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3 Flashcards

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1
Q

What is a gene?

A

A heritable factor that is one length of DNA. It influences characteristics.

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2
Q

What is a chromosome?

A

Many genes

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3
Q

What is the specific position that a gene occupies on a chromosome?

A

The locus

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4
Q

What are alleles?

A

Various forms of genes

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5
Q

How many alleles can occupy each locus?

A

1

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6
Q

How many copies of each chromosome do animals and plants have, and what does this mean?

A

Animals and plants have 2 copies of each chromosome, which means that they can have 2 different alleles for the same gene.

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7
Q

What are differences between alleles?

A

They differ by only one or a few bases

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8
Q

What is genetic mutations?

A

Where new alleles are formed through random changes, most significantly through base substitution.

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9
Q

What do mutations in cells that develop into gametes cause?

A

Genetic disease

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10
Q

What is the cause of sickle cell anaemia?

A
  • It is caused by a change to the base sequence of mRNA transcribed and therefore a change to the polypeptide sequence in haemoglobin. mRNA produces has GUG instead of GAG and produces valine, not glutamic acid.
  • it is a change to the gene Hb. Most humans have allele Hb4.
  • base mutation covered 6th colon of gene GAG to GTG, forming a new allele.
  • offspring inherits it if it occurs in the cell of ovary or testes that develop into gametes.
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11
Q

What is sickle cell anaemia?

A

A genetic disease that causes haemoglobin molecules to stick together in tissues with low oxygen concentration. Red blood cells change into a sickle shape and can become trapped in the capillaries, with a risk of stroke and blood flow reduction. In a high oxygen concentration, cells return to a normal shape, so they change with circulation. Th life of red blood cells is reduced to 4 days minimum.

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12
Q

What is a genome?

A

The whole of the genetic information of an organism, the entire base sequence of each of its DNA molecules.

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13
Q

What does the human genome consist of?

A

46 molecules, the same number as it’s chromosomes

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14
Q

What does a plant genome consist of?

A

DNA molecules of chromosomes in their nucleus, mitochondria and chloroplasts

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15
Q

What is the human genome project?

A
  • the entire base sequence of human genes

- began in 1989, published in 2003.

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16
Q

What did the human genome project show?

A
  • it helps us predict protein coding genes (23,000 in genome)
  • showed us that most of the genome is not transcribed, and that there is junk DNA, repetitive sequences
  • that humans majoritively share the same base sequences, but single nucleotide polymorphisms create human diversity.
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17
Q

What are the characteristics of bacterial chromosomes?

A
  • circular DNA
  • not associated with proteins
  • single copy of each gene in 1 chromosome
  • 2 identical copies are present briefly after replication, ready for cell division
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18
Q

What are plasmids?

A
  • small extra DNA molecules containing a few genes, not those for basic life processes
  • they are not always replicated at the same time as chromosomes or at the same rate, so there may be multiple copies of plasmids that have not been through cell division
  • they cross species barrier, so the plasmid is absorbed by cells of other species
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19
Q

How is DNA measured using auto radiography?

A
  • cells are grown for 2 generations in a culture containing trusted thymidine, which is linked to deoxyribose, used by ecoli to make nucleotides.
  • trusted thymine = tritium, radioactive isotope of carbon, radioactively labelled DNA produced by replication of E. coli cells.
  • placed on dialysis machine- cell walls digested using lysozyme.
  • they are burst to release DNA on surface- photographic emulsion is applied to the surface of the membrane and it is left in the dark for 2 months to allow tritium to decay
  • it indicates the position of DNA
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20
Q

What are eukaryote chromosomes?

A
  • linear DNA molecules associated with histoine

- composed of DNA and protein, DNA wound around histoines

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21
Q

What are haploid nuclei?

A
  • one chromosome of each pair

- gametes- 1 allele

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22
Q

What are diploid nuclei?

A
  • full pairs of homologous chromosomes

- prevents harmful recessive diseases affecting all with allele

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23
Q

Why can we not interbreed with other species?

A

Because we cannot interbreed with a different number of chromosomes

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24
Q

What are properties of the X chromosome?

A

Large, centromere near centre, contains genes vital to both sexes so is present in both.

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25
Q

What are the properties of the Y chromosomes?

A

Small, centromere near the end, contains less gene, dome the same as x, some only for men. SRY and TFD is a gene on Y that initiates development of male features

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26
Q

What do karyograms show?

A
  • shows chromosomes as homologous pairs, decreasing in length
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27
Q

How do karyograms work?

A
  • chromosomes are stained in metaphase to give the clearest image
  • the dividing cell is placed on a microscope slide, a cover slip is placed over, the cell is burst and the chromosomes spread across the slide and a micrograph is taken
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28
Q

How can we identify Down syndrome?

