MRCOG Part 1 > Genetics > Flashcards

Genetics Flashcards

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1
Q

What makes up a nucleoside and what makes up a nucleotide?

A

Nucleoside = base + sugar (5C pentose ring)
Nucleotide = base + sugar + phosphate (monomer repeat unit of DNA)

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2
Q

What base differs in RNA compared to DNA?

A

Uracil in RNA, not thymine

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3
Q

What enzyme unwinds parental double helix in DNA replication?

A

Helicase

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4
Q

What enzyme is involved in making a new strand of DNA (DNA replication) from the leading parent strand?
In what direction is the new strand made?

A

DNA polymerase
Made in 5’ –> 3’ direction

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5
Q

On the lagging strand in DNA replication, what direction is the new strand synthesised in?
What are the small segments created called?

A

5’ –> 3
Okazaki fragments

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6
Q

What enzyme binds okazaki fragments together?

A

DNA ligase

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7
Q

What is the term used to make mRNA from DNA?

A

Transcription

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8
Q

What gests spliced out of primary transcript to create mature mRNA?
Introns or Exons?

A

Introns

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9
Q

What enzyme binds to the TATAAAA box on DNA to start the process of transciption?

A

RNA polymerase

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10
Q

What is the termused to describe when mRNA is turned into proteins (aka protein synthesis)?

A

Translation

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11
Q

What is the initiating codon in translation used as the start point?
What does this codon code for?

A

AUG
= methionine

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12
Q

What direction does translation occur in?

A

5’ –> 3’

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13
Q

what is the role of tRNA in translation

A

tRNA contains anticodon to match mRNA and carries the amino acid with it

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14
Q

How many genes does mitochondrial DNA contain?

A

37 genes

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15
Q

DNA is transcribed by what enzyme?

A

DNA directed RNA polymerase

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16
Q

To create a chromosome karyogram, what stage of the cell cycle is it arrested in, in order to see the chromosomes clearly?

A

Metaphase

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17
Q

What is used as a dye when creating a chromosome karyogram?

A

Giemsa staining

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18
Q

What is a balanced translocation?

A

Genetic condition where two chromosomes have swapped pieces, but no genetic material has been lost or gained.

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19
Q

Do people with a balanced translocation in their genetic material have health problems?

A

Usually not as they still have correct amount of genetic material, although the arrangement is unusual.
However, can cause health problems in children as there is a risk of passing on an unbalanced translocation with a loss or extra amount of genetic material

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20
Q

What is aneuploidy?

A

Where there is an abnormal number of chromosomes.
e.g. polyploidy (e.g. 69), trisomy (e.g. 47), monosomy (e.g. 45XO)

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21
Q

What is most common cause of aneuploidy?

A

Nondisjunction - failure of homologous chromosomes or sister chromatids to separate properly during cell division (meiosis or mitosis) resulting in daughter cells with abnormal number of chromosomes (aneuploidy)

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22
Q

What is used to arrest WBCs in metaphase to create a Karyogram?

A

colchicine

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23
Q

What is a metacentric centromere?

A

centromere located in middle of chromosome

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24
Q

What is an acrocentric/telocentric centromere?

