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Biology > topic 6 - inheritance, variation and evolution > Flashcards

topic 6 - inheritance, variation and evolution Flashcards

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1
Q

what is sexual reproduction?

A
  • sexual reproduction involved the fusion of male and female gametes:
    -> sperm and egg cells in animals
    -> pollen and egg cells in flowering plants
  • in sexual reproduction, there is mixing of genetic information which leads to variety in the offspring. The formation of gametes involves meiosis.
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2
Q

what is asexual reproduction?

A
  • asexual reproduction involves only one parent and no fusion of gametes
  • there is no mixing of genetic information
  • this leads to genetically identical offspring (clones)
  • only mitosis is involved
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3
Q

what is fertilisation?

A

fertilisation is the fusion of the nucleus of a male gamete with the nucleus of a female gamete

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4
Q

where does meiosis take place in humans?

A
  • meiosis only takes place in reproductive organs
  • in humans that is the: testes in males and the ovaries in females
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5
Q

how are gametes formed?

A

cells in reproductive organs divide by meiosis to form gametes

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6
Q

what are the stages of meiosis?

A
  • all of the chromosomes are copied
  • the cell now divides into two
  • now, both of these cells divide one more time forming the gametes
  • in the gametes, the chromosomes are now single, not paired
  • each of these four gametes is genetically different from each other with different alleles
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7
Q

describe fertilisation and its resulting outcome

A
  • gametes join together to restore the normal number of chromosomes and the new cell then divides by mitosis
  • as the embryo develops, cells differentiate
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8
Q

what happens after fertilisation

A
  • the new cell divides by mitosis, producing a clump of identical cells - an embryo
  • as the embryo develops, the cells differentiate forming different cell types
  • in animals, these include nerve cells and muscle cells
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9
Q

what are advantages of sexual reproduction?

A
  • sexual reproduction produces variation in the offspring. this means that some of the offspring may survive if there is a change in environment -> sexual reproduction gives a species survival advantage by natural selection
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10
Q

what are the disadvantages of sexual reproduction?

A
  • two parents are required. this makes reproduction difficult in endangered populations or in species which exhibit solitary lifestyles
  • more time and energy is required so fewer offspring are produced
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11
Q

what are the advantages of asexual reproduction?

A
  • only one parent needed
  • more time and energy efficient as do not need to find a mate
  • faster than sexual reproduction
  • many identical offspring can be produced when conditions are favourable
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12
Q

what are the disadvantages of asexual reproduction?

A
  • risky because all the offspring are genetically identical, there is a risk they could all die if conditions become unfavourable
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13
Q

what are examples of organisms that reproduce by both methods of reproduction?

A
  • malarial parasites reproduce asexually in the human host, but sexually in the mosquito
  • many fungi reproduce asexually by spores but also reproduce sexually to give variation
  • many plants produce seeds sexually, but also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils
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14
Q

where do malarial parasites reproduce sexually?

A

mosquitoes

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15
Q

what conditions causes malarial parasites to reproduce sexually?

A

low temperatures

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16
Q

where do malarial parasites reproduce asexually?

A

liver and red blood cells in humans

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17
Q

where are chromosomes located?

A

chromosomes are found in the nucleus of cells

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18
Q

what do chromosomes contain?

A

the molecule DNA

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19
Q

what does DNA determine?

A

our inherited features

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20
Q

what is DNA?

A
  • DNA is a polymer made up of repeating units called nucleotides.
  • The polymer is made up of 2 strands that is twisted into a double helix
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21
Q

what is a gene?

A

a gene is a small section of DNA that codes for a particular sequence of amino acids, to make a specific protein

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22
Q

what is a genome?

A
  • the genome of an organism is the entire genetic material of that organism
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23
Q

what are the benefits of understanding the entire human genome?

A
  • understanding the human genome will help us to search for genes that are linked to a disease e.g genes that increase the risk of developing cancer or Alzheimer’s disease
  • understanding the human genome will help us to understand and treat inherited disorders e.g. cystic fibrosis
  • we can use the human genome to trace human migration patterns from the past - this helps people to discover their ancestry
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24
Q

where is the DNA located?

A

DNA is contained in chromosomes in the nucleus

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25
Q

what does a nucleotide consist of?

A

a phosphate group attached to a sugar molecule that is joined to a base

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26
Q

what never changes in a nucleotide in DNA?

A
  • in DNA, the phosphate group and sugar molecule never change
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27
Q

how many different nucleotides make up DNA?

A

4

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28
Q

what are the four bases?

