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Cambridge Bio Content > Genetics + Inheritance > Flashcards

Genetics + Inheritance Flashcards

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1
Q

What do genes in DNA control?

A

Genes control the exact protein structure, which affects function. Chromosomes contain several genes, meaning they code for several proteins.

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2
Q

What are alleles?

A

Alleles contain slightly different nucleotide sequences but have the same gene locus.

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3
Q

What is a codon?

A

A codon is a triplet code that codes for a specific amino acid or the start and end of a polypeptide sequence.

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4
Q

What is meant by a ‘non-overlapping code’ in DNA?

A

In a non-overlapping code, the DNA is read correctly, and a point mutation affects only one amino acid (e.g., sickle cell anemia).

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5
Q

What does ‘degenerate’ mean in relation to the genetic code?

A

‘Degenerate’ means multiple codons code for the same amino acid. Some mutations may not show any effects.

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6
Q

What is the universality of the genetic code?

A

The genetic code is universal, meaning genetic information is transferable between species.

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7
Q

What are totipotent cells and when do they appear? What are the uses of totipotent stem cells?

A

Totipotent cells appear 3-4 days post-fertilization. They can divide and differentiate to produce any type of body cell. Embryonic stem cells are only present up to 16 days post-fertilization which only translate specific sections of DNA to become specialised. Present in embryo and placenta. Uses: transplants or therapies for leukaemia- tightly regulated.

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8
Q

What are pluripotent stem cells and when do they appear?

A

Pluripotent stem cells appear 5 days post-fertilization. They can divide to form any cell type in the embryo but not the placenta.

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9
Q

What are induced pluripotent stem cells?

A

Induced pluripotent stem cells are formed from adult somatic cells by using transcription factors to dedifferentiate them back into pluripotent stem cells. These can be used in therapies but may cause tumor formation as genes which control cell regulation may be switched on. Uses: islet cells producing insulin, nerve cells reversing paralysis, treatment of macular degeneration in retina, replacing neurone in Alzheimer’s

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10
Q

What are multipotent stem cells?

A

Multipotent stem cells can divide multiple times but can only produce certain cell types, such as blood cells in bone marrow (erythrocytes as they have no nucleus to divide or neutrophils), or cells in the skin, gut, heart, and brain. Can use stem cell therapy to repair damaged tissues: leukaemia, skin burns but need to be matched for antigens in blood and tissue type.

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11
Q

What are unipotent stem cells?

A

Unipotent stem cells can only divide into cells of their own type, such as cardiac monocytes and neurons.

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12
Q

What is a structural gene?

A

A structural gene codes for a functional protein.

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13
Q

What is a regulatory gene?

A

A regulatory gene codes for proteins that control the expression of structural genes. (Could be several at once)

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14
Q

How do transcription factors regulate gene expression? How does oestrogen do this?

A

Transcription factors bind to the promoter region of genes, changing the rate of transcription. For example, oestrogen passes through the PLB and binds to receptors on the nucleus which change shape and detach from the nucleus to attach to regulatory genes and allow RNA polymerase to bind to others increasing the rate of transcription.

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15
Q

What is post-transcriptional regulation?

A

Post-transcriptional regulation involves the production of pre-mRNA and splicing to remove non-coding sections.

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16
Q

What is post-translational regulation?

A

Post-translational regulation involves modifications to proteins in the Golgi apparatus or cytosol by the activation of proteins kinases by cyclic AMP which can act as precursor molecules. Glycogen phosphorylase releases glucose in muscle cells activated by cAMP to expose its active site.

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17
Q

What are homeobox genes?

A

Homeobox genes control which genes are switched on and off using transcription factors. They form the basic pattern of the body (head to tail axis) and control segmentation (e.g., where organs are located). These sequences are highly conserved going back in evolutionary time as the shape of DNA regions are the same in all organisms so there is a strong selection pressure against mutations in homeobox genes are they would be killed in natural selection.

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18
Q

What are Hox genes?

A

Hox genes determine the identity of the embryonic body axis (e.g., head to tail). Humans have four Hox clusters located on different chromosomes. Correspond to linear order based on which regions of the body they effect.

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19
Q

What happens during apoptosis?

A

During apoptosis, chromosomes condense, the nuclear envelope breaks down, vesicles containing hydrolytic enzymes are produced, and phagocytosis occurs. This can regulate cell development eg breaking down cells between hand digits in embryo

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20
Q

What internal stimuli can trigger apoptosis?

A

Internal stimuli include genetic damage, RNA decay, biochemical changes leading to cell injury, and production of cyclin D, which drives the G1/S phase transition.

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21
Q

What external stimuli can trigger apoptosis?

A

External stimuli include cytokines from the immune system, growth factors, hormones, pathogens, UV light, and pollutants.

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22
Q

What is epigenetics?

