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A-level Biology Longridge Towers School > Chapter 9 Genetic Diversity > Flashcards

Chapter 9 Genetic Diversity Flashcards

1
Q

What is a mutation?

A

A random change in the DNA which results in a change to the sequence of bases.

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2
Q

How many bases in a codon?

A

Codons have 3 bases.

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3
Q

What strand is a codon on?

A

Codons are found on mRNA.

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4
Q

What base replaces Thymine in RNA?

A

Uracil

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5
Q

Where are anticodons found?

A

tRNA molecules

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6
Q

Explain the term degenerate in terms of the genetic code.

A

Although each codon is specific for only one amino acid (or one stop signal), the genetic code is described as degenerate, or redundant, because a single amino acid may be coded for by more than one codon.

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7
Q

What is a substitution mutation?

A

Replacement of a base of DNA.

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8
Q

What is a deletion mutation?

A

Removal of one of the bases in DNA.

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9
Q

What is an insertion mutation?

A

The insertion of one base in the DNA.

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10
Q

What is a frameshift mutation?

A

When an insertion or deletion results in the entire code being shifted by one base.

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11
Q

Which type of mutation is most likely to result in no amino acid change and why?

A

Substitution because the maximum change will be one incorrect amino acid in the entire protein. Due to the degenerate nature of DNA it is possible that the substitution will result in no changes to the amino acid sequence.

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12
Q

Describe the effects of a frameshift mutation on the amino acid sequence and the final protein.

A

Frameshift mutations result in errors in the codons for all amino acids following the mutation. This results in incorrect amino acid sequences and usually non-functional proteins.

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13
Q

What do mutagenic agents do to the probability of mutations occurring?

A

Mutagenic agents increase the probability of mutations occurring.

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14
Q

With no mutagenic agents present would you still get mutations? Why/why not?

A

Yes. Mutations randomly occur at a relatively constant rate.

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15
Q

Describe a positive effect of mutations.

A

The formation of new beneficial alleles. Mutations are the drivers of evolution.

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16
Q

What types of cells are produced by meiosis?

A

Gametes.

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17
Q

What are gametes?

A

Gametes are sex cells such as eggs, sperm, pollen and ovules.

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18
Q

What is an allele?

A

An allele is a different form of a gene. Alleles are created through mutation.

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19
Q

Name the stages in meiosis.

A

Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II

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20
Q

Briefly describe what happens at each stage in meiosis.

A

Interphase

Interphase is technically not a part of meiosis but it must take place before meiosis.
It involves the replication of DNA to produce genetically identical chromatids.
Prophase I

Chromosomes condense
Nuclear envelope disintegrates
Spindle fibres begin to form
Homologous chromosomes pair up
Crossing over occurs
Metaphase I

Chromosomes align on the cell equator
Spindle fibres attach to the kinetochore on the centromeres
Independent assortment occurs
The position of each homologous pair is independent of all the other chromosomes
The maternal and paternal chromosomes can be on either side of the equator
Anaphase I

Homologous chromosomes are pulled by the spindle fibres to the poles
This causes the genetic variation
Telophase I

Nuclear envelopes reform
Chromosomes uncoil
The cells undergo cytokinesis
These cells are now haploid cells
Prophase II

Beginning of second division:
Chromosomes re-condense
Nuclear envelope breaks down again
Spindle fibres reform
Metaphase II

Chromosomes are aligned on the equator by the spindle fibres
Independent assortment occurs again
More genetic variation is caused
Spindle fibres begin to attach to centromere
Anaphase II

Chromatids are split apart by the spindle fibres
Chromatids move to the poles of the cells
This is the same as anaphase in mitosis
Telophase II

Chromatids uncoil
Nuclear envelopes reform
The cell undergoes cytokinesis
4 haploid daughter cells are produced

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21
Q

Draw diagrams to show the stages in meiosis.

A
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22
Q

How many chromatids does a chromosome at Prophase I have?

A

2

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23
Q

What significant process happens during prophase I?

A

Crossing over

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24
Q

What significant process happens during metaphase I?

A

Independent assortment

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25
Q

Explain how independent assortment takes place. Use diagrams to illustrate it.

A

The way that a pair of chromosomes line up at the equator during metaphase I is independent of the way other chromosomes line up.

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26
Q

In a diploid organism with 16 chromosomes, how many combinations of chromosomes could there be after meiosis I? How can you work this out?