A

A, C, G, T

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29
Q

which bases pair up together?

A

A-T
C-G

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30
Q

what are proteins?

A

polymers of amino acids

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31
Q

what is protein synthesis?

A

the formation of a protein from a gene

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32
Q

how many different amino acids are there in humans?

A

twenty

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33
Q

what does the specific order of amino acids determine?

A
  • the specific order of amino acids determines the shape of the protein
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34
Q

what does the shape of the protein determine?

A

the shape of the protein determines its function

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35
Q

how does a gene code for a protein?

A
  • a sequence of three bases in a gene forms a triplet
  • each triplet codes for an amino acid
  • the order of amino acids determines the structure and function of protein formed
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36
Q

what occurs during transcription?

A
  • in this stage, the base sequence of the gene is copied into a complementary template molecule
  • scientists call this template messenger RNA or mRNA for short
  • mRNA is a single stranded molecule
  • the mRNA now passes out of the nucleus and into the cytoplasm
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37
Q

what occurs during translation?

A
  • in this stage, the mRNA molecule attaches to a ribosome
  • amino acids are now brought to the ribosome on carrier molecules
  • these carrier molecules are called transfer RNA or tRNA for short
  • the ribosome now reads the triplets of bases on the mRNA and uses this to join together the correct amino acids in the correct order
  • once the protein chain is complete, it now folds into its unique shape
38
Q

what does the base sequence of a gene determine?

A
  • the base sequence of a gene determines the amino acid sequence of a protein
39
Q

what is a mutation?

A
  • a change in the base sequence of DNA
  • mutations occur continuously
40
Q

what are the effects of mutation?

A
  • most do not alter the protein, or only alter it slightly so that its appearance or function is not changed
  • if a mutation does not change the amino acid sequence, there is no effect on protein structure or function
41
Q

what happens if a mutation changes the shape of a structural protein?

A
  • it may lose its strength
42
Q

what are non-coding parts of DNA?

A
  • non-coding parts of DNA can switch genes on and off, so variations in these areas of DNA may affect how genes are expressed
43
Q

what are alleles?

A

different versions of the same gene

44
Q

what is a dominant allele?

A

a version of a gene where only one copy is needed for it to be expressed

45
Q

what is a recessive allele?

A

a version of a gene where two copies are needed for it to be expressed

46
Q

what is meant when an organism is homozygous?

A

when an organism has two copies of the same allele

47
Q

what is meant when an organism is heterozygous?

A

when an organism has two different versions of the same gene

48
Q

what is the genotype?

A

the genes present for a trait

49
Q

what is the phenotype?

A

the visible characteristic

50
Q

how are dominant alleles represented in a punnett squares?

A

they are represented using uppercase letters

51
Q

how are recessive alleles represented in a punnett square?

A

they use the lowercase version of the same letter as the dominant allele

52
Q

what is the problem with single gene crosses?

A

most characteristics are controlled by multiple alleles rather than just one

53
Q

what is an inherited disorder?

A

a disorder caused by the inheritance of certain alleles

54
Q

what are two examples of inherited disorders?

A
  • polydactyly = caused by a dominant allele
  • cystic fibrosis = caused by a recessive allele
55
Q

how are embryos screened for inherited disorders?

A
  • during IVF, one cell is removed and tested for disorder-causing alleles
  • if the cell doesn’t have any indicator alleles, then the originating embryo is implanted into the uterus
56
Q

what are the ethical issues concerning embryo screening?

A
  • it could lead to beliefs in society that being disabled or having a disorder is less human or associated with inferiority
  • the destruction of embryos with inherited disorders is seen by some as murder as these would go on to become human beings
57
Q

what are causes of variation in the characteristics of individuals?

A
  • the genes they have inherited
  • the conditions in which they have developed
  • a combination of genes and the environment
58
Q

what is genetic variation?

A
  • variations in the genotypes of organisms of the same species due to the presence of different alleles
  • creates differences in phenotypes
59
Q

what creates genetic variation in a species?

A
  • spontaneous mutations
  • sexual reproductions
60
Q

what are three types of gene mutation?

A
  • insertion
  • deletion
  • substitution
61
Q

how may a gene mutation affect an organism’s phenotype?

A
  • neutral mutation does not change the sequence of amino acids. Protein structure and function same. no effect on phenotype
  • mutation may cause a minor change in an organism’s phenotype
  • mutation may completely change the sequence of amino acids. this may result in a non functional protein -> severe changes to phenotype
62
Q

what is the impact of a new phenotype caused by a mutation being suited to an environmental change?

