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AQA GCSE Biology > Genetics > Flashcards

Genetics Flashcards

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1
Q

Where is DNA found in humans?

A

in chromosomes in the nucleus of cells

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2
Q

What do chromosomes contain?

A

1000s of genes

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3
Q

Why are chromosomes found in pairs?

A

one is maternal and the other is paternal

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4
Q

How many pairs of chromosomes do humans have?

A

23

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5
Q

What is DNA made of?

A

A polymer of nucleotides

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6
Q

What does each nucleotide contain?

A

a phosphate, a sugar and 1 of 4 bases

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7
Q

What are the four bases?

A

Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)

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8
Q

What codes for proteins?

A

The sequence of bases

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9
Q

What type of structure is the double stranded DNA molecule found in?

A

Double helix structure

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10
Q

What is the human genome?

A

The entire genetic material of a human

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11
Q

How many genes are present in the human genome?

A

30,000

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12
Q

Why is knowledge of the human genome important?

A
  • to search for genes linked to diseases
  • to understand and treat hereditary disorders
  • to trace human migration
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13
Q

What does each gene code for?

A

A protein

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14
Q

How many bases of DNA strand code for 1 of the 20 amino acids in a protein?

A

3

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15
Q

What does the sequence of the base determine?

A

The sequence of the amino acids

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16
Q

Is the double stranded structure stable or unstable?

A

Stable

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17
Q

Why does DNA have two strands?

A

One strand of DNA codes for genes, the other is complementary to it to give it strength

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18
Q

What are the pairs of bases in genes?

A

A binds with T

C binds with G

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19
Q

What are loacted either sides of genes?

A

Control regions which tell the body how often a gene needs to be expressed (used)

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20
Q

Describe the process of protein synthesis:

A
  • An enzyme will make a copy of the gene in a molecule called mRNA (messenger) which travels out the nucleus to a ribosome in the cytoplasm.
  • Here, each triplet (three bases), is paried with a tRNA(transfer) molecule with a specific amino acid attached.
  • The amino acids are joined together in a specific sequence to form a protein chain
  • This chain will fold in a specific way to make a protein with a specific shape e.g. enzyme
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21
Q

What is a DNA mutation?

A

Any change to the base sequence in DNA

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22
Q

What are the possible affects of a DNA mutation?

A
  • The amino acid sequence can be changed and the function of the protein can be thus affected e.g. changing the shape of an enzyme’s active site
  • The regulation of the gene can be affected, making it switch on more or less often than required
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23
Q

When do mutations occur?

A

Randomly during cell division

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24
Q

What factors increase the rate of mutations?

A

Radiation and carcinogens

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25
Q

What is the function of the cell cycle?

A

To control the replication of organelles and DNA so that cell division can occur

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26
Q

Describe the basic cell cycle:

A
  • Growth 1: replication of organelles
  • Synthesis: DNA replication
  • Growth 2: Replication of organelles and cell growth
  • Nuclear division: mitosis/meiosis
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27
Q

Describe the stages of mitosis:

A
  • DNA becomes visible in the nucleus
  • Nucleus disappears and chromosomes pair up
  • chromosomes line up down the middle of the cell
  • spindle fibres connect to the chromosomes
  • spindle fibres pull the chromosomes apart
  • nucleii form around the separated chromosomes
  • cell divides into two identical cells
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28
Q

What is the product of mitosis?

A

2 daughter cells that are identical to the parent cell are formed which are diploid

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29
Q

What does diploid mean?

A

They have 2 copies of each chromosome (ie. 23 pairs)

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30
Q

What is mitosis used for?

A

growth, repair and asexual reproduction

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31
Q

What is the product of meiosis?

A

4 non-identical haploid gametes

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32
Q

Describe the stages of meiosis:

A
  • The DNA in the cell replicates
  • The nucleus disappears and the chromosomes pair up together
  • The chromosomes line up in pairs down the middle of the cell. Spindle fibres attach to them and pull them apart
  • the first division creates two non-identical cells
  • the second division creates 4 haploid cells
  • 4 gametes are formed
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33
Q

Compare mitosis and meiosis:

A
  • 1 division vs 2 divisions
  • 2 daughter cells vs 4 daughter cells
  • identical cells vs non-identical cells
  • diploid vs haploid
  • growth,repair, aseual reproduction vs sexual reproduction
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34
Q

How is the diploid number of chromosomes maintained during fertilisation?

A

each gamete has 23 chromosomes so 23 (sperm) + 23 (egg) = 46 (zygote-fertilised egg)

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35
Q

What are the advantages of sexual reproduction?

A
  • introduces variation into offspring.
  • can lead to natural selection and evolution over time
  • artificial selection can be used to selectively breed desired traits
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36
Q

What are the advantages of asexual reproduction?

A
  • faster and more energy efficient
  • doesn’t require another parent/mate
  • lots of clones can be made if the environment is favourable
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37
Q

What organisms use both asexual and sexual reproduction?