A

Epigenetics involves changes in gene function without changing the base sequence by chemical modifications of DNA, affecting how tightly DNA is wound around histones which may cause genes to be switched off if too tight as promoter regions are hidden from transcription factors and RNA polymerase

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23
Q

What is the epigenome?

A

The epigenome is heritable but can undergo changes due to environmental factors like smoking or stress or internal cell signalling

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24
Q

What is acetylation in epigenetics?

A

Acetylation adds acetyl groups to lysine on histone proteins which causes a positive ion to be removed from the lysine and prevents an ionic bond between the negative sugar phosphate backbone to be formed, making the DNA less tightly wound and stimulating gene expression. This process is reversible and therefore it can vary with age.

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25
Q

What is methylation in epigenetics?

A

Methylation adds methyl groups to cytosine bases in sequences that contain lots of cytosine and guanine bases, making the DNA more tightly wound due to them attracting histone proteins and inhibiting transcription.

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26
Q

What is epigenetic imprinting?

A

Epigenetic imprinting involves methylation of DNA during oogenesis or spermatogenesis. It is reversible and can lead to disorders like Prader-Willi syndrome. This is because maternal imprints will become paternal imprints when inherited by a male. Prader-Willi syndrome which is a metabolic disorder causing difficulty eating and excessive feeding in infancy. Caused by silencing of allele on C15. If mother is a carrier individuals will not develop disease because this allele is always inactive but if father is a carrier individual will develop syndrome

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27
Q

How can epigenetics be used in cancer treatment?

A

Methyl groups can be removed from DNA to allow tumor suppressor genes to be expressed, and acetyl groups can be removed from histones to inhibit oncogenes. To regulate the cell cycle and trigger apoptosis.

28
Q

What is RNA interference?

A

RNA interference is a post-transcriptional modification:
- Double stranded RNA (dsRNA) is produced by RNA-dependent RNA polymerases (RDRs)
- dsRNA is hydrolysed into smaller fragments, roughly 23 nucleotides long, called small interfering RNAs (siRNAs)
- In the cytoplasm, siRNAs bind to protein complexes which use energy from ATP to separate the two strands of the siRNA
- This exposes the nucleotide bases so they are able to pair with bases from an mRNA molecule
- Once the target mRNA leaves the nucleus and enters the cytoplasm, single-stranded siRNA binds to the target mRNA through complementary base pairing
- The mRNA molecule is cut into fragments by the enzyme/protein complex associated with the siRNA
- Cut mRNA cannot be translated and therefore will not produce proteins
- After the target mRNA has been cut up into fragments, the fragments are broken down into RNA nucleotides by enzymes

29
Q

How is RNA interference used therapeutically?

A

RNA interference can prevent viral genetic replication and the expression of oncogenes.

30
Q

How do tumors cause damage?

A

Tumors can damage organs, cause blockages, or put pressure on surrounding tissues.

31
Q

What is the difference between malignant and benign tumors?

A

Malignant tumors grow rapidly, can metastasise and secrete chemicals which allows angiogenesis where blood can supply oxygen and growth factors, and may be caused by carcinogens and are also likely to recur. Benign tumors grow slowly, do not metastasize, and may be caused by injury or infection, diet eg polyps on ovaries, viral warts or brain tumours.

32
Q

How can overproduction of estrogen cause breast cancer? How can it be treated?

A

Overproduction of estrogen can act as a transcription factor and increase the expression of oncogenes, leading to breast tumors. A drug tamoxifen acts as a competitive inhibitor to oestrogen receptors so that these oncogenes are not expressed.

33
Q

What is recombinant DNA?

A

Recombinant DNA involves combining nucleotides from different organisms since the genetic code and protein synthesis process are universal.

34
Q

What are genetically modified organisms (GMOs)?

A

GMOs contain genetic material from another organism.

35
Q

What is the process to produce genetically modified organisms?

A

The process involves identifying the desired DNA fragment, isolating it, multiplying it (via PCR), transferring it into an organism using vectors (plasmids, viruses or liposomes), and identifying cells with the new DNA fragment using a marker which is then cloned.

36
Q

What is the process of DNA probing and hybridization?

A

DNA is extracted, amplified using PCR, and fragmented with restriction enzymes. The fragments are separated using gel electrophoresis and bands of DNA are transferred to a nylon membrane. DNA is then made single stranded by breaking hydrogen bonds. Probes (complementary to DNA) are used to identify harmful alleles by binding to the target DNA, and the location of bound DNA is detected by washing the membrane.

37
Q

What is genetic screening used for?

A

Genetic screening identifies genetic disorders, such as BRCA1 and BRCA2 for breast cancer, Huntingtons disease and CFTR mutations for cystic fibrosis which means that chloride ions aren’t transported into cells and therefore water doesn’t move out.