A

there will be a rapid change in the species

63
Q

what is the theory of evolution?

A
  • the theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago
64
Q

how many different species of animals and plants on the Earth?

A

9 million

65
Q

what is evolution?

A

evolution is the change in the inherited characteristics of a population over time through a process of natural selection

66
Q

outline the theory of natural selection (6)

A
  • genetic variation exists due to spontaneous mutations
  • selection pressures exist
  • random mutation gives an organism a selective advantage
  • organism is better adapted to the environment and survives
  • organism reproduces, passing on its beneficial alleles
  • frequency of advantageous alleles increase
67
Q

how do two populations become different species?

A
  • when their phenotypes become different to the extent that they can no longer interbreed to produce fertile offspring
68
Q

what is selective breeding?

A

the process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes

69
Q

outline the main steps involved in selective breeding

A
  • take a mixed population and select desired characteristics
  • we then breed this together
  • sexual reproduction produces variation in the offspring
  • select the male and female offspring of the desired characteristic and breed these together
  • continue doing this over many generations until all the offspring contain desired characteristic
70
Q

what is the problem with selective breeding?

A
  • if we breed together closely related animals or plants, then we can get inbreeding
71
Q

what can inbreeding cause?

A
  • inbreeding can cause some breeds to be prone to disease or inherited defects
72
Q

what are the main advantages of selective breeding?

A
  • crops produce a higher yield of grain
  • cows produce a greater supply of milk
  • plants produce larger fruit
  • domesticated animals
73
Q

what are examples of characteristics selected for in selective breeding?

A
  • disease resistance in crops
  • higher milk or meat production in animals
  • gentle nature in domestic dogs
  • large flowers
74
Q

what is genetic engineering?

A

a process which involves modifiying the genome of an organism by introducing a gene from another organism to give a desired characteristic

75
Q

what are examples of uses for genetically modified plants?

A
  • disease resistance
  • produce larger fruits
76
Q

what is a use for genetically modified bacteria cells?

A

to produce human insulin to treat diabetes

77
Q

what are the benefits of genetic engineering?

A
  • increased crop yields for growing population
  • useful in medicine
  • GM crops produce scarce resources
78
Q

what are the risks of genetic engineering?

A
  • long-term effects of consumption of GM crops unknown
  • negative environmental impacts
  • late-onset health problems in GM animals
  • GM seeds are expensive
79
Q

what is the name for crops that have had their genes modified?

A

genetically modified crops (GM)

80
Q

what is gene therapy?

A

gene therapy involves inserting copies of a normal allele into the chromosomes of an individual who carries the faulty cystic fibrosis allele

81
Q

what are the main steps in genetic engineering?

A
  • identify the gene that you want to transfer
  • use enzymes to isolate this gene
  • transfer the gene into a vector, usually a bacterial plasmid or a virus
    -this vector is used to insert the gene into the required cells
  • genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics
82
Q

what is tissue culture?

A

using small groups of cells from part of a plant to grow identical new plants
- this is important for preserving rare plant species or commerically in nurseries

83
Q

what are cuttings?

A
  • an older, but simple, method used by gardeners to produce many identical new plants from a parent plant
84
Q

what are embryo transplants?

A

splitting apart cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into host mothers

85
Q

what are the steps for adult cell cloning?

A
  • the nucleus is removed from an unfertilised egg cell
  • the nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell
  • an electric shock stimulates the egg cell to divide to form an embryo
  • these embryo cells contain the same genetic information as the adult skin cell
  • when the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development
86
Q

what was Charles darwin’s theory on evolution by natural selection?

A
  • individual organisms within a particular species show a wide range of variation for a characteristic
  • individuals with characteristics most suited to the environment are more likely to survive to breed successfully
  • the characteristics that have enabled these individuals to survive are then passed onto the next generation
87
Q

where did Darwin publish his ideas?

A

in ‘On the Origin of Species’ in 1859

88
Q

why was Darwin’s theory of evolution by natural selection only gradually accepted?

A
  • the theory challenged the idea that God made all the animals and plants that live on Earth
  • there was insufficient evidence at the time the theory was published to convince many scientists
  • the mechanism of inheritance and variation was not known until 50 years after the theory was published
89
Q

how can fossils give evidence for evolution?

A
  • older fossils simpler
90
Q

suggest how the insects came to be preserved in the amber

A
  • engulfed by resin
  • prevented decay

Biology (7 decks)

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