A

centromere right at the end of chromosome

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25
What is a submetacentric centromere?
off-centre centromere
26
What is recombination?
shuffling of DNA to create new combinations. Primarily occurs during meiosis through 'crossing over'.
27
Another name for Trisomy 18
Edward's syndrome ('E'dwards - 'E'ighteen)
28
Name physical features/conditions associated with Down syndrome
- upward-slanting palpebral fissures - epicanthic folds - Short neck - Small ears - Hypotonia - Single palmar crease - Wide gap between big and 2nd toe - Flattened facial profile - Mental retardation - choroid plexus cyst - congenital cardiac abnormalities - Duodenal atresia - Brushfield spots in eyes
29
Characteristic features of Patau syndrome
- omphalocoele - cleft lip and palate - microcephaly - Holoprosencephaly (forebrain fails to develop into two hemispheres) - post axial polydactyly - Low set ears - rocker-bottom feet "Patau's Polydactyly"
30
characteristic features of Edward's syndrome
- clenched fists with overlapping 2nd and 3rd fingers - rocker bottom feet - small, low-set ears - micrognathia (small jaw) - prominent occiput - severe structural heard defects - low birth weight - narrow palpebral fissures - severe intellectual disability
31
What gestation can combined screening test be offered?
10-14weeks
32
What are the components of combined screening test
NT free hCG PAPPA-A Age
33
What gestation can the quadruple screening test be offered?
14-20 weeks
34
What factors does quadruple test look at?
hCG inhibin-A AFP uE3
35
What risk ratio is CVS or amniocentesis offered
Risk >1:150
36
What gestation can CVS be offered?
11-14wks
37
What gestation can amniocentesis be offered?
>15wks (usually done before 20 weeks)
38
Risk of miscarriage risk with CVS in: 1. singleton pregnancy 2. multiple pregnancy
1. 1 in 200 2. 1 in 100
39
How long does it take to get CVS or amniocentesis results back?
Usually 72hrs (3 days)
40
Risk of miscarriage with amniocentesis
1 in 200
41
What is the most common cause of Down syndrome?
Non-disjunction in 1st meiotic division (accounts for 94% of cases)
42
What are the 2nd and 3rd most common causes of down syndrome
4% - translocation 2% mosaicism
43
What is main risk factor for chromosome non-disjunction?
Increasing maternal age
44
What is the most common chromosomal translocation in humans?
Robertsonian translocation
45
How many chromosomes does a person with Robertsonian translocation usually have? Does this affect them?
Usually have 45 chromosomes (as two acrocentric chromosomes have fused together - usually p arms of chromosome 14 or 21. Can also occur at chromosomes 13, 15, 22) Usually asymptomatic
46
Are offspring of a parent with Robertsonian translocation affected?
Offspring can be: - Normal - Balanced carrier (asymptomatic) - Trisomy 14 (lethal) - Monosomy 14 (lethal) - Trisomy 21 - Monosomy 21 (lethal)
47
Is NIPT possible in multiple pregnancy?
possible for twins but not higher order multiple pregnancy
48
What 4 syndromes does NIPT test for?
Down, Edwards, Patau's, Turner syndrome
49
Who is NIPT offered to?
Those with high risk on combined/quad screening
50
What is NIPT testing for?
Analyses both baby's and mother's cell-free DNA. (cffDNA - cell free fetal DNA - fetal DNA in maternal plasma comes from placenta - makes up around 10-20% of cell free DNA in maternal circulation)
51
How accurate is NIPT?
99% accurate
52
What are the 3 possible results you can get with NIPT?
- Positive - Negative - Inconclusive (4%) - can repeat but may need invasive testing
53
False positives in NIPT may be caused by what?
vanishing twin placental mosaicism ('cell lines' that grow in placenta but not baby) maternal DNA tested
54
False negatives in NIPT can occur becasue of what?
- fetal DNA too low - High Maternal BMI - Placental mosaicism ('cell lines' that grow in placenta and not baby)
55
How long to NIPT results tend to take to come back?
10 days
56
HNPCC (Lynch syndrome) and BRCA1/BRCA2 are inherited by what mode of mendelian inheritance?
Autosomal dominant
57
The most common cause of CAH is deficiency of what? What mode of inheritance is it?
21-PH deficiency Autosomal recessive
58
Which is a more accurate screening test, combined or quadruple tes?
Combined screening test
59
In NIPT, how can you be sure that you are only testing fetal DNA of current pregnancy and not previous pregnancy?
Because cffDNA is cleared from maternal blood around 1hr after delivery.
60
What effect does Down's have on quadruple blood test results?
Decreased AFP Decreased unconjugaed estriol Increaesed hCG Increased inhibin
61
AFP tends to be increased in what cases?
Neural tube defect
62
Earliest appropriate age to perform CVS?
11 weeks
63
Lifetime risk of breast cancer in woman carrrying BRCA1?
60-90%
64
Lifetime risk of breast cancer in woman carrying BRCA2?
45-80%
65
Lifetime risk of ovarian cancer in woman carrying BRCA1?
40-60%
66
Lifetime risk of ovarian cancer in woman carrying BRCA2?
10-30%
67
47XXY is what condition?
Klinefelter's
68
Symptoms of Klinefelter's?
tall stature small testes infertility reduced muscle mass learning difficulties
69
Kallman syndrome karyotype
46XY or 46XX Genetic condition, not chromosomal disorder so normal karyotype.
70
Signs of Kallman syndrome
Delayed or absent puberty (hypogonadotropic hypogonadism) Anosmia (sometimes cleft palate, kidney issues or hearing loss)
71
Karyotype of MRKH syndrome. Signs of MRKH
46XX (normal karyotype) There is a developmental defect due to lack of fusion of the müllerian ducts. The patient will have a uterine remnant and a blind vagina.
72
Which chromosomal abnormality has a known association with severely impaired semen quality?
Microdeletions of the Y chromosome
73
Most common trisomy seen in early miscarriage?
Trisomy 16
74
What type of genetic alteration causes Cri du Chat?
Partial deletion
75
Which two structural rearrangements of genetic material are likely to get passed on to children?
Inversion and Translocation (turn your child upside down and send them away to boarding school)
76
Which gene is faulty in Lynch syndrome?
DNA mismatch repair gene
77
When caused by inheritance, what mode of inheritance is achondroplasia?
Autosomal dominant (If caused by gene mutation tends to be delterious)
78
Mode of inheritance of Duchenne muscular dystrophy and Becker dystrophy
X linked recessive
79
Most common genotype assocaited with complete mole?
46XX (both X chromosomes being paternally derived)
80
Mode of inheritance of tuberous sclerosis?
Autosomal dominant
81
Which parental chromosomal abnormality is associated with recurrent miscarriage?
Robertsonian balanced translocation. Involves rearrangement of genetic material following breakage and re-attachment in another location. There is no loss or gain of genetic material so the person is phenotypically normal. Incidence is 1 in 1000 in the general population.
82
Which alleles code for Rhesus status?
C, D and E
83
3 most common causes of Down's syndrome in order of most common to least common
95% due to non-disjunction in the FIRST meiotic division; 3% unbalanced Robertsonian translocation 1-2% mosaics
84
Which chromosomes tend to have acrocentric centromeres? What are these chromosomes usually involved with?
13, 14, 15, 21, 22 Centromere close to one end Usually involved in balanced translocations
85
Which chromsomes are metacentric?
centromere in middle 1, 3, 16, 19, 20
86
What is most common mode of inheritance of von Willebrand disease?
Autosomal dominant
87
deficiency of what causes phenylketonuria?
phenylalanine hydroxylase
88
glucose-6-phosphate dehydrogenase deficiency follows what mode of inheritance?
X-linked recessive (note female carriers may experience haemolytic crises)
89
Haemophilia A and B caused by deficiency in what coagulation factors?
A - factor VIII deficiency B - factor IX deficiency
90
Mode of inheritance of androgen insensitivity syndrome
X linked recessive
91
Karyotype of someone with androgen insensitivity syndrome
46XY
92
Phenotype of someone with androgen insensitivity syndrome
female but with absent uterus, blind ended vagina and testes in abdomen/inguinal canal
MRCOG Part 1
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