38
Q

What is genetic fingerprinting?

A

Genetic fingerprinting uses gel electrophoresis to analyze DNA but must be compared to a reference sample, often used in forensics and to determine familial relationships and identify risk to the next generation of a disease.

39
Q

What is codominance?

A

Codominance occurs when two dominant alleles are both expressed, such as in blood type AB, where both A and B are dominant. (O is recessive)

40
Q

What are sex-linked genes?

A

Sex-linked genes are found on chromosomes that are not present on the other sex chromosome. Most sex-linked genes are X-linked.

41
Q

What is autosomal linkage?

A

Autosomal linkage occurs when two or more genes do not assort independently in meiosis, meaning they stay together in the original parental combination.

42
Q

What causes phenotypic variation?

A

Phenotypic variation results from both genetics and environmental factors.

43
Q

What is epistasis?

A

Epistasis occurs when two genes on different chromosomes affect the same characteristic, and the combination of alleles defines the phenotype. This is detected by a deviation in standard phenotypic ratios

44
Q

What is the Hardy-Weinberg equilibrium equation?

A

The Hardy-Weinberg equation is ( p + q = 1 ) for allele frequencies, and ( p^2 + 2pq + q^2 = 1 ) for genotype frequencies.

45
Q

What conditions must be met for Hardy-Weinberg equilibrium?

A

Conditions include sexual reproduction, random mating, large population, no migration, mutation, or separation, and equal allele frequencies in both sexes, organisms must be diploid.

46
Q

How is RNA analysis conducted?

A

compare production of RNA between heathy cell and diseased cell to determine which genes are being over expressed and target with therapies eg cancer

47
Q

How is an unknown cell signalling pathway investigated?

A

genes expression controlled by signalling pathway due to conformational changes in enzymes and proteins so ATP can be used to phosphorylate these proteins and enter signalling pathway to activate a protein

48
Q

What is genome sequencing? What is the human genome project?

A

DNA samples collected from range of individuals from species to account for mutations or alterations to produce a reference genome
Human genome project: international collaboration to sequence genes on different chromosomes. Now sequencing proteome and epigenome. Specific genes can be linked to inherited diseases, cancers and Alzeihmers

49
Q

How is genome sequencing useful in vaccine development?

A

Used to identify certain genes in malarial parasite which show large amounts of variation showing they are under selection pressure and may code for antigens or resistance which can be useful in vaccine development

50
Q

How is automated DNA sequencing conducted?

A

Short single strand of DNA inserted into vector (primer annealed to start of recombinant DNA)
DNA polymerase added during incubation period so DNA replication begins but also contains dideoxyribose nucleotides which can be inserted by chance and terminate replication
Complementary chains of varying length are produced and bases labelled with fluorescent dye of different colour
After incubation period dideoxyribose strand removed and separated according to size using electrophoresis in capillary tube
Flouresce in laser light and analysis sent to computer

51
Q

How is manual DNA sequencing conducted?

A

Use of gel electrophoresis by placing in separate wells and letting it run
Labelled with radioactivity
Separate run required for each pure dideoxyribose nucleotide of each base
Produces autoradiograph- ban which has mover the furthest is the smallest fragment so is the first base in the sequence and it continues as such

52
Q

What other molecules are used for genetic modification?

A

Enzymes (restriction endonucleases, ligase and reverse transcriptase)
Vectors - used to deliver DNA fragments into a cell (eg. plasmids, viruses and liposomes)
Markers - genes that code for identifiable substances that can be tracked (eg. GFP - green fluorescent protein which fluoresces under UV light or GUS - β-glucuronidase enzyme which transforms colourless or non-fluorescent substrates into products that are coloured or fluorescent)

53
Q

Describe the process of DNA fragmenting?

A

Extraction: specific restriction endonuclease enzymes (released by bacteria to destroy viral genetic material of bacteriophages) binds to specific sections of DNA and separates strands cutting them to give sticky ends or blunt ends. Sticky ends desired as other areas of DNA where enzyme has acted can form hydrogen bonds with complementary base pairs. Unknown restriction enzyme can be identified by observing restriction fragments in gel electrophoresis.
mRNA and reverse transcriptase: mRNA created by desired genes can be used with reverse transcriptase to produce complementary DNA strand and DNA polymerase then used to create double stranded DNA. Preferred as mRNA does not contain introns so specific genes can be analysed eg Beta cells in pancreas for insulin production
Artificial synthesis using proteome sequencing to generate nucleotide sequences and insert into vectors eg plasmids. Used to generate new DNA for vaccination and even new bacterial DNA

54
Q

What is the polymerase chain reaction and what does it require?