A

Use the formula combinations = 2n
With n = number of homologous pairs
If there are 16 chromosomes there are 8 pairs
Total combinations = 28
= 256

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27
Q

When does independent assortment of chromosomes occur during meiosis?

A

Metaphase I, Metaphase II

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28
Q

How many chromatids does a daughter chromosome have after they have been split in meiosis II?

A

Each daughter cell has 1 chromatid.

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29
Q

Describe a haploid nucleus. Which cells have a haploid nucleus?

A

A haploid cell only has one set of chromosomes in its nucleus. Gametes are haploid.

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30
Q

Describe a diploid nucleus. Which cells have a diploid nucleus?

A

A diploid cell has 2 sets of chromosomes in its nucleus. These are homologous pairs. Each pair codes for the same genes. All cells aside from gametes in humans are diploid.

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31
Q

What processes result in the 4 gametes produced being genetically different from each other?

A

Independent assortment

Crossing over

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32
Q

Give three differences between mitosis and meiosis.

A

Meiosis is reductive division - it produces 4 haploid cells. Mitosis results in 2 daughter cells that are diploid.

Meiosis involves 2 cell divisions, mitosis involves 1 cell division.

Meiosis produces cells that are genetically different from each other. Mitosis produces cells genetically identical to each other and also identical to the original cell.

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33
Q

What is nondisjunction and when does it happen?

A

Nondisjunction occurs during anaphase I or anaphase II when gametes are produced. It is caused by a failure of chromosomes to separate due to spindle fibre failure. It results in cells with an incorrect number of chromosomes.

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34
Q

Name 4 syndromes that are the result of nondisjunction.

A

Down Syndrome is also known as trisomy 21 and involves having an extra copy of chromosome 21.
Edwards’ Syndrome is also called trisomy 18 and involves having an extra copy of chromosome 18.
Turner Syndrome only affects females and involves missing one X chromosome.
Jacob’s Syndrome only affects males and involves having an extra copy of the Y chromosome.

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35
Q

Which stage of meiosis does crossing over occur?

A

Crossing over occurs during prophase I.

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36
Q

What is a chiasma?

A

A chiasma is a point of crossing over. It physically links the homologous chromosomes to each other.

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37
Q

What does the term ‘bivalent’ refer to?

A

Bivalent is a term used to describe a pair of homologous chromosomes linked by chiasmata.

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38
Q

Describe what happens during crossing over.

A

During crossing over chromatids from sister chromosomes form chiasmata. At each chiasma the DNA is broken, a section of DNA is swapped and the DNA joins together resulting in recombinant chromatids.

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39
Q

Why would happen if crossing over takes place between non-homologous chromosomes?

A

Non-homologous chromosomes do not code for the same genes. Crossing over between non-homologous chromosomes results in a mutation called a translocation.

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40
Q

What would happen if two chromatids from the same chromosome crossed over?

A

Genetically identical sections of DNA would be swapped leading to no change in the DNA and no recombinants produced.

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41
Q

What is the name for a crossover point?

A

Chiama (singular)
Chiamata (plural)

42
Q

How does crossing over increase genetic variation ?

A

Crossing over results in recombinants with a different combination of alleles than either original chromosome. All 4 gametes produced are genetically different from each other.

43
Q

How can you identify where meiosis has occurred in a lifecycle?

A

You can tell if meiosis has occurred because the chromosome number has halved (2n → n) or if a diploid individual is producing haploid cells.

44
Q

Name three gametes apart from sperm and eggs.

A

Ovules, pollen, spores

45
Q

What is genetic diversity?

A

Genetic diversity is the number of different alleles of genes in a population.

46
Q

What is genetic variation?

A

Genetic variation is the variation in the DNA sequence in each of our genomes. Essentially the genetic differences between individuals.

47
Q

How do mutations lead to genetic variation?

A

Mutations result in the formation of new alleles. This increases the variation between individuals of the same species.

48
Q

How does meiosis lead to genetic variation?

A

During meiosis independent assortment of chromosomes during anaphase I and II and crossing over during prophase I lead to recombinations of alleles and increase variation.

49
Q

How does sexual reproduction lead to genetic variation?

A

Sexual reproduction involves a random fertilisation event. This increases variation as no 2 zygotes produced from the same parents will be the same.

50
Q

Give 3 environmental factors that can result in variation within a population.

A

Climate

Food availability

Light intensity

51
Q

What are the steps involved in natural selection?