A

malrial parasite, fungi and some plants

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38
Q

How do malarial parasties use both sexual and asexual reproduction?

A
  • asexual reproduction in humans

- sexual reproduction in mosquitos

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39
Q

How do fungi use both sexual and asexual reproduction?

A
  • asexual reproduction in spores

- sexual reproduction when required (ie. limited resources)

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40
Q

How do some plants use both sexual and asexual reproduction?

A
  • asexually with cuttings/runners

- sexually with seeds

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41
Q

What determines sex in an embryo and when?

A

The sex chromosomes (pair 23) at about 6 weeks after fertilisation

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42
Q

What chromsomes do females possess?

A

XX

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43
Q

What chromosomes do males possess?

A

XY

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44
Q

What type of chromsome does an egg have?

A

X

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45
Q

What type of chromsomes do sperm have?

A

50% X and 50% Y

46
Q

How many copies of each gene do we have? Why?

A

Two copies of each gene as we have two copies of each chromosome

47
Q

What is an allele?

A

A different version of a gene

48
Q

How many genes control fur colour in mice?

A

1

49
Q

What are the two mice fur alleles and which is dominant and which is recessive?

A

Black fur (dominant) and brown fur (recessive)

50
Q

What are the symbols for black fur and brown fur?

A

B and b

51
Q

What is the genotype of an organism?

A

The combination of dominant and/or recessive genes which an organism receives from their parents (e.g. BB for mice fur)

52
Q

What is the phenotype of a mouse?

A

The fur colour

53
Q

What is a mouse with a genotype BB called? WHat colour fur does it have?

A

A homozygous dominant - black

54
Q

What is a mouse with a genotype Bb called? What colour fur does it have?

A

A heterozygous - black

55
Q

What is a mouse with a genotype bb called? What colour fur does it have?

A

A homozygous recessive - brown

56
Q

What is a carrier?

A

An organism which carries a recessive gene in one of their two chromosomes so can pass it on to their offspring but display the dominant gene

57
Q

What does polygenic mean?

A

Means a characteristic is defined by many genes

58
Q

What type of diseases are cystic fibrosis and polydactyl?

A

Monogenic hereditary diseases

59
Q

What is cystic fibrosis?

A
  • living condition where a patient produces very thick sticky mucus which builds up in lungs, digestive system, reproductive system
  • it is recessive so 2 carries have a 1/4 chance of their child having cystic fibrosis
60
Q

What is polydactyly?

A
  • where someone grows extra fingers or toes

- it is dominant so a patient cannot be a carrier of it as the heterzygous individual will be a sufferer

61
Q

What are the disadvantages of sexual reproduction?

A
  • takes time and energy to find a mate or spread gametes so is less efficient
  • often slower than asexual reproduction
62
Q

WHat are the disadvantages of asexual reproduction?

A
  • if the environment changes, all offspring are at risk since they are genetically identical and may not survive
63
Q

Compare asexual and sexual reproduction:

A
  • Asexual requires one parent whereas sexual requires 2
  • fertilisation is used in sexual reproduction and mitosis in asexual reproduction
  • offspring from sexual reproduction are genetically different to one another and their parents whereas asexually reproduced offspring are genetically identical to their parent
64
Q

What does sexual reproduction in plants involve?

A

The joining of pollen and an ovule in fertilisation

65
Q

How do plants reproduce asexually?

A

runners form at the ends of exisiting stems by mitosis

66
Q

How will the genome project help identify which rare diseases are inherited?

A
  • the genome of a person with a rare disease can be compared to the genome of a relative
  • if the relative has the disease, DNA sequences that are similar can be looked for
  • if the relative does not have the diesease, scientists can look for DNA sequences that are different
  • these genes may be linked to the disease and mean it is inherited
67
Q

How will the genome project help to develop treatments for rare diseases?

A
  • if genes that are linked to diseases are identified, treatments can be developed
  • this could be genetic engineering to change a gene
68
Q

What is non-coding DNA?

A
  • DNA around a gene which switches the gene on and off but doesn’t actually code for a protein
69
Q

What is gene expression?

A

when a protein, coded for by a gene, is synthesised in a cell

70
Q

What can be used to show genetic crosses?

A

Punnett squares and family trees

71
Q

What is an allele?

A

A different version of a gene

72
Q

What does dominant mean?

A

That gene is always expressed if it is present

73
Q

What is a genotype?

A

The combination of alleles in an organism

74
Q

What is a gene?

A

A part of DNA made up of a specific sequence of nucleotides which code for a protein

75
Q

What is meiosis?

A

The process of cell division in sexual reproduction ehich produces 4 non-identical, haploid gametes

76
Q

What is a phenotype?

A

The expressed physical feature associated with a genotype

77
Q

When did Gregor Mendel publish his work?

A

1866

78
Q

Why was Mendel’s work originally rejected?

A

Most scientists believed in blended inheritance in which all characteristics are passed on

79
Q

When was the behaviour of chromosomes during cell division obeserved?