A

A karyotype shows chromosome abnormalities. A sample can be taken from foetal cells. If 3 copies of chromosome 21 are present, child has Down syndrome.

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29
Q

How is Down syndrome caused?

A

Non disjunction (failure to separate chromosomes during formation of gametes) in chromosome 21

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30
Q

What are the effects of Down syndrome?

A

Causes hearing, heart, vision, growth and mental issues

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31
Q

How was meiosis discovered?

A

Discovered by dyeing chromatin and a microscope revealed chromosomes dividing in the nuclei

32
Q

What is the initial and final product of meiosis?

A

One diploid nucleus divides to produce 4 haploids

33
Q

How is genetic variation produced in meiosis?

A
  • crossing over of homologous pairs (chiasmata- break at crossing point and rejoin as part of the other molecule, allowing DNA to be mixed within the bivalent)
  • random orientation- either set of sister chromatids can be on either side
  • combination of genes from 2 parents- random assortment
34
Q

What happens in Prophase 1?

A
  • diploid cells’ chromosomes pair up and cross over
  • DNA condenses- supercoiling
  • nuclear membrane breaks down
  • spindles form from micro tubules at opposite sides
35
Q

What happens in metaphase 1?

A
  • homologous pairs line up at the equator

- spindle fibres attach at centromere

36
Q

What happens in anaphase 1?

A
  • spindle fibres shorten, pulling chromosomes to opposite sides
  • each pole has 1 member of each pair (haploid on each side)
37
Q

What happens in telophase 1?

A
  • spindle breaks down
  • nuclear membrane reforms
  • cytokinesis and 2 resulting cells are haploid
38
Q

What happens in prophase 2?

A
  • nuclear membrane breaks down
  • new spindle forms
  • chromosomes condense and becomes visible
39
Q

What happens in metaphase 2?

A
  • chromatids arrange at equator

- spindle fibres bind to centromeres

40
Q

What happens in anaphase 2?

A
  • spindle fibres contract and centromeres divide

- chromatids move to opposite poles

41
Q

What happens in telophase 2?

A
  • spindle breaks down
  • nuclear envelopes reform
  • cytokinesis
  • four haploid cells
42
Q

What is non disjunction?

A

When sister chromatids do not separate in meiosis, creating cells with too many or few chromosomes.
In 1st division, 2 cells have an extra chromosome, 2 are missing 1. In 2nd division, 2 cells have the correct number, 1 with too many and one with too few.

43
Q

What genetic diseases are caused by non disjunction?

A
  • with an extra chromosome- Down syndrome in chromosome 21

- with a missing chromosome- turners syndrome (single X chromosome)

44
Q

What happens in amniocentesis?

A

Needle in abdomen to withdraw amniocentesis. There is 1% chance of miscarriage.

45
Q

What happens in chronic villus sampling?

A

The vagina is entered to take cells from the chorion. There is 2% chance of miscarriage.

46
Q

What did Mendel do?

A

He crossed pea plants to discover the principles of inheritance

47
Q

What are gametes?

A

Haploid cells that contain 1 allele of each gene

48
Q

How are genes passed on?

A

In gametes- 1 chromosome from each parent, so one allele from each gamete

49
Q

What are zygotes?

A

Fusion of gametes, diploid zygotes with 2 alleles of each gene. They can be homo or heterozygous.

50
Q

What is dominance?

A

Dominant alleles mask the effects of recessive alleles and co-dominant alleles will have joint effects. Dominant allele codes for functioning protein, recessive for non-functioning.

51
Q

Why do we need to know blood groups?

A

To prevent coagulation in transfusion

52
Q

What are the alleles for blood group B?

A

IB IB or Ibi

53
Q

What are the alleles for blood group A?

A

IAIA or IAi

54
Q

What are the alleles for blood group AB?

A

IAIB

55
Q

What are the alleles for blood group O?

A

ii

56
Q

Which blood group alleles are codominant and or recessive?

A

IA and IB are codominant, i is recessive

57
Q

Why are group A and B codominant?

A

Group A has acetyl galactosamine protein added to the red blood cell membrane and group B has galactose. These are not mutually exclusive so group AB has both.

58
Q

Why is group O recessive?

A

It has no protein added

59
Q

What do the proteins in group A and B do?

A

People without group A protein will create anti-A antibodies, people without group B protein will create anti-B antibodies. O creates both, AB neither

60
Q

What is Huntington’s disease?