A

Random mutation can result in new alleles of a gene.

There is variation within a population.

Many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success.

The advantageous allele is inherited by members of the next generation.

As a result, over many generations, the new allele increases in frequency in the population.

52
Q

What is a selection pressure?

A

A selection pressure is an external agent which affects an organism’s ability to survive in a given environment. Selection pressures can be negative (decreases the occurrence of a trait) or positive (increases the proportion of a trait).

53
Q

Give 8 examples of selection pressures.

A

PANDA PAW
Predation

Availability of resources

Nutrient supply

Disease

Accumulation of waste

Phenomena (Natural disasters)

Abiotic conditions

Weather

54
Q

What is meant by selective advantage?

A

A selective advantage increases an organism’s ability to survive and therefore pass on its advantageous alleles to the next generation.

55
Q

Define evolution.

A

Evolution is the gradual change in the frequency of alleles in a population over time due to natural selection.

56
Q

What does ‘survival of the fittest’ mean?

A

“Fitness” means how well suited an organism is to its environment. Those best suited to their environment are more likely to survive long enough to reproduce and pass on their genes.

57
Q

What is another name for a Normal Distribution?

A

Gaussian distribution.

58
Q

What is the symbol for ‘population mean’?

A

µ

59
Q

What is standard deviation?

A

Standard deviation is represented by sigma σ. It shows how dispersed the data is relative to the mean.

60
Q

What type of graph do we often use to show the spread of the phenotype of a population?

A

We use histograms to show the spread of phenotypes in a population.

61
Q

What are the features of a histogram?

A

Histograms have bars that are the same width and without gaps between them.

62
Q

Give the 3 types of selection.

A

Stabilising, directional and disruptive.

63
Q

Draw a graph to show the effect of stabilising selection.

A
64
Q

Give an example of stabilising selection in action.

A

Human birth weights show stabilising selection. The mean is favoured. Extremes in birth weight increase the chance of death. Low birth weights increase the risk of stillbirth. High birth weights increase complications during labour and increase risk of death.

65
Q

Draw a graph to show the effect of directional selection.

A
66
Q

Give an example of directional selection in action.

A

Antibiotic resistance in bacteria is an example of directional selection. Use of antibiotics is selected for bacteria with resistance.

67
Q

Draw a graph to show the effect of disruptive selection.

A
68
Q

What are adaptations?

A

Adaptation, in biology, is the process by which a species becomes suited to its environment; it is the result of natural selection acting upon heritable variation over several generations.

69
Q

What are the three types of adaptation?

A

Anatomical
Behavioural
Physiological

70
Q

Why is adapting to live in extreme climates an advantage?

A

There is less competition in extreme environments.

71
Q

What is an anatomical adaptation?

A

Anatomical adaptations are physical features. These can be internal or external. They occur in plants and animals.

72
Q

What is a behavioural adaptation?

A

Behavioural adaptations are to do with the actions of an animal.. These can be innate or learned behaviours.

73
Q

What is a physiological adaptation?

A

Physiological adaptations are biochemical and happen inside the organism. Often these cannot be observed easily.

74
Q

Give examples of anatomical adaptations in plants.

A

Sunken stomata, waxy cuticle, seed shape, spines, swollen stems.

75
Q

Give examples of anatomical adaptations in animals.

A

Body covering (shells or fur), camouflage, teeth or beaks, mimicry, thick blubber, large body size.

76
Q

Give examples of behavioural adaptations in plants.

A

Phototropism, geotropism, ability to eat insects.

77
Q

Give examples of behavioural adaptations in animals.

A

Survival, hibernation, courtship.

78
Q

Give examples of physiological adaptations in plants.

A

Toxin production, CAM photosynthesis, seed dormancy.

79
Q

Give examples of physiological adaptations in animals.

A

Homeostasis, reflexes.

80
Q

How do bacteria reproduce?

A

Binary fission

81
Q

How is the nutrient agar medium sterilised when preparing to grow microorganisms?

A

Using an autoclave.

82
Q

What substances need to be present in a bacterial broth or nutrient agar?

A

The nutrient medium contains vitamins, nitrogen, carbohydrates and salts.

83
Q

Describe and explain the conditions in an autoclave.

A

The autoclave subjects the contents to high pressure, high temperature and steam.
This kills all microbes.

84
Q

Give the steps you would take to work aseptically.

A

Close windows and doors to reduce draughts and prevent sudden movements which might disturb the air.

Make transfers over a disinfected surface.

Start the operations only when all apparatus and materials are within immediate reach.

Complete all operations as quickly as possible, but without any hurry.

Vessels must be open for the minimum amount of time possible.

While vessels are open, all work must be done close to a Bunsen burner flame where air currents are drawn upwards.

On opening a test tube or bottle, the neck must be immediately warmed by flaming with the vessel held as near to horizontal as possible and so that any movement of air is outwards from the vessel.

During manipulations involving a Petri dish, limit exposure of the sterile inner surfaces to contamination from the air.

The parts of sterile pipettes which will be put into cultures or sterile vessels must not be touched or allowed to come into contact with other non-sterile surfaces, such as clothing, the surface of the working area, or the outside of bottles/test tubes.

All items which come into contact with microorganisms must be sterilised before and after each such exposure.

85
Q

Explain why you would work near a Bunsen burner when working aseptically.

A

Always work within 20 cm of a Bunsen flame. The convection current produced reduces the changes of environmental microbes contaminating your plate.

86
Q

How is the equipment sterilised during the practical?

A

Flaming in the Bunsen flame or disinfecting with ethanol.

87
Q

Describe the lawn plate spreading technique.

A

Add a few drops of the sample to the plate. Use a sterile L spreader to cover the plate evenly.

88
Q

What are two hazards of plating bacteria?

A

Contamination of microbes from the environment. These would then be cultured and could be harmful.

Release of sample microbes into the environment due to spills or poor technique.

89
Q

How is the agar plate stored after inoculation?

A

Plates are stored upside down in an incubator at 25°C.

90
Q

Why are plates stored upside down after inoculation?

A

Storing plates upside down reduces the formation of condensation on the lid. It also reduces the chances of bacteria landing on the agar surface.

91
Q

Explain the reasons for not sealing the lid to the agar plate using sticky tape after inoculation.

A

Sticky tape is used to keep lids closed. Closed lids are never opened in a school. We do not completely seal the plates because this creates an anaerobic environment that promotes the growth of dangerous pathogenic anaerobic bacteria such as E. coli.

92
Q

Explain the reasons for incubating at 25°C after inoculation.

A

A temperature of 25°C promotes growth as enzymes will work faster at warmer temperatures. We do not heat above 25°C because incubating at temperatures near to human body temperature may promote the growth of human pathogens.

93
Q

Describe how you would make a serial dilution of a bacterial culture that has a dilution factor of 10.

A
94
Q

What is the zone of inhibition?

A

The area around an antimicrobial disc where there is no growth of microbes.

95
Q

What can the zone of inhibition be used for?

A

To measure the effectiveness of microbial agents on reducing microbe growth.

96
Q

Give three examples of antibiotics.

A

Antibiotics
Amoxicillin, Ampicillin and Penicillin —inhibit steps in cell wall synthesis (prevents the building of new cell walls so cells cannot divide)

Norfloxacin – inhibits DNA replication so cells cannot divide

Erythromycin—inhibits RNA translation for protein synthesis so the cell cannot function

97
Q

Why do we use the disc diffusion method for determining the effectiveness of antibiotics?

A

It allows multiple antibiotics to be tested at once allowing the results to be more valid.

98
Q

What is a CFU?

A

A CFU is a colony forming unit. Basically it is a living bacterial cell that is capable of dividing and forming a colony on a plate.

99
Q

Why is a multidisc better to use than individual pre-soaked discs of antibiotics?

A

For the comparisons to be valid the concentration of antibiotic on each disc must be the same. Multi Discs are prepared industrially ensuring the concentrations are the same.

100
Q

How does the antibiotic get into the agar?

A

The antibiotic diffuses into the agar. This results in antibiotic concentrations being higher closer to the disc and decreasing as the distance from the disc increases.

101
Q

What is the MIC?

A

The minimum inhibitory concentration. This is the lowest concentration of antibiotic needed to inhibit the growth of the bacteria. It is used to determine dosage to give patients.

102
Q

Give 4 reasons why the dosage given to patients is always more than the MIC?

A

It is possible that not all of the antibiotics are absorbed.

Some of the antibiotics may get metabolised in the body or excreted.

A higher dosage ensures that all of the bacteria will be killed.

There may be some bacteria that possess antibiotic resistance

A-level Biology Longridge Towers School (37 decks)

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