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Genetics Flashcards

1
Q

where is the information in DNA held?

A

it is held in the sequence of the bases which are held on a sugar phosphate backbone

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2
Q

Thymine pairs with

A

adenine

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3
Q

guanine pairs with

A

cytosine

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4
Q

DNA is wound into a chromosome by..?

A

Wrapping around histone proteins

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5
Q

what phase of the cell cycle does DNA replication happen?

A

S phase

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6
Q

why might DNA be damaged?

A

the DNA strand breaks, there is chemical cross linking or there is a mismatched base

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7
Q

how can DNA damage be fixed?

A

by repair mechanisms

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8
Q

What happens when there are defects in the repair mechanisms?

A

disease

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9
Q

during mitosis, one diploid parent cell turns into…

A

two identical diploid daughter cells

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10
Q

during meiosis, one diploid parent cell becomes…

A

4 haploid daughter cell (one of each chromosome to each cell)

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11
Q

when does meiosis occur?

A

in gamete formation

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12
Q

what is crossing over?

A

Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis, which results in new allelic combinations in the daughter cells.

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13
Q

how does a gene go from DNA to mRNA

A

transcription and splicing

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14
Q

how does a gene go from mRNA to protein

A

translation

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15
Q

what is the amount of protein produced determined by? 4 answers

A
  • rate of transcription
  • rate of splicing to mRNA
  • half life of mRNA
  • rate of processing of polypeptide
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16
Q

what can 3 bases encode for?

A

1 amino acid or a stop

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17
Q

how is mRNA produced from DNA? Two steps

A

DNA is transcribed to pre mRNA and then pre mRNA is spliced to mRNA

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18
Q

what is polymorphism?

A

a variation in the human genome that has a population frequency greater than 1% or a variation that does not cause a disease in its own right

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19
Q

what is a mutation?

A

a gene change that causes a genetic disorder

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20
Q

why does variation happen?

A

DNA replication is not perfect

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21
Q

what three things allow a chromosome to be recognised?

A

banding pattern with specific stains, length and position of centromere

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22
Q

what arm on the chromosome doesn’t really matter?

A

the short arm

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23
Q

what is the balanced chromosome rearrangement?

A

all the chromosomal material is present

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24
Q

what is the unbalanced chromosome rearrangement?

A

extra or missing chromosomal material

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25
term for whole or missing chromosome ?
aneuploidy
26
term for rearrangement of chromosomes?
translocation
27
large chromosomal imbalance results in?
a higher chance of miscarriage
28
notation for male down syndrome
47XY + 21
29
translocation that has a high chance of miscarriage
trisomy 14
30
what is the name of the condition trisomy 18?
Edwards syndrome
31
notation for Edwards syndrome male
47 XY + 18
32
why is X chromosome aneuploidy better tolerated?
because of X inactivation
33
what is X inactivation?
the random process of one female X chromosome inactivating
34
result of reciprocal translocations
50% will have normal chromosomes or balanced translocation but the other 50% will miscarriage or have a dysmorphic delayed child
35
what do reciprocal translocations have to survive?
meiosis
36
effects of large translocation
large risk of miscarriage and small risk of a dysmorphic delayed child
37
effects of a small translocation
small risk of miscarriage but large risk in a having a dysmorphic delayed child
38
how many bases is too small to see?
5 million
39
cheapest quickest and most sensitive way to count chromosomes?
molecular techniques - no longer FISH
40
newest test available for looking at chromosomes?
Array CGH | array genomic hybridisation
41
benefits of array CGH
allows detection of any size chromosome imbalances
42
what does array CGH not detect?
balanced rearrangements
43
what could chromosome changes do?
activate an oncogene or delete a tumour suppressor
44
what is an oncogene?
a gene which in certain circumstances can transform a cell into a tumour cell
45
what type of analysis do you use to detect chromosome deletions/duplications for balanced rearrangements?
aCGH
46
what is PCR?
a process that allows us to select a short stretch of the genome and amplify it
47
how much of the genome is axons?
only 2-3%
48
what does the rest of the genome do that isn't an exon?
regulate genes, space genes out, insulate genes from promotors and add genes
49
what carries genes?
chromsomes
50
when can mutations arise during cell division?
at any point in the human life cycle
51
a genetic change that contributes to cancer
somatic mosaicism for a chromosomal abnormality
52
what does NGS stand for
Next generation sequencing
53
what does NGS allow?
large scale sequencing cheaply- whole exam or whole genome
54
how many base pairs are on the human genome?
about 3 billion
55
what is a mutation?
a genetic variation that causes a disease
56
what is a polymorphism?
a genetic variation that is prevalent in the population and not, in itself, disease causing
57
what does a promotor mutation result in?
no, or reduced transcription/translation
58
result of a base change
it alters the amino acid sequence therefore a different or non-functioning protein is produced
59
what is the wild type?
the normal DNA sequence
60
name for how to describe a mutation
standard nomenclature
61
what does p. mean?
the change in the peptide (protein) sequence (letters)
62
what does c. mean?
the change in the mature mRNA sequence (amino acid names)
63
standard nomenclature for a stop
*
64
c. for deleting a single base and frameshift (the sixth one and its an A)
c.6delA
65
what is a trinucleotide repeat expansion?
replication of a trinucleotide
66
how many polymorphisms are there?
about 3 billion (changes from the 'normal'
67
any variant in the wild type may be?
- a mutation - a variant of uncertain significance - a polymorphism
68
what is penetrance?
the likelihood of having a disease if you have a gene mutation
69
penetrance in autosomal dominance?
100%
70
what generations is an autosomal dominant disease seen in?
all generations
71
what causes autosomal recessive diseases?
2 faulty copies of gene to cause disease
72
what generations is an autosomal recessive disease seen in?
only one generation
73
x linked disease example
haemophilia
74
where does the X linked recessive gene lie?
gene fault lies on the X chromosome
75
who carries the x linked recessive mutation? will they show features of the disease?
Females are carriers and do not show major features of the disease
76
for an affected X-linked female, how will her offspring be affected?
half of the male children will be affected and half of the females will be carriers
77
for an affected X-linked male, how will his offspring be affected?
all of his male children will be normal and all of female children will be carriers
78
why might a female carrier show mild features of an x-linked disease?
x inactivation, half the cells have the working gene on average
79
what does SNP stand for
single nucleotide polymorphisms
80
effects of most SNPs
no effect
81
what does CNVs stand for?
copy number variations
82
what are CNVs?
extra or missing stretches of DNA
83
in Mendelian disorders, they have a ........ penetrance and a ...... environmental contribution
high penetrance and a small environmental contribution
84
in multifactorial disease, a genetic change is ........, penetrance for any one mutation is .....
just another risk factor | mutation is low

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