A

A genetic disease caused by dominant alleles on chromosome 4 (HTT protein producing Huntington protein). It causes degenerative changes in the brain. There is a 20 year life expectancy after first symptoms, but there is a late onset. It is rare.

61
Q

What is cystic fibrosis?

A

A genetic disease that is carried by recessive alleles on chromosome 7, the gene that codes for chloride ion channel for sweat, mucous and digestive juices. The sweat has too much sodium chloride, mucus and digestive juices have too little. Not enough osmosis in the secretions, making them vicious. This, mucus builds up in lungs and digestive juices block pancreatic duct and don’t reach the small intestine.

62
Q

How is colour blindness inherited?

A

It is a recessive disease for which Females are carriers. If they pass the recessive allele to their son, he will be colour blind. Females can be colour blind if both parents pass down recessive alleles. This is more rare, as males only need 1 recessive.

63
Q

How is haemophilia inherited?

A

It is a recessive disease located on the X chromosome. It is the inability to make Factor VIII, a protein involved in blood clotting. There is a 10-year life expectancy if untreated.

64
Q

What are the uses of PCR?

A
  • DNA sequencing
  • DNA profiling
  • diagnosing disease
  • identifying bacteria
65
Q

What happens in a polymerase chain reaction?

A
  1. Sample is obtained and DNA is denatured as it is heated to 95’C for 5 mins, then cooled to 60’C
  2. Primers (short strands of DNA, starting sequence) are annealed to each strand
  3. Free nucleotides and polymerase are added and bond to primers to synthesise complementary strands of DNA with free nucleotides to form 2 copies of each DNA strand.
  4. This is repeated about 25 times
66
Q

What does gel electrophoresis do?

A

Separates large molecules based on size

67
Q

What are the basic principles of gel electrophoresis?

A

DNA has a slight negative charge due to phosphates, so is repelled by the cathode. They are separated and small DNA molecules travel faster due to size.

68
Q

What are the steps in Gel electrophoresis?

A
  1. Tray prepared with comb to create wells
  2. Agarose gel powder is mixed with buffer solution, which is heated until dissolved and then poured into the tray to cool
  3. Tray is placed in electrophoresis chamber, filled with buffer to allow electric current from the electric currents to flow through.
  4. DNA samples are mixed with loading dye- DNA is visible and contains glycerol or sucrose, so becomes heavy
  5. Once the dye marker has moved through the gel, the current is turned off and the gel is removed
  6. Gel matrix acts as a sieve for negatively charged DNA molecules as they move towards the anode
69
Q

How is a paternity test carried out?

A

DNA samples from the mother, child and potential fathers are taken and amplified by PCR and then separated in size order by gel electrophoresis. They are then profiles to see if the fragments of DNA of the child match the mother or father

70
Q

How is genetic modification carried out?

A
  1. Plasmids can be removed freely and cleaved by restriction enzymes, specific to bases of DNA, to make sure they cut out a section in the right place. They leave sticky ends, which are exposed nucleotide bases.
  2. DNA fragments from other organisms are cleaved by restriction enzymes in the same bases.
  3. Pieces can be added to the open plasmid and spliced together with ligase, which forms hydrogen bonds using base pairing between the sugar phosphate backbone, joined through annealing.
  4. Recombinant plasmids can be inserted into new host cells and then cloned.
71
Q

How does retinol in rice work?

A

Vitamin A1 is essential for immune system, vision and growth. Beta carotene makes retinol, rice contains neither of these, but contains a molecule that makes beta carotene. GM rice contains the gene for beta carotene.

72
Q

What are positives of GM?

A
  • increase crop yields and food production
  • improve health, so there is less dependence on medicines
  • would lead to a decreased use of herbicides and pesticides
  • would be greater nutrition in food
73
Q

What are the negatives of GM?

A
  • people may have allergies to transgenic food
  • it may have little economic benefit
  • it could lead to possible spread of transfers to other species through cross pollination
  • their release into the environment may be irreversible
74
Q

How does cloning work?

A
  1. Somatic cells are removed from desired clone
  2. Ova is produced through super ovulation by FSH
  3. The nucleus of the ovum is removed
  4. The two cells are fused with an electrical pulse
  5. They divide my mitosis to 16 cell stage and then are implanted into the surrogate
75
Q

What are the positives of cloning?

A
  • infertile couples could have own children
  • parents carrying a genetic disease can have healthy children
  • allows for compatible organ transplants
  • new treatment for genetic disease
  • safe and reliable
  • they are not exact duplicates as environmental factors give individuality
76
Q

What are the negatives of cloning?

A
  • may lead to the production of humans - ‘improvement’
  • results in the death of embryos
  • removes individuality
  • playing God

Biology (13 decks)

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