Genetics Flashcards
1
Q
What are the phases of the cell cycle?
A
G1 phase
S phase
G2 phase
M phase
2
Q
What is the M phase
A
Mitosis phase
3
Q
What happens to cells in the G0 phase?
A
Stimulated by growth factor, resulting in activation of transcription factors that lead to the initiation of DNA synthesis, followed by mitosis and cell division.
4
Q
What happens in G1 phase?
A
Chromosomes are prepared for replication.
5
Q
What happens in synthetic phase?
A
46 chromosomes are duplicated into chromatids
6
Q
What happens in interphase?
A
Replication of cellular genetic material and organelles to prepare for next division
7
Q
What is the longest phase in the cell cycle?
A
Interphase
8
Q
Which steps in the cell cycle constitute the interphase?
A
G0
G1
G2
S
9
Q
Stages of mitosis?
A
Prophase
Metaphase
Anaphase
Telophase
10
Q
What happens during prophase?
A
Condensation of chromatin
breakdown of nuclear envelope
spindles at opposite cellular poles
11
Q
What happens during metaphase?
A
Alignment of chromosomes
12
Q
What happens during anaphase?
A
Separation of paired chromosomes
13
Q
What happens during telophase?
A
Chromosomes are packed into distinct new nuclei in emerging daughter cells.
Cytokinesis (division of cytoplasm) also starts
14
Q
What happens in Meiosis 2?
A
Same as normal mitosis
15
Q
What is a acrocentric/submetacentric chromosome?
A
Centromere is at one end, so arms are of unequal length.
16
Q
What is telocentric?
A
When centromere is at tail end of chromosome.
17
Q
What is a holocentric chromosome?
A
Entire length of chromosome acts as centromere.
18
Q
When types of chromosomes are not seen in humans?
A
Telocentric
Holocentric
19
Q
What is an aneuploid cell?
A
When a cell possesses chromosomal numbers different from normal diploid status.
20
Q
What failure results in triploidy/tetraploidy?
A
Non-disjunction - failure of chromosome/chromatid to separate in meiosis
21
Q
Rate of Downs?
A
1:700
22
Q
Prominent findings in Downs?
A
Reduced maternal levels of alpha-fetoprotein
Increased beta-hCG
Increased nuchal fold thickness in fetal USS
23
Q
What is 95% of Downs attributed to?
A
Meiotic nondisjunction of homologous chromosomes,
24
Q
What are 4% of Downs due to?
A
Robertsonian Translocation
25
What characterizes Edwards syndrome?
```
Severe mental retardation
Rocker bottom feet
Low-set eats
Micrognathia (small jaw)
Congenital heart disease
```
26
Frequency of occurrence of Edwards syndrome?
1:8000
27
Which gender is Edwards syndrome more common in?
Three times more common in girls
28
Characteristics of Trisomy 13?
```
Severe mental retardation
Microphthalmia
Microcephaly
Cleft lip/plate
Coloboma eye
Abnormal forebrain structures
Polydactyly
```
29
Rate of occurrence of Patau's?
1:6000
30
Cause of Turners in 80%?
Origin of aneuploidy is from paternal X chromosome, so Turners is of maternal origin
31
Occurrence of Turners?
1:2000 live-born female infants
32
IQ profile of Turners?
Lower than general population by mean of 10 points (nearly one SD) due to reduced performance IQ
Verbal IQ preserved
33
What are the purine nucleic acids in DNA?
Adenine
| Guanine
34
Difference between DNA and RNA?
RNA is single stranded in humans
| DNA is double stranded
35
What is an exon?
Polypeptide coding sequences in DNA
36
Types of sequences in introns?
Satellite
Mini-satellite
Micro-satellite
37
When are introns removed?
ntrons are removed from mRNA before it leaves the nucleus and starts protein synthesis.
38
What is the name of synthesis of RNA from nuclear DNA?
Transcription
| In cell nucleus
39
What is heterogeneous nuclear RNA?
Transcripted RNA which contains junk sequences (introns) that do not code for polypeptides,
40
Where are transfer RNAs synthesized
Synthesized from DNA in nucleus
41
What happens in termination?
Chain termination is signaled by one of three codons; UAA, UGA, UAG
42
What is modification?
Post-translational changes in a protein molecule before it becomes functionally active.
43
Where do modifications take place?