A

The late 19th century

80
Q

What was observed in the early 20th century?

A

That chromosomes and Mendel’s units behaved in similar ways. Led to idea that units (genes) were located on chromosomes

81
Q

What was discovered in the mid 20th century?

A

The structure of DNA and thus the mechanism of gene function

82
Q

What are stem cells?

A

Undifferentiated cells capable of dividing to produce more stem cells or specialising to make many different types of specialised cells.

83
Q

Where are stem cells located in animals?

A
  • in the embryo

- in bone marrow

84
Q

What is the difference between stem cells in bone marrow and embryos?

A

The stem cells in bone marrow can differentiate into a limited number of specialised cells like blood cells whereas those in embryos can differentiate into most human cells

85
Q

Where are stem cells located in plants?

A

In meristem tissue which is found behind the root and shoot tips and between xylem and phloem cells

86
Q

What is special about stem cells in plants?

A

They can differentiate into any plant cell throughout the life of the plant

87
Q

What are the two methods of cloning plants?

A
  • tissue culture

- cuttings

88
Q

What does cloning with cuttings involve?

A
  • removing a small part of a plant and using it to grow a new cloned plant via asexual reproduction
89
Q

What does tissue culture cloning involve?

A

where colned whole plants are grown from just a few cells from the parent plant

90
Q

What is the use of tissue culture and cuttings?

A

Useful for culturing economically and comercially important plants such as crops with disease resistance and preserving rare or endangered plants

91
Q

What is the therapeutic cloning of animals?

A
  • cloning of an organism so it has the same genes as another, meaning it can be used for replacement organs without the risk of immune system rejection
92
Q

What are the disadvantages with therapeutic cloning and organ replacement?

A

there is a risk of viral infection and many people are ethically opposed to it

93
Q

What are the two methods of making clones in animals?

A
  • embryo splitting

- adult cell cloning

94
Q

Describe the embryo splitting cloning process:

A
  • when an embryo is at the 16 cell stage it is split into either 2 or 4 new embryos
  • each of these is transferred into a surrogate mother’s uterus and the resulting young are all clones of one another
95
Q

Describe the adult cell cloning process:

A
  • nucleus from an adult cell is taken
  • nucleus from an egg cell is taken
  • the adult’s nuclues is put into the egg cell
  • this cell is then given an electric shock and culture medium, allowing the embryo to form
  • this is transferred to a surrogate and a cloned baby will grow
96
Q

Why is the egg cell with the adult nucleus given an electric shock?

A

To stimulate mitosis

97
Q

What is genetic engineering?

A

It is where a gene is taken from an organism, transferred into the genome of another organism of a different species, to provide desireable characteristics

98
Q

Describe the genetic engineering process:

A
  • gene is removed from the original species, using enzymes called Restriction Endonucleases
  • this gene is inserted into a vector, typically a virus or a plasmid
  • this is then used to insert the gene into the host organism
99
Q

What happens if animal or plant cells are engineered early in development?

A

The characteristics of the whole organism can be changed

100
Q

How have plants already been genetically engineered?

A
  • to grow better with higher yield in unfavourable conditions (e.g. drought or pest infested)
  • to be more nutritious
101
Q

How have bacteria been engineered to help diabetics?

A

They have been engineered to make human insulin

102
Q

What is the advantage of using bacteria making human insulin?

A

It makes the insulin more readily available, cheaper and more widely accepted by society

103
Q

What is the grounding for fears about GM crops?

A

The fact that long term effects have not been studied

104
Q

Describe how bacteria are used to produce human insulin:

A
  • functioning insulin gene is extracted from a human chromosome
  • a plasmid is taken from a bacterium and cut open with enzymes
  • gene is joined with the plasmid with enzymes
  • the new plasmid is taken up by the bacterium
  • gene is switched on to make bacteria produce insulin
105
Q

What features can be given to GM crops?

A
  • Pest Résistance
  • increased fruit size
  • increased nutrition
  • disease resistance
  • herbicide resistance
  • pesticide resistance
106
Q

What is the advantage of using tissue culture rather than taking cuttings?

A

Can create thousands of clones from one small piece of tissue which can’t be done with cuttings

107
Q

What is the disadvantage of tissue culture compared to cuttings?

A

Needs to be carried out using specialist equipment in a laboratory whereas cuttings requires none

108
Q

What is the advantage of adult cell cloning for producing animals with certain traits compared to embryo cell cloning ?

A
  • embryo cells cloning clones mixed DNA from a mother and father so possess a mixture of traits
  • Adult cell cloning means all the animals get the one set of DNA from the one animal known to have the good traits
109
Q

What is the name of the process where genetic engineering is used to cure illness?

A

Gene therapy

110
Q

Describe how gene therapy can be used to cure type one diabetes

A
  • healthy gene producing insulin can be cut out of Humans DNA and transferred into a vector like a virus
  • this can infect the persons cells and the healthy insulin gene is thus inserted into their DNA

AQA GCSE Biology (9 decks)

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