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Principles - Kate > Genetics > Flashcards

Genetics Flashcards

1
Q

what does DNA stand for?

A

deoxyribonucleic acid

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2
Q

what types of bonds are there between the bases in the DNA double helix?

A

hydrogen bonds

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3
Q

what does RNA stand for?

A

ribonucleic acid

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4
Q

what are the main difference between DNA and RNA

A

DNA is double stranded, RNA is single. DNA has a deoxyribose sugar backbone, RNA has a ribose sugar backbone. DNA have thymine and RNA has uracil

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5
Q

what is the DNA helix wound around?

A

proteins called histones that interact with other proteins to make a structure within the nucleus

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6
Q

how is the chromosome structure made?

A

DNA wraps around a highly basic histone octamer and is then coiled further to make the chromosome structure

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7
Q

what does the condensation of DNA do?

A

controls gene function, it is less transcriptionally active

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8
Q

how many chromosomes are in each cell?

A

22 pairs of chromosomes and the sex chromosomes

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9
Q

how are bases added to the leading strand of the unwound double helix?

A

by DNA polymerase in a 5’ to 3’ direction

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10
Q

how are bases added to the lagging strand of the unwound double helix?

A

short stretches of DNA are synthesised (called Okazaki fragments) and then these are joined together by a DNA ligase

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11
Q

what is mitosis?

A

the process of somatic cell division. one parent cell becomes almost two identical daughter cells

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12
Q

what phase is DNA replicated in?

A

S phase

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13
Q

what happens in stage 1 prophase?

A

chromosomes are condense and form part of the mitotic spindle

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14
Q

what happens in stage 2 metaphase?

A

the chromosomes line up in the centre of the dividing cell. microtubules are attached to each chromosome centromere

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15
Q

what happens in stage 3 anaphase?

A

the duplicated chromosomes are separated by contraction of the microtubules

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16
Q

what happens in stage 4 telophase?

A

the chromosomes reach the poles of the cell and the two cells separate (cytokinesis) the chromosomes de-condense and form part of the nucleus once more

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17
Q

what is meiosis?

A

only occurs during gamete production, ensures that genetic variants on the same chromosome segregate independently through the recombination of gametes are haploids with homologous chromosomes

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18
Q

what happens in prophase meiosis I?

A

homologous chromosomes pair and there is a crossing over between the homologous chromatids

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19
Q

what are you left with at the end of meiosis I?

A

two identical daughter cells

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20
Q

what happens in meiosis II?

A

a second round of cell division leaving 4 haploid daughter cells

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21
Q

what three things are chromosomes recognised by?

A

their size, the position of the centromere and their banding pattern

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22
Q

what’s the difference between a metacentric chromosome and a acrocentric chromosome?

A

a metacentric chromosome has the telomere close to the middle, with a shorter ‘p’ arm and longer ‘q’ arm. an acrocentric chromosome has the centromere at one end, with only satellite DNA on the short ‘p’ arm

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23
Q

what does the dark band on a chromosome show when stained?

A

gene poor regions

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24
Q

when is a chromosome compliment said to be balanced?

A

if there is the normal amount of each chromosome (whether the chromosomes are normal or there is a rearrangement)

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25
Q

when is a chromosome compliment said to be unbalanced?

A

if there is extra or missing chromosomal material

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26
Q

what does trisomy 21 cause?

A

Down syndrome, the most common cause is non-disjunction of chromosome 21 at meiosis

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27
Q

what is robertsonian translocation?

A

where two acrocentric chromosomes become joined end to end. the short ‘p’ arms are lost, but do not contain significant genes

28
Q

what is reciprocal translocation?

A

when there has been a swap of genetic material between chromosome arms.

29
Q

what is the risk of a parent who has a balanced reciprocal translocation?

A

high risk of having children with unbalanced chromosomes, causing miscarriage or children with significant developmental disorder

30
Q

what is FISH?

A

Fluorescence in-situ hybridisation is a technique that allows you to look for the presence of a specific chromosomal region. the region is highlighted by hybridisation of a region-specific probe. used to detect chromosomal abnormalities in cancer

31
Q

what is chromosomal microarray?

A

uses binding of patient DNA to specific known DNA fragments on a slide, allowing analysis of chromosomes at a much higher resolution than karyotyping, identifying many polymorphisms can be a problem though, usually only detects unbalanced chromosomes

32
Q

what is stage one of X inactivation?

A

regulation - in women, one X chromosome is inactivated in early embryonic development, usually one in each nucleus is inactivated at random

33
Q

what is stage two of X inactivation?

A

spreading - starts at the Xist gene on one of the two x chromosomes in a cell, expressing a large RNA molecule that coats the chromosome, followed by condensation of the inactive chromosome into heterochromatin, suppressing gene transcription

34
Q

what is stage 3 of X inactivation?

A

maintenance - x inactivation pattern remains constant throughout the life of the cell, and is maintained during cell division. only removes in germ cell formation

35
Q

what happens in transcription?

A

transcription factors bind to a gene promoter, allowing DNA polymerase to target the stretch of DNA, a precursor RNA (Pre-RNA) is synthesised using the DNA strand as a template

36
Q

what happens during splicing?

A

the precursor RNA will include sequences from the axons of the gene (which encode protein) and the introns (the sequence between which do not). splicing occurs to remove the introns and leave the mature mRNA

37
Q

where does splicing occur?

