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GCSE - Biology > 7. Variation & Genetics > Flashcards

7. Variation & Genetics Flashcards

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1
Q

What do genes control?

A

The characteristics you develop.

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2
Q

How is each of your characteristics (e.g. hair colour) controlled?

A

There is a gene for each characteristic and the alleles of that gene you inherit determine that characteristic.

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3
Q

Are all characteristics controlled by a single gene?

A

No, some are controlled by multiple genes. (e.g. eye colour may be determined by several genes)

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4
Q

What are alleles?

A

Different versions of a gene. For example, the gene for hair colour has the allele for brown hair, the allele for blonde hair, the allele for black hair, etc.

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5
Q

How many versions (alleles) of each gene in your body do you have?

A

2 - one on each chromosome in a pair.

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6
Q

What does homozygous mean?

A

When the two alleles for a particular gene are the same.

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7
Q

What does heterozygous mean?

A

When the two alleles for a particular gene are the different.

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8
Q

What is a dominant allele?

A

The allele which determines the characteristic in a heterozygous or homozygous genotype.

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9
Q

What is a recessive allele?

A

The allele which only determines the characteristic in a homozygous genotype.

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10
Q

How are dominant and recessive alleles represented in genetic diagrams?

A

Dominant - Capital letters

Recessive - Lowercase letters

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11
Q

How can an organism have a recessive characteristic?

A

Both of the alleles in a pair must be the recessive allele.

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12
Q

What is genotype?

A

Which alleles you have.

e.g. Bb or bb

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13
Q

What is phenotype?

A

What characteristics you have.

e.g. blue hair phenotype or brown hair phenotype

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14
Q

What are genetic diagrams used to show?

A

The possible alleles of offspring.

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15
Q

What is genetic engineering?

A

The changing of an organism’s characteristics by replacing its genes.

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16
Q

How does genetic engineering work?

A

1) Useful gene is ‘cut’ from one organism’s chromosome using enzymes.
2) This gene is inserted into a vector which has also been cut beforehand - usually a virus (which inserts its DNA into the organism it infects) or bacterial plasmid (a small ring of DNA which can be passed between bacteria).
3) The vector is used to insert the gene into another organism (e.g. a bacterium) or into the chromosome of the different organism. The DNA is used to make a protein.

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17
Q

How can genetic engineering be used to produce insulin?

A

1) Enzyme is used to cut gene for insulin production from human DNA
2) Enzyme is used to cut plasmid DNA
3) The gene is inserted into the plasmid and the plasmid is replaced in the bacterium
4) The bacterium now produces insulin
5) The bacterium is grown until there is enough to produce insulin for diabetics.

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18
Q

How are viruses and bacterial plasmids used to insert a gene into another organism (genetic engineering)?

A

The viruses and bacteria insert the gene into another organism (e.g. a bacterium) or its chromosome (e.g. plants).

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19
Q

How can genes be transferred into animals and plants (genetic engineering)?

A

The genes have to be inserted at very early stages of development (shortly after fertilisation), allowing them to develop useful characteristics.

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20
Q

What are genetically modified crops?

A

Crop plants that have had their genes modified. This could be to make them resistant to viruses, insect attacks or herbicides.

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21
Q

Why is genetic engineering controversial?

A

Potential to solve many of our problems:
- Can be used to make proteins like insulin
- Hope of modifying human embryos to prevent genetic diseases
- Benefits of GM crop -> Solving world hunger
BUT
- Worries about long-term effects
- Transplanted genes could get out into the natural environment
- Ethical issues -> ‘Designer babies’
- Disadvantages of GM crops

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22
Q

What are the advantages of GM crops?

A
  • Can increase yield of crop, making more food
  • Could be engineered to provide nutrients which are missing from diets in less developed countries
  • Already being grown without problems in other parts of the world
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23
Q

What are the disadvantages of GM crops?

A
  • Could reduce biodiversity of surrounding species
  • Could be unsafe to eat (especially long-term), although unlikely
  • Transplanted genes could get out into the environment
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24
Q

Give an example of GM crops.

A

‘Golden rice’ which contains beta-carotene is being tested. Lack of beta-carotene causes blindness.

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25
Q

What are small differences between individual organisms in a species called?

A

Variation

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26
Q

What are the two types of variation?

A
  • Genetic variation

* Environmental variation

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27
Q

How is genetic variation caused?

A
  • Most animals inherit some genes from the mother and some from the father
  • This combining of genes causes genetic variation - no two of a species are identical
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28
Q

Give some examples of genetic variation.

A

• Eye colour
• Blood group
• Inherited disorders
These are genetic because they are entirely decided by genes and the environment has no bearing on them.

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29
Q

How is environmental variation caused?

A

• The environment that organisms live and grow in causes each organism to develop differently

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30
Q

Give some examples of environmental variation.

