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EMS > Theme 2 - Genetic and environmental cause of disease: Part 2 > Flashcards

Theme 2 - Genetic and environmental cause of disease: Part 2 Flashcards

1
Q

What is aneuploidy?

A

Additional or less chromosomes deviating from the normal haploid number
e.g trisomy, monosomy

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2
Q

What is polyploidy?

A

More than two paired sets of chromosomes

e.g triploidy, tetraploidy

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3
Q

What is mosaicism?

A

when a person has 2 or more genetically different populations of cells
-one is genetically normal, one is genetically abnormal

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4
Q

What is non-disjunction?

A
  • meiotic errors

- Failure of chromosome or chromatid separation

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5
Q

Could fetal monosomy be viable?

A

Fetal monosomy is lethal and fatal trisomy could be viable

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6
Q

Which 3 trisomy are viable?

A

Trisomy 21 - downs syndrome
Trisomy 13 - patau syndrome
Trisomy 18 - Edwards syndrome

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7
Q

Why are only these 3 trisomys viable?

A

Because there are fewer genes on these chromosomes than others

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8
Q

Which syndromes are associated with sex chromosome aneuploidy?

A
  1. Turner syndrome (45, X)

2. Klinefelter syndrome (47, XXY)

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9
Q

What are two types of cytogenic chromosome analysis?

A

G-banding and FISH (FISH has much higher resolution than G-banding)

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10
Q

What are three types of DNA-based methods?

A

Chromosomal microarray, QF-PCR, WES

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11
Q

There is a deletion of which chromosome in DiGeorge syndrome?

A

22q11.2

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12
Q

Why is chromosomal microarray better than karyotyping?

A
  • only needs DNA, not live cells
  • higher resoltuion
  • accurate location & size of imbalances
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13
Q

What is pericentric inversion?

A

If the two break points are on different chromosome arms

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14
Q

What is paracentric inversion?

A

Both breakpoints are on the same arm

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15
Q

Why can’t you always use DNA based methods?

A

Cytogenic analysis is still needed for genome rearrangements e.g translocations

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16
Q

What is robertsonian translocation?

A
  • Whole arm fusion
  • a type of translocation in which two acrocentric chromosomes are fused
  • where a certain type of chromosome becomes attached to another
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17
Q

What is Williams syndrome?

A

microdeletion of chromosome 7

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18
Q

What does Acrocentric mean?

A

having the centromere situated so that one chromosomal arm is much shorter than the other

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19
Q

What is non-disjunction?

A

The failure of one or more pairs of homologous chromosomes to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei

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20
Q

What is mosaicism?

A

involves the presence of two or more populations of cells with different genotypes

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21
Q

What is pallister Killian syndrome?

A
  • mosaic tetrasomy 12p (isochromosome) - this means chromosome 12 is made up of two p arms
  • intellectual deficit, seizures, dysmorphic features, skin pigmentation
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22
Q

What is an isochromosome?

A

A chromosome with two identical arms. Normal chromosomes have one long (q) arm and one short (p) arm, but isochromosomes have either two q arms or two p arms.

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23
Q

What is a population/genetic bottleneck?

A

a sharp reduction in the size of a population due to environmental events e.g famine, earthquakes, genocide

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24
Q

What is a somatic mutation?

A
  • Occur in nongermline tissues

- cannot be inherited

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25
Q

What is a germline mutation?

A
  • present in egg or sperm

- can be inherited

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26
Q

What are the two classes of variation?

A
  1. Variation that does not alter the DNA content (number of nucleotides is unchanged) e.g single nucleotide replacements
  2. variation that results in a net loss or gain of DNA sequence - can be large (whole chromosome) or small (single nucleotide)
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27
Q

What is an SNP?

A

DNA sequence variation occurring when a single nucleotide - A,T,C or G - in the genome differs between members of a species (or between paired chromosomes in an individual)

28
Q

What is a missense mutation?

A

an amino acid change

29
Q

What is a nonsense mutation?

A

change of amino acid to a stop codon

30
Q

What is a silent mutation?

A

the codon for an amino acid is changed, but the same amino acid is still coded for

31
Q

What is an example of negative selection of a gene variant?

A

Mutations causing late onset disease can be more frequent whereas mutations that compromise early development or neonatal health will not persist in a population

32
Q

What is an example of positive selection of a gene variant?

A

the inverse correlation between skin pigmentation and latitude is thought to have been shaped by selective pressures favouring lighter skin to facilitate vitamin D synthesis in regions far from the equator

33
Q

What is allelic heterogeneity? give example

A

Different pathogenic variants in a single gene - multiple different phenotypes
example - mutation in FGFR3 (fibroblast growth factor receptor 3) can cause many different phenotypes e.g achondroplasia

34
Q

What is locus heterogeneity?