A

Used for DNA profiling, genetic engineering and DNA amplification in vitro
PCR instrument provides optimum temperature and controls time spent at each stage
Requires:
Target DNA/RNA
Primer: identifies to DNA polymerase where to begin replication, single stranded DNA complementary to 3 prime end
DNA polymerase
Free nucleotides
Buffer solution: provide optimum pH

55
Q

Describe the steps of the polymerase chain reaction?

A

Denaturation – the double-stranded DNA is heated to 95°C which breaks the hydrogen bonds that bond the two DNA strands together
Annealing – the temperature is decreased to between 50 - 60°C so that primers (forward and reverse ones) can anneal to the ends of the single strands of DNA
Elongation / Extension – the temperature is increased to 72°C for at least a minute, as this is the optimum temperature for Taq polymerase to build the complementary strands of DNA to produce the new identical double-stranded DNA molecules

56
Q

What is in vivo cloning?

A

Extraction of DNA using recombinant DNA methods
Endonucleases and ligase used to insert into plasmids in bacterial vector
Markers used to identify which bacterias have taken up desired genes- others are destroyed
Remaining bacteria cultured

57
Q

What is gene therapy and how can it be done ex vivo/ in vivo?

A

Can replace insert or inactivate faulty gene has been done on somatic body cells so it is not inheritable but effects short lives
Can be ex vivo: inserted into virus vector outside the body then replicated cell injected back in via vein or In vivo: viral vector inserted into body

58
Q

What are recombinant proteins? and give examples of their uses

A

Produced in eukaryotic cells to be modified in golgi apparatus which prokaryotic cells dont have
Insulin: inserted into bacterial plasmids in escherichia coli and insulin produced purified after the whole process. Fewer chance of rejection and intolerance to animal insulin
Factor VIII: treatment for haemophilia. Kidney and ovary hamster cells engineered to produce it and can be purified into an injection. Less risk of transmitting disease

59
Q

Explain gene therapy for SCID

A

Severe combined immunodeficiency (SCID) is caused by the body’s inability to produce adenosine deaminase (ADA), an enzyme that is key to the functioning of the immune system. Without this enzyme, children can die from common infections
To treat SCID scientists have used ex vivo somatic gene therapy. Virus transfers a normal allele for ADA into T-lymphocytes removed from the patient then returned via an injection
Not a permanent cure as the T-lymphocytes are replaced by the body over time- requires regular transfusions
Originally retroviruses were used as the vectors, however these viruses insert their genes randomly into a host’s genome which means they could insert the gene into another gene or into a regulatory sequence of a gene (which could result in cancer)
Initial treatments did cause cases of leukaemia in children, so researchers switched to using lentiviruses or adeno-associated viruses as vectors. Lentiviruses also randomly insert their genes into the host genome however they can be modified to not replicate, whereas adeno-associated viruses do not insert their genes into the host genome. This is an issue with short-lived cells like lymphocytes but has not been a problem when used with longer living cells such as liver cells

60
Q

What is variable number tandem repeats?

A

non coding repeating sequences of DNA that vary in length between individuals. Number inherited from parents so can be used in DNA testing. Distance between recognition sites of restriction enzymes will depend on number of sequences then separated using electrophoresis (separated based on size, mass and net charge)

61
Q

What is synthetic biology?

A

making large changes to a genome to produce a new organism eg antimalarial drug artemisinin and have added genes to improve speed of replication

62
Q

Why does genetic variation occur?

A

Crossing over
Independent assortment
Random fusion of gametes
Mutations

63
Q

How can genotypes be predicted and sex linked conditions be identified?

A

Can use monohybrid and dihybrid crosses to predict genotypes and phenotypes but rely on the fact that genes behave independently of each other- unexpected phenotypic ratio shows that genes are linked
For sex linked genes one sex will be disproportionately affected in pedigree diagrams because males have only one X chromosome they are more likely to present with recessive sex linked condition- males cant be a carrier or pass disease onto sons as they only pass Y chromosome on
Recombinant offspring can be produced where crossing over in meiosis means that linkage can be broken

64
Q

How can you determine whether an individual is homozygous or heterozygous dominant for a characteristic?

A

cross with a homozygous recessive and analyse results
One sex chromosome comes from each parent and male is XY and female is XX

65
Q

How is the Chi squared test conducted and what does it show?

A

Determine if there is a statistically significant difference between observed and expected phenotypes. Compare to a critical value and if the chi squared is greater than or equal to critical value there is statistically significant difference

66
Q

What is continuous variation?

A

eg height: due to genotype and environment-caused by different alleles having small effect on phenotype and different genes may affect the phenotype so additive effect causes this. Polygenes when multiple genes affect one phenotype

67
Q

What is discontinuous variation?

A

Based solely on genotype eg blood group, F8 gene coding for Clotting Factor VIII in haemophilia. Different alleles have large effect on phenotype

Cambridge Bio Content (14 decks)

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