetic diversity within a species - gene mutation - chromosome mutation - random factors associated with meiosis and fertilisation

Question 40

describe the three sources of genetic variation

Answer 40

mutation gene flow sexual reproduction

Question 41

what effects do mutations have on a species?

Answer 41

mutations are not very common mutations are usually harmful to a population mutations are usually selected against through evolutionary processes unless they provide an advantage

Question 42

how does genetic diversity lead to natural selection?

Answer 42

serves as a way for populations to adapt to changing environments with more variation, it is more likely that some individuals in a population will posses variations of alleles that are better suited to the environment those individuals are more likely to survive long enough to produce fertile offspring possessing that allele

Question 43

why is genetic variation essential for natural selection?

Answer 43

essential for natural selection because natural selection can only increase or decrease frequency of alleles that already exist in the population whereas genetic variation offers the ability to introduce new ones to the population

Question 44

what are selection pressures?

Answer 44

external agents which affect an organisms ability to survive in a given environment

Question 45

different types of selection pressures.

Answer 45

negative - decreases the occurrence of a trait positive - increases the proportion of a trait selection pressures may not remain constant, leading to changes in what constitutes a beneficial adaptation.

Question 46

describe natural selection.

Answer 46

predation, disease and competition means that there is competition for survival - each of these provide a different selection pressure individuals with certain combinations of alleles have adaptations that makes them more likely to reproduce their advantageous alleles are passed onto the next generations over many generations, the frequency of the advantageous alleles increases and the frequency of the non-advantageous alleles decreases. so the frequency of the successful phenotypes also increases in subsequent generations

Question 47

types of genetic variations...

Answer 47

mutations meiosis (crossing over) random fertilisation (new combinations)

Question 48

describe discontinuous variation

Answer 48

there are distinct categories with no overlap are controlled by a small number of genes are largely unaffected by the environment

Question 49

describe environmental variation

Answer 49

genes set limits environment determines where, within the limits, an organism lies usually due to polygenes graphs plot an example of a continuous variation - no categories to plot individuals - are controlled by a large number of genes - are significantly affected by the environment - normal distribution curve

Question 50

what is an example of environmental variation

Answer 50

height and weight

Question 51

name the 3 types of selection

Answer 51

directional disruptive stabilising

Question 52

describe genetic drift

Answer 52

the change in the frequency of an allele in a population over time

Question 53

when does genetic drift occur most often?

Answer 53

in smaller populations

Question 54

how are genetic drift and population bottlenecks linked?

Answer 54

the 'founding' population is only made up of a small number of individuals with a small number of alleles the new population has non-representative allele frequencies compared to the parent population genetic drift causes allele frequency to become different to the parent population

Question 55

describe speciation

Answer 55

the evolution of a new species from an existing species - gene pool isolation (gene flow barrier) - evolutionary changes (changes in allele frequency) - reproductive isolation (organisms can no-longer breed to produce fertile offspring)

Question 56

describe allopatric speciation

Answer 56

organisms are geographically separated organisms in each population experience different selection pressures different alleles will be advantageous in each population mutations occur differently in each population

Question 57

describe sympatric speciation

Answer 57

organisms live in the same habitat at the same time random mutations occur that cause an organism to be reproductively isolated from the other individuals normally requires the organisms to be able to reproduce asexually

Question 58

what can reproductive isolation be a result of?

Answer 58

seasonal changes, e.g. a change in flowering/mating season mechanical changes, e.g. genitalia are no longer complementary behavioural changes, e.g. a change in courtship behaviour chromosomal changes, e.g. a chromosome divides in two, or an organism becomes polyploid