A

mutations at multiple genomic loci are capable of producing the same phenotype (ie. a single trait, pattern of traits, or disorder), and each individual mutation is sufficient to cause the specific phenotype independently.

35
Q

How can abnormalities in chromosomes arise?

How can abnormalities in genes arise?

A 
Chromosome problems:
-chromosome number
-chromosome structure
-missing or extra chromosomal material
Gene problems:
-point mutations
-single or multi-exon deletions/insertions
-repeat expansions
36
Q

What is a conservative missense?

A

Amino acid substitution within same group e.g alanine and leucine

37
Q

What is a non-conservative missense?

A

Amino acid substitution to one in a different group e.g phenylalanine and glutamine

38
Q

What is the start codon and what does it code for?

A

AUG - codes for methionine

39
Q

What are canonical splicing variants?

A

variants that occurs at the boundary of an exon and an intron (canonical splice site) and therefore impact splicing

40
Q

What is achondroplasia?

A

increased activity of FGFR3, severely limiting bone growth e.g dwarfism

41
Q

What is the normal function of FGFR3?

A

Slow down the formation of bone by inhibiting the proliferation of chondrocytes

42
Q

How do we classify variants?

A 
class 1: benign
class 2: likely benign
class 3: variant of uncertain significance
class 4: likely pathogenic
class 5: pathogenic
43
Q

What is CHARGE syndrome?

A 
C-coloboma
H- heart defect
C - choanal atresia
R- retarded growth and development
G- genital hypoplasia
E- ear anomalies
44
Q

What type of mutations can cause Duchenne muscular dystrophy?

A

large deletions - one or more exons are missing from the dystrophin gene
large duplications - one or more axons have extra copies in the dystrophin gene

45
Q

Which two recurrent deletion syndromes are due to unequal crossing over?

A
  • williams syndrome

- Di George syndrome

46
Q

Why does Huntington’s show anticipation?

A

Bigger expansions throughout generations - earlier age of onset

47
Q

What are monozygotic twins?

A

identical

48
Q

What are dizygotic twins?

A

non-identical twins

49
Q

How can you prevent NTDs?

A

maternal folic acid supplementation

50
Q

What is the neurology behind Alzheimers?

A

shrinkage of brain, tangles of B-amyloid protein in nerve fibres of hippocampus

51
Q

What are genetic association studies?

A

they seek to relate variation in human DNA sequence with a disease or trait

52
Q

What is the p level?

A

the probability of rejecting the null hypothesis given that it is true - often set at 0.05

53
Q

what is linkage disequilibrium?

A

non-random association of alleles at different loci in a given population

54
Q

What is GWAS?

A
  • genome wide association study
  • examination of all or most of the genes of different individuals of a particular species see how much the genes vary from individual to individual
55
Q

What is hardy Weinberg equilibrium (HWE)

A

The situation where allele and genotype frequencies in a population remain constant from generation to generation in the absence of other evolutionary influences

56
Q

What is minor allele frequency?

A

the frequency of the less common variant in a population

57
Q

Why is BRCA1/2 gene testing advantageous?

A
  • women with breast cancer may have better responses to cancer treatments that are specifically designed for BRCA positive patients e.g cisplatin
  • can encourage prophylactic surgery (removes ovaries)
  • preventative mastectomy
58
Q

How and when can you diagnose a genetic disorder in an infant?

A

amniocentesis - 17 weeks
chorionic villus sampling - 11 weeks
NIPD - 10 weeks

59
Q

What is gene therapy?

A
  • the use of genetic material (DNA, RNA) as a medicine

- introduction of functional genes, in the form of DNA, to replace mutated genes

60
Q

What is preventative medicine?

A

information about a persons genotype used to tailor medical care to prevent disease

61
Q

What are cytochrome P450 oxidases and what do they do?

A
  • multigene family of enzymes found mostly in liver
  • responsible for the metabolic elimination of most drugs currently used
  • important for converting pro-drugs to their active forms
62
Q

How does array CHG work?

A
  • DNA is extracted and fluroescently labelled
  • co-hybridise normal reference DNA and test genomic DNA
  • both DNAs compete to combine to the same sites
  • signal is analysed by computer
  • if signal is less than control its a loss of a chromosome and if its more than control its a gain of a chromosome
63
Q

What is FISH?

A

A cytogenetic technique that uses a DNA probe to examine a single locus

64
Q

Where is the chromosomal translocation that causes wolf Hirschhorn syndrome?

A

unbalanced t(4;8) translocation
top region of chromosomes. 4 has replaced top region of chr 8
T(4,8) is a highly recombinant region

65
Q

What is hypotonia?

A

low muscle tone

66
Q

What are the features of wolf Hirschhorn syndrome?

A
  • delayed growth and development
  • charachteristic facial appearance
  • intellectual disability

EMS (16 decks)

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