Endoplasmic reticulum
| Golgi bodies
44
Where does protein destruction occur?
Lysosome
45
What is transcriptomic?
Study of mRNA using microchip arrays
46
Define a mutation
Sudden, permanent and heritable change in DNA sequence
47
What is a point mutation?
Single-base alteration in DNA
48
What can lead to point mutations?
Substitution - one base replaced by another
Transition - if purine is replaced by another purine/pyrimidine with pyrimidine
Trans version - purine replaced by pyrimidine and vice versa
49
What happens in frame mutation?
Changes in multiples of 3 bases, therefore no disturbance in actual reading frame
50
Types of effects of mutations on protein product
Silent
Mis-sense
Nonsense
51
What is a silent mutation?
No change in protein product
52
What is a mis-sense mutation
New mutant codon specifies a different aa with variable effects in final protein.
53
What happens in non-sense mutation?
```
New codon is either:
UUA
UGA
UAG
which signal stop to aa sequence, therefore nonfunctional protein
```
54
What are most translocations described as?
Reciprocal - one segment is exchanged for another segment among chromosomes
55
What is the Robertsonian translocation?
Non-reciprocal (unequal exchange) resulting in single fused chromosome from 2 acrocentric chromosomes.
56
Type of transmission of DiGeorge?
Autosomal dominant
57
Risk of schizophrenia if offspring has deletion for DiGeorge?
25%
58
Features of DiGeorge?
```
Mild-moderate LD
Facial deformities (cleft palate)
Absent/malformed parathyroids leading to hypocalcaemia
Broad nasal bridge
Articulatory speech and swallow problems
```
59
Location of transmission in Williams syndrome?
7q11 micro deletion
60
Features of Williams syndrome?
```
Hypercalcemia at birth
Supra valvular aortic stenosis
Moderate LD
Disinhibited disposition
Speech appears superficially fluent
Hyperacusis
```
61
Features of Angelman syndrome?
Low IQ
Jerky movements - especially hand flapping
Frequent smiling
Seizures
62
Features of Prader-Willi?
```
Obesity
Short stature
Small limbs
Decreased IQ
Hyperphagia and skin pricking
```
63
First law of Mendelian inheritance?
Law of uniformity;
| if two organisms that differ in one trait are crossed, resulting hybrid will be uniform in that trait
64
What is the second law of Mendelian inheritance?
Principle of segregation;
for any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent to the offspring, based on chance
65
What is the third law of Mendelian inheritance?
Principle of independent assortment;
66
How does X inactivation occur?
DNA methylation
67
What is unfavorable Lyonisation?
When during random X inactivation, most X chromosomes carrying normal alleles are inactivated
68
What type of inheritance is Tuberous sclerosis?
AD
| 1 in 30000
69
Features of Tuberous sclerosis
```
Adenona sebaceum
Normal to severe MR (heart)
Ash leaf macules
Brain hamartomas
Heart and kidney cysts
```
70
Features of Apert syndrome?
```
Variable MR
Cranio synostosis
Shallow orbits
Trapezoid mouth
Mitten hands and feet
AD
```
71
Inheritance of Noonan syndrome?
AD
| Chromosome 12
72
Risk of Noonan syndrome?
1 in 1500
73
Features of Noonan syndrome
```
Mild MR
Short stature
Nuchal oedema/webbed neck
Pulmonary stenosis
Cryptorchidism
```
74
Type of inheritance of Lesch-Nyhan syndrome
X linked recessive
75
Features of Lesch-Nyhan syndrome
Poor muscle control
Moderate mental retardation - year 1
Self-mutilating behaviour - lip and finger biting
Hyperuricaemia and Hyperuricosuria (gout and kidney problems)
76
Give e.g. of X-linked inheritance
Haemophilia A/B
Duchenne Muscular Dystrophy
Androgen insensitivity syndrome
77
Commonest cause of blindness in young men?
Commonest cause of blindness in young men?
78
Examples of Trinucleotide repeat disorders
Fragile X
Friedreich Ataxia
Huntingtons
Myotonic dystrophy
79
Where is the mutation in Fragile X?
CGG
80
Where is the mutation in Friedreich?
GAA
81
Where is the mutation in myotonic dystrophy?
CTG
82
Which two conditions result in most cases of mental retardation in males?
Downs
| Fragile X
83
Which gene results in Fragile X?
Expansion of CGG proximal