A

in the nucleus

38
Q

what forms a spliceosome?

A

small nuclear ribonucleoproteins (SNRPs) recognised specific RNA sequences including splice acceptor, splice donor and lariat sequence forming a splicesome

39
Q

where does translocation occur?

A

at the ribosome

40
Q

what is the start codon?

A

AUG

41
Q

what are the three stop codon?

A

UGA, UAG, UAU

42
Q

how can DNA be damaged that would require DNA repair?

A

chemical crosslinks, single and double stranded breaks and incorporation of mismatched basis

43
Q

what are some DNA repair pathways?

A

base excision repair, nucleotide excision repair and mismatch repair

44
Q

what does homologous recombination do (HRR)?

A

repairs double stranded breaks in DNA using the other allele as a template, non-homologous end joining joins the broken strands directly and risks joining together of incorrect DNA strands

45
Q

what are polymorphisms?

A

range from single changes in base sequence to large genomic segments over a million bases in size. most single nucleotide polymorphisms have no effect

46
Q

what is mendels law of independent degradation?

A

when at meiosis these polymorphisms segregate independently into the gamete. recombination in Meiosis I ensures this

47
Q

what is parental somatic mosaicism?

A

somatic mosaicism describes the situation where an individual has a proportion of cells with a different genotype. if this is a disease causing mutation that is present in gonadal tissue, an apparently healthy person could have several children with the same genetic disease

48
Q

what is post-zygotic mosaicism?

A

new genetic variations occur during every somatic cell division, but most of these do not affect gene function. it could be said, therefore, that everyone is a somatic mosaic

49
Q

what is the Philadelphia chromosome?

A

a translocation between chromosome 9 and chromosome 22 that activated the ABL oncogene, a major event in the causation of chronic myeloid leukaemia (CML). the drug Imatinib specifically targets the ABL oncogene and is highly specific and effective treatment

50
Q

what mutation play a large role in the formation on cancer?

A

somatic

51
Q

what is next genetic sequencing (NGS)?

A

describes a number of technologies that can sequence large amounts of DNA. these possible technologies make it possible to sequence the entire genome of an individual for an acceptable cost, within a short period of time. sequence a very large number of fragments. fragments are aligned against a reference genome sequence.

52
Q

what is genetic filtering?

A

used to identify pathogenic variant, variants are removed that are unlikely to be disease causing.

53
Q

what is penetrance?

A

the likelihood that a mutation will cause a disease phenotype in an individual

54
Q

what is autosomal dominant? inheritance

A

a single faulty alley is sufficient to cause disease. 50% change of passing it on

55
Q

what is autosomal recessive inheritance?

A

an affected person has two faulty alleles. happens more commonly in consanguineous parents. risk of a child being affected 1 in 4 and half of the children will be carriers of one pathogenic variant

56
Q

what is x linked inheritance?

A

pathogenic variant is found on the X chromosome, a female with one pathogenic allele and one normal allele does not show major clinical feature of the disease, but a male with a single faulty allele will be fully affected

57
Q

what is x linked recessive inheritance?

A

a carrier female can have an unaffected son (1/4) unaffected daughter (1/4) carrier daughter (1/4) or an affected son (1/4). if as affected male has kids, all his daughters will be carriers and all his sons will be unaffected

58
Q

what is mitochondrial inheritance?

A

mitochondrial DNA is only transmitted maternally in the ovum, males and females are equally affected but only an affected mother passes on the condition

59
Q

what is DNA methylation?

A

a mechanism for control of gene expression, an epigenetic modification of DNA, does not change the base sequence. once methylated, passed on to daughter cells at mitosis involving the enzyme DNA methyltransferase 1

60
Q

what does methylation of a gene promoter prevent?

A

gene transcription factors, and indirectly causing deacetylation of histones

61
Q

what is genomic imprinting?

A

when genes are only active in the allele inherited from one parent. paternally imprinted gene is one that is only expressed in the allele inherited from the mother, a maternally imprinted gene is one that is only expressed in the paternally inherited allele. imprinted genes are found in specific chromosomal regions

62
Q

what are genome wide association studies?

A

where the study looks as polymorphisms across the whole genome

63
Q

what are the hallmarks of cancer?

A

sustaining proliferative signalling, evading growth suppressors, avoiding immune destruction, enabling replicative mortality, tumour promoting inflammation, activating invasion and metastasis, inducing angiogenesis, genomic instability, resisting cell death, deregulating cellular energetics

64
Q

what is the two hit hypothesis?

A

a cell may need to lose two copies of a gene for it to progress towards malignancy, in some cases both these arise though somatic mutations, however sometimes one mutation is inherited

65
Q

what is the BRAF mutation?

A

activated BRAF drives the MAP kinase signalling pathway, increasing cell proliferation. hyperactivity of BRAF = abnormal cell growth

66
Q

what is next generation sequencing?

A

can sequence the entire genome, find genetic cause to rare disease, identifies relevant genes to be included in the analysis, clinical and laboratory equipment can then be used to find the single causative pathogenic variant

67
Q

what phenomenon does Huntington’s disease show?

A

anticipation - the trinucleotide repeat mutation can get longer when transmitted at male meiosis, disease onset is usually in adult life

Principles - Kate (10 decks)

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