A

• Losing body parts
• Getting a suntan
• Plants having yellow leaves
These are environmental because they are only caused by the environment and genes have no effect on them.

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31
Q

Is variation strictly genetic or environmental?

A

No, characteristics can be due to genes and the environment.

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32
Q

Give some examples of characteristics which are both environmental and genetic.

A 
• Body weight
• Height
• Skin colour
• Academic or athletic ability
For example, the maximum height an organism could grow to is genetic, but it is the environment that determines whether it reaches that height.
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33
Q

What does DNA stand for?

A

Deoxyribonucleic acid

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34
Q

What is DNA?

A

A complex chemical that carries genetic information and is found in chromosomes in the nucleus of cells.

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35
Q

What is a gene?

A

A section of DNA that codes for a particular combination of amino acids, which are put together to make a protein.

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36
Q

How many amino acids are used in making proteins?

A

20

37
Q

How many different proteins can be made by genes?

A

Thousands

38
Q

How does DNA determine the type of cell a particular cell is?

A

The proteins which are produced determine the type of cell.

39
Q

What is the structure of DNA?

A
  • Two long strands coiled together in the shaped of a double helix.
  • The coils are held together by bases.
40
Q

How many types of base are there?

A

4

41
Q

What are the different types of bases?

A

A, T, C, G

42
Q

How does a gene determine the proteins produced by a cell?

A
  • Order of bases in a gene decides the order of amino acids in a protein
  • Each amino acid is coded for by 3 bases in the gene
  • These amino acids are joined together to make proteins
43
Q

Which pair of chromosomes determines your gender?

A

23

44
Q

What combinations can your 23rd pair of chromosomes be in?

A

XX or XY

45
Q

Which chromosomes do men have in their 23rd pair?

A

XY

46
Q

Which chromosomes do women have in their 23rd pair?

A

XX

47
Q

What is the probability of a couple having a male or female child?

A

50:50

48
Q

How is it possible for there to be a 50:50 chance of a child being male or female?

A
  • When making sperm, the X and Y chromosomes are drawn apart in the first division in meiosis.
  • After the second division, there are two sperm with the X chromosome and two with the Y chromosome.
  • When making eggs, the same happens except every egg has the X chromosomes (because the mother has XX chromosomes).
  • At fertilisation, this means there is a 50% chance of an XX combination and a 50% chance of an XY combination
49
Q

Remember to revise genetic diagrams

A

Pgs 69, 71, 72 of revision guide

50
Q

Who was Gregor Mendel?

A
  • An Austrian monk who trained in maths and natural history.
  • He carried out experiments on plants in his garden.
  • His research was published in 1866 and eventually became the foundation of modern genetics.
51
Q

What did Gregor Mendel’s experiments consist of and what were the results?

A

1) A tall pea plant and a dwarf pea plant are crossed
• The offspring were all tall pea plants
2) Two of the offspring are crossed
• The offspring were three tall and one dwarf pea plants

52
Q

What did Mendel’s experiments show?

A
  • The height characteristics of pea plants was determined by “inherited factors” (i.e. genes) from each parent.
  • The ratio of tall and dwarf plants showed that the factor for tall plants “T” was dominant over the factor for dwarf plants “t”.
53
Q

What conclusions did Mendel reach?

A

1) Characteristics in plants are determined by “inherited factors”
2) Inherited factors are passed on from both parents, one from each parent
3) Inherited factors can be dominant or recessive - if the offspring has both, the dominant characteristic is expressed

54
Q

Why did Mendel come to conclusions about “Inherited factors” and not genes?

A

In his time, no one knew about DNA. We now know that these “inherited factors” are genes.

55
Q

What is cystic fibrosis?

A
  • A genetic disorder of the cell membranes

* It results in a lot of mucus in the air passages and pancreas

56
Q

Is the allele that causes cystic fibrosis dominant or recessive?

A

Recessive

57
Q

How can cystic fibrosis be inherited?

A

Both parents must be carriers or sufferers and both must pass on the recessive allele to the child.

58
Q

What is polydactyly?

A
  • A genetic disorder

* Baby is born with extra fingers or toes

59
Q

Is the allele that causes polydactyly dominant or recessive?

A

Dominant

60
Q

How can polydactyly be inherited?

A

Either one or both of the parents must be a carrier of the dominant allele (and therefore a sufferer).

61
Q

What is sickle-cell anaemia?

A
  • A genetic disorder

* Characterised by unusually shaped RBCs, which get stuck in capillaries and deprive body of oxygen

62
Q

How does sickle-cell anaemia affect the body?

A

The unusual cells get stuck in capillaries, which deprives the body of oxygen. This results in symptoms such as tiredness, painful joints and muscles, fever and anaemia.

63
Q

What are the symptoms of sickle-cell anaemia?

A
  • Tiredness
  • Painful joints and muscles
  • Fever
  • Anaemia
64
Q

Is the allele that causes sickle-cell anaemia dominant or recessive?

A

Recessive

65
Q

How can sickle-cell anaemia be inherited?

A

Both parents must be carriers or sufferers and both must pass on the recessive allele to the child.

66
Q

What are the advantages of being a carrier of the sickle-cell anaemia allele and what has this resulted in?

A
  • Carrying the sickle-cell anaemia allele (Aa) makes you less likely to get malaria than if you’re homozygous for the dominant allele (AA).
  • This has resulted in an increase in carriers in areas where malaria is common.
67
Q

What causes Down’s Syndrome?

A

The inheritance of an extra chromosome. People with Down’s Syndrome have 47 chromosomes instead of 46.

68
Q

What does IVF stand for?

A

In vitro fertilisation

69
Q

What is in vitro fertilisation (IVF)?

A
  • When embryos are fertilised in a lab and then implanted into the mother’s womb.
  • More than one egg is fertilised, to increase the chance of success.
70
Q

What is embryo screening?

A

When a cell is removed from an embryo in IVF or from a mother’s womb and is then screened for genetic disorders.

71
Q

How does embryo screening work?

A

1) DNA is isolated from the embryo’s cells
2) A gene probe that will bind to the allele for a specific disorder is produced (the probe is a short section of DNA
3) The probe is labelled so it can be detected -> Usually, the label is a fluorescent chemical soho he can be seen under UV light
4) Probe is added to a mixture containing the DNA sample from the embryo. If the DNA contains the allele for the disorder, the probe binds to it.
5) Under a UV light, it is possible to tell whether the probe has binded

72
Q

What are some arguments FOR embryo screening?

A
  • It stops people suffering
  • Treating disorders costs the government a lot of money
  • There are laws to stop embryo screening going to far -> Parents cannot even select the sex of their baby (unless it’s far health reasons)
73
Q

What are some arguments AGAINST embryo screening?

A
  • It can lead to decisions about terminating pregnancy -> Ending a potential human life
  • Embryo screening isn’t always accurate -> Chance of terminating healthy embryo
  • Taking cells from womb increases chance of miscarriage
  • Implies that people with genetic problems are undesirable
  • Risk of everyone wanting to pick ‘desirable’ children
  • Screening is expensive
  • Some people think screening isn’t justified for genetic disorders that don’t affect a person’s health (e.g. polydactyly)
74
Q

What is sexual reproduction?

A

Where genetic information from two organisms (a father and a mother) is combined to produce offspring genetically different to either parent.

75
Q

How does sexual reproduction work?

A
  • Each parent produces a gamete with half the usual number of chromosomes.
  • At fertilisation, these fuse to give a full set of chromosomes, with a mixture of the mother’s and father’s genes.
76
Q

Why does sexual reproduction result in variation?

A

The offspring inherits half of its genes from the mother and half from the father, which results in the offspring being genetically different to both parents.

77
Q

What is asexual reproduction?

A

When a single parent produces a genetically identical offspring.

78
Q

How does asexual reproduction work?

A

By mitosis - an ordinary cell makes a new cell by dividing in two.

79
Q

What is a name for a copy of an organism produced by asexual reproduction?

A

A clone.

80
Q

What species reproduce asexually?

A
  • Bacteria
  • Some plants
  • Some animals
81
Q

What are the different methods of cloning?

A
  • Cloning plants by tissue culture
  • Embryo transplants
  • Adult cell cloning
82
Q

What is cloning by tissue culture?

A

Where a few plant cells are put in a growth medium with hormones and they grow into new plants - clones of the parent plant.

83
Q

What are the advantages of clogging plants by tissue culture?

A
  • Cheap
  • Quick
  • Very little space needed
  • Can be grown all year
84
Q

How can plants be cloned?

A

By tissue culture.

85
Q

How does embryo transplant cloning work?

A

1) Sperm cells are taken from the prize bull and egg cells are taken from the prize cow.
2) These are used to artificially fertilise one of the eggs.
3) The embryo formed is split several times before any of the cells become specialised.
4) These cloned embryos are implanted into other cows where they grow into baby calves.
5) Each of the offspring are identical to each other (although not to the parents)

86
Q

How does adult cell cloning work?

A

1) Unfertilised egg cell is taken and its nucleus is removed.
2) A complete nucleus is removed from an adult body cell and is placed into the egg cell.
3) The egg cell is stimulated by an electric shock to make it divide into an embryo.
4) After a while, the embryo is implanted into a surrogate mother so it can grow.

87
Q

What are some arguments AGAINST cloning?

A
  • Reduced gene pool -> Species more susceptible to disease
  • Cloned animals not as healthy as normal ones
  • Worries about human cloning
88
Q

What are some arguments FOR cloning?

A
  • Study of animal clones could lead to greater understanding of embryos, ageing and age-related disorders.
  • Preservation of endangered species

GCSE - Biology (11 decks)

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