3.4- Chapter 9- Genetic Diversity and Adaption

Question 1

What is genetic diversity within a species caused by and what does this result in.

Answer 1

• Gene mutation, chromasome mutation or random factors associated with meiosis and fertilisation.
• This is acted on by natural selection resulting in better adaptions.

Question 2

What are gene mutation and when can they occur?

Answer 2

• Gene mutations- involve a change in the base sequence of chromasomes to form a new allelle.
• Occur simultaneously during DNA replication.

Question 3

What are mutagenic agents and give examples.

Answer 3

• Factors that increase the rate of gene mutation.
• Increase probabiliy of mutation
• E.g. UV radiation, ionising radiation, chemicals and viruses.

Question 4

What can gene mutations be?

Answer 4

• Base deletion or substitution.
• Changes in base/ nucleotide sequence leading to hte formation of a new allelle.

Question 5

What are chromasome mutations and give the two types.

Answer 5

• Changes in the structure or number of chromasomes.
• Arise spontaneuously.
• Polyploidy.
• Non-disjunction.

Question 6

What is polyploidy and when does it occur.

Answer 6

• Changes in whole sets of chromasomes.
• Three or more sets of chromasomes rather than two.
• Lethal in humans so occurs mostly in plants- especially seedless plants/ hybrids of crops from selective breeding.
• Happens in meiosis when the chromasomes don’t seperate- e.g. if there are no spindle fibres.

Question 7

What does polyploidy cause?

Answer 7

• If odd number of chromasomes- too many chromasomes or too few- the organism becomes infertile.
• Homologous chromasome can’t pair so meiosis can’t occur as don’t seperate evenly.
• Normal cells have an even number of chromasomes and are therefore fertile.

Question 8

Why do mutations affect all the cells in the body?

Answer 8

Affects all cells in body as all derived of original zygote by mitosis.

Question 9

Name and describe the main type of chromasome mutation.

Answer 9

• Non-disjunction.
• Changes in number of individual chromasomes.
• Individual homologous pairs don’t seperate during meiosis.
• Rsults in one more or one fewer chromasome.
• If fertilised with normal gamete- offspring has one more or fewer chromasome than normal in all their cells.
• Happens during meiosis if chromasomes don’t divide properly- one cell may have two and one may have zero.
• Leads to inherited disorders e.g. Downs Syndrome- when fertilised cell has three copies of chromasome 21 in one cell and one in the other due to a failure to seperate during mitosis.

Question 10

What is a gene mutation?

Answer 10

Change in the base sequence of a gene resulting in the formation of a new allelle.

Question 11

Define substiution mutations.

Answer 11

One base is replaced with another/ one nucleotide is replaced with another nucleotide.

Question 12

Describe what substitution mutations cause?

Answer 12

• Polypeptide chain differs in a single amino acid.
• If amino acid is bond forming with a specific charge and determines tertiary structure and replaced with different or no bond forming amino acid or v.v.- may not form same tertiary structure and function properly.
• E.g. Enzyme- active site.

Question 13

When do substitution mutations affect the protien and when not?

Answer 13

• Degenerate genetic code- not all substitutions change the amino acid sequence- primary structure.
• Amino acids may be coded for by more than one codon- have the same codon
• Also may affect introns which have no affect.
• If replaces a bond-forming amino acid with an amino acid that forms the same bond (or no bond with no bond) then no effect

Question 14

What is a deletion mutation and what is its impact?

Answer 14

• One base/ nucleotide is lost from the DNA.
• Affects more than one amino acid- all triplets moved.
• Major impact- entire amino acid sequence can be different- causes a frameshift of bases to the left.
• The polypeptide is unlikely to function due to DNA being non-overlapping.

Question 15

When may a deletion mutation not have an impact?

Answer 15

If at the end of a gene.

Question 16

What do genes determine in protiens?

Answer 16

The DNA base order in a gene determines the order of amino acids of a polypeptide.

Question 17

What happens if a mutation occurs in a gene?

Answer 17

• The sequence of amino acids it codes for- primary structure- could be changed,
• Leads to a possible change in tertiary structure if involved in a bond and may limit function.

Question 18

When may a mutation not have an effect?

Answer 18

• May not change the tertiary structure if involved in the same bond.
• If in introns between genes.
• If degenerate substitution where a triplet codes the the same amino acid.
• If new allelle recessive- may have no effect on phenotype.

Question 19

What effect may some mutations have.

Answer 19

Some mutation may change the polypeptide to have positive changes- increased chance of reproductive success/ survival.

Question 20

What happens during sexual reproduction?

Answer 20

Two gametes fuse to create offspring.

Question 21

What does a normal gamete have?

Answer 21

• A half set of chromasomes- haploid.
• The number is the n number.
• Only contain one chromasome from each homologous pair.
• E.g. human haploids n-number is 23.

Question 22

When do gametes form?

Answer 22

• Gametes form half chromosome haploids during meiosis- especially animal cells.
• Some plants produce gametes by mitosis of aploids.

Question 23

What happens during fertilisation?

Answer 23

• Haploid sperm fuses with haploid egg restoring the diploid as a zygote.
• Half of the chromasomes are paternal and half are maternal.

Question 24

How does fertilisation increase genetic diversity?

Answer 24

• Fertilisation is random- any sperm can fertilise any egg- produces different zygotes with different combinations of homologous chromasomes.
• This increases genetic diversity.

Question 25

Describe normal body cells.

Answer 25

• Diploid- 2n of chromasomes.
• Contain homologous pairs of chromasomes- one maternal, one patrnal.

Question 26

What are homologous pairs?

Answer 26

Chromasome pairs with the same size and genes but potentially different allelles.

Question 27

How many chromasomes/ homologous pairs do humans have?

Answer 27

23 homologous pairs and 46 chromasomes.
Diploid (2n) number is 46.

Question 28

Why is meiosis important in terms of chromasomes?

Answer 28

• The number of chromasomes doesn’t double every generation which would happen if diploids fused.
• If diploids fused with haploids would create odd numberof chromasomes- creating infertility.

Question 29

What does mitosis create?

Answer 29

• Diploid from diploid cells.
• Haploid from haploid cells.

Question 30

Why do all body cells contain mutations if they occur from birth?

Answer 30

• All cells are derived from zygotes by mitosis.
• Mutations are in every cell as all cells are genetically identical.

Question 31

What does genetic variation enable?

Answer 31

Adaptions.

Question 32

What can cause genetic diversity?

Answer 32

• Meiosis- independent segregation of homologous chromasomes and crossing over.
• Random fertilisation.

Question 33

What is independent segration of homologous chromasomes and what does it result in?

Answer 33

• During meiosis 1 each homologous chromasome paris up- arrangement random.
• One of each pair passees to daughter cell- depends n how lined up.
• Random combinations of maternal and paternal chromasomees go into daughter cells- independent segregation
• Alleles in homologous pairs may differ so produces new genetic combinations.

Question 34

What is crossing over and what does it result in?

Answer 34

• Homologous pairs of chromasomes associate and twist around each oteher forming chiasma.
• This creates tension nad parts of the chromosome break off, enabling parts to rejoin with homologous partner.
• Usually the same parts are exchanged- equal lengths and alleles are exchanged.
• Results in new combinations of maternal and paternal alleles.
• Crossing over occurs many times and when broken parts recomine with another chromatid- this is recombination.

Question 35

Explain the importance of recombination.

Answer 35

• No recombination- only 2 types of cell from meiotic division.
• Recombination- 4 different types- no two cells are the same- increases genetic variation.

Question 36

Describe how random fertilisation produces genetic diversity.

Answer 36

• Random fertilisation- 2 different parents- two different genetic makeups- more variation- gametes are genetically different and fuse randomly.
• New maternal and paternal chromasome cominations.
• Haploids reform diploids.
• Different random fusion of haploids produces variety in offspring- new allelle combinations.

Question 37

Describe the process of meiosis- complicated one.

Answer 37

• Interphase- DNA unravels and replicates- 2 copies of each chromasome- chromatid.
• Prophase 1- DNA condenses to form double-armed chromasomes each made of sister chromatids joined by a centromere. Homologous chromasomes become closely associated and cross over. Nuclear envelope disappears and centrioles move to opposite poles and form spindle fibres.
• Metaphase 1- spindle fibres attatch to one side of each centromere. Two homologous chromosomes orientate and line up on the mataphase plate. Either maternal/ paternal orientate to a given pole.
• Anaphase 1- spindle fibres contract and pull chromatids towards poles- take both sister chromatids- complete haploid set of chromasomes- 1 member of each homologous pair.
• Telophase 1- nuclear membrane reforms and cell divides. Each ccell contains two sister chromatids joined at the centromere from each pair- not identical.
• Prophase 2- nuclear envelope breaks down and new spindle fibres form.
• Metaphase 2- spindle fibres bind to both sides of centromeres and line up on equator.
• Anaphase 2- spindle fibres contract- sister chromasomes move towards opposite poles.
• Telophase 2- nuclear envelope reforms and 4 genetically different haploid daughter cells produced.

Question 38

What is meiosis and how can this differ?

Answer 38

• Cell divison in reproductive organs.
• Forms haploid cells (gametes) from diploid.
• Mammals- gametes produced directly.
• Other organisms- produce haploids that divide by mitosis later to be gametes.

Question 39

Why is meiosis important?

Answer 39

Important so don’t get double chromasomes each time replication occurs.

Question 40

Describe the process of meiosis (simplified).

Answer 40

1. Before meiosis- DNA unravels and replicates- forms 2 copies of each chromasome called chromatids. DNA condenses to form double-armed chromasomes. Each have two sister chromatids joined by the centromere.
2. Meiosis 1- the first division- homologous chromasomes pair up and chromatids cross over. The chromasomes line up in a random arrangement and homologous pairs are seperated to opposite poles. One of each pair goes to the daughter cells. One maternal and one paternal chromasome goes to one of the two daughter cells.
3. Meiosis 2- second divison- sister chromatids divided by centromere.
4. 4 geneticallly different haploid daughter cells are produced.

Question 41

Draw a diagram of meiosis.

Answer 41

Answer on revision card.

Question 42

What is a gene?

Answer 42

A length of DNA that codes for a polypeptide.

Question 43

What is a locus?

Answer 43

The position of a gene on a chromasome/ DNA molecule.

Question 44

What is an allelle?

Answer 44

One of different forms of a particular gene.

Question 45

What are homologous chromasomes?

Answer 45

Pairs of chromasomes- one maternal and one paternal but both with the same gene loci.

Question 46

What must you remember when determining where meiosis occurs in a life cycle?

Answer 46

• Remember haploids are needed for sexual reproduction.
• Look for when goes from diploid to haploid.

Question 47

What must you remember when filling in numbers of chromasomes before/ after meiosis.

Answer 47

Remember number of chromasomes only halved in first division.

Question 48

What is key to remember about homologous pairs?

Answer 48

• Have the same genes.
• Determine the same characteristics.
• Allelles differ.

Question 49

What is the formula for the number of possible combinations of genes for independent segregation?

Answer 49

2ⁿ where n= number of homologous pairs.

Question 50

What is the formula for the number of possible combinations of genes after random fertilisation?

Answer 50

(2n)² where n= number of pairs of homologous chromasomes.

Question 51

What are predictions for the number of possible combinations of genes reliant on and why aren’t they definitive?

Answer 51

• Rely on intact chromasomes.
• Crossing over/ recombination- increases possible number of chromasomes.

Question 52

Compare meiosis to mitosis.

Hint: 8 points

Answer 52

• Cells with the same number of chromasomes- genetically identical to parent cell/ cell with half number of chromasomes to parent cell- **genetically different. **
• Daughter cells genetically identical to each other/ daughter cells genetically different to each other.
• Produces 2 daughter cells/ produces 4 daughter cells.
• One division/ two divisions.
• Diploid to diploid/ diploid to haploid.
• Mitosis has no pairing and seperation of homologus chromasomes, crossing over or independent segregation.

Question 53

What is genetic diversity?

Answer 53

• Genetic diversity is the number of different alleles of genes in a population (group of individuals of the same species that live in the same place and interbreed).
• The greater the number of allelles= greater genetic diversity.

Question 54

What is genetic diversity caused by?

Answer 54

• Gene and chromosome mutations- create new alleles, new combinations of alleles from meiosis and random fertilisation.
• Migration- new alleles added to the gene pool- gene flow.

Question 55

What is genetic diversity acted on by and what does this result in?

Answer 55

Acted on by natural selection, resulting in species becoming better adapted.

Question 56

Why is high genetic diversity important?

Answer 56

• Genetic diversity= more likely some organisms will survive an environmental change due to a wider variety of characteristics, which enables adaptation.
• Low diversity may result in the whole species being wiped out, for example, by a disease.

Question 57

Describe the effects of genetic bottlenecks.

Answer 57

• Caused by big reduction in in population e.g. if a population dies before reproducing due to hunting.
• This reduces the alleles in the gene pool and genetic diversity.
• The survivors reproduce and the larger population is created from a few individuals which result in high genetic diversity reduction.

Question 58

Describe the founder effect.

Answer 58

• Few organisms from a population start a new colony.
• Only a small number of initial of different alleles are in the initial gene pool.
• The allele frequency in the new horns colony may be very different to the original population and so rare alleles may be become more common, resulting in higher prevalence of genetic disease due to reduced genetic diversity and rarer unfavourable genes.
• Those without the disease are not selected in the same way.
• This can occur as a result of migration leading to geographic separation or due to enforced segregation.
• E.g. Amish People.

Question 59

Why are not all allelles equally likely to be passed on to the next generation?

Answer 59

Only certain individuals are likely to have reproductive success.

Question 60

What is the main factor affecting a little frequency?

Answer 60

Differences in reproductive success affect allele frequency.

Question 61

Describe natural selection.

Answer 61

1. Within any species, there is a gene pool with a wide variety of alleles.
2. Random mutations can sometimes result in new alleles of a gene, this is mostly harmful.
3. In certain environments, the new allele may be an advantageous allele- beneficial- gives organism a selective advantage.
4. These individuals are more likely to live longer, survive and reproduce, and therefore have increased reproductive success. Only individuals that reproduce successfully pass on their alleles, so individuals with an advantage are more likely to do this.
5. Therefore, the individual is more likely to pass on the advantageous allelle to the next generation.
6. If offspring have the new advantageous allele they are also more likely to survive and reproduce.
7. This means the advantageous allele is inherited by the next generation.
8. Over many generations the allele frequency of the advantageous alelle increases and the non advantageous alelle frequency decreases.

Question 62

What do advantageous features rely on and give an example?

Answer 62

Advantageous alleles depend on the environment e.g. with the peppered moth.

Question 63

What are most characteristics influenced by?

Answer 63

Process by which organisms are better adapted and allelle frequency is altered.

Question 64

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What are most characteristics influenced by?

Answer 64

• More than one gene (polygene).
• More influenced by environment than single genes.

Question 65

What do polygenes cause?

Answer 65

A variation around the mean- normal distribution curve.

Question 66

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What is variation measured using?

Answer 66

Differences in base sequences of DNA or amino acids in protiens.

Question 67

Describe directional selection.

Answer 67

If environmental conditions change- some individuals phenotypes mean htey are more likely to survive- right or left of mean- more likelyl to survive and reproduce- contribute more to next generation so mean shifts to direction of individuals- one extreme selected.

Question 68

Give an example of directional selection.

Answer 68

• Antibiotic resistance in bacteria.
• Resistance is due to mutations, not due tolerance. Mutations enable new proteins for example, enzymes to break down antibiotics.
• If some resistant bacteria with the mutation exist within an individual treated with the antibiotic- that bacteria has an advantage is more likely to survive and reproduce while the rest are killed.
• The bacteria would then reproduce by binary fission and antibiotic resistant members would be more likely to survive and multiply with than the non resistant bacteria.
• The resistant bacteria pass on their gene/ allelles as more antibiotic is used as there is less competition from non-resistant bacteria.
• As antibiotic resistance increases, the non resistant bacteria decrease, and the allele frequency of resistance increases.
• Normal distribution is shifted towards greater resistance, so the gene is passed on more.

Question 69

What is important to remember with antibiotic resistance and why mutations occur?

Answer 69

Mutations aren’t caused because of the antibiotic they are random. There are lots of bacteria. There will be lots of mutations, and some may occasionally be advanatious depending on environment. If the increased intake of antibiotics means that the resistant bacteria with the resistant mutation are more likely to survive.

Question 70

Draw the graph of directional selection.

Answer 70

Answer on revision card.

Question 71

When does stabilising selection occur and what is it?

Answer 71

• With a stable environment phenotypes closer to mean are more likely to survive or reproduce and pass on their allele’s.
• The extremes are less likely to survive, and this eliminates individuals phenotypes at the extremes.

Question 72

Give an example of stabilising selection.

Answer 72

• Human birth weights around the mean are selected while extremes are selected against.
• The body mass at birth of babies determines infant mortality. It is higher at extremes, usually in a log scale.
• There were another range of body masses at birth, where around these infant mortality is low.
• Our extremes infant mortality is high. There is a greater risk of death and weights around the mean are selected.
• The extremes are because very small babies are unlikely to survive as they have the high surface area to volume racial, so they find it hard to maintain their body temperature While large babies can’t through fit through the uterus, leaving to birth complications, therefore. medium sized babies are favourable and there is a shift towards these weights.

Question 73

Draw the graph of stabilising selection.

Answer 73

Answer on revision card.

Question 74

What does natural selection result in?

Answer 74

• Species becoming better adapted to their environment
• Better adapted individuals allele frequency increases, leading to evolution.

Question 75

Name the three types of adaptation and describe them.

Answer 75

• Behavioural. the ways organisms act increase their chance of survival. e.g. Possums playing dead or migration.
• Physiological processes increasing the chance of survive e.g. hibernation lowering metabolism and conserving energy, enzymes in bacterial resistance.
• Anatomical- structural features increase the chance of survival. e.g. Otters streamlined shape or arctic foxes thick fur.

Question 76

What must you do to when interpreting data on the graph of selection?

Answer 76

• Describe what the data shows.
• How it changes over time.
• Whether it shows directional or stabilising selections.
• Possible causes of what makes it more likely to survive reproducing pass on alleles over time to make them more common.
• Explain why the mean changes.

Question 77

What experiment is used to investigate selection.

Answer 77

• Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth.
• Shows how different allellles produce resistance to different antibiotics.

Question 78

Describe how you investigate the effect of antimicrobial substances on microbial growth.

Hint: 5 steps

Answer 78

1. Grow bacteria in broth.
2. Use a sterile pipette to transfer bacteria to the agar plate and spread the bacteria with spreader.
3. Use sterile forceps to place paper discs soaked with different antibiotics or disinfectant or antiseptics on the plate. Vary concentrations and types. Add a control disc soaked in sterile water.
4. Take the lid of the Petri dish and turn it upside down and incubate at 25°C for 48 hours. The bacteria should grow and patches should form- the inhibition zones.
5. The signs of the zone tells you the efficacy of the antibiotic, the larger the stone, the more bacteria inhibited. If there is no inhibition zone, the bacteria is resistant. The control must have no of inhibition to prove the results are due to the antibiotic and not the paper.

Question 79

Why are aseptic techniques important?

Answer 79

• Prevent contamination so you only test one microorganism.
• The ensure you don’t affect the growth of microorganisms (e.g. causing the spread of antibiotic resistant bacteria).
• Avoid contamination and culturing diseases causing microbes that make you ill.

Question 80

Describe aseptic techniques

Hint: 5

Answer 80

• Disinfect work surfaces to minimise contamination.
• Place utensils in a beaker of disinfectant- not on the work surface.
• Sterilise equipment and discard after use- glass should be steamed under high pressure and plastic discarded.
• Work near a bunsen so as hot air rises microbes are drawn away from the plate.
• Don’t keep the lid off the agar plate for too long to reduce chance of airborne microorganisms contaminating the culture.
• Flame the neck of the glass container with broth after opened and before closed- air moves out of the container, stopping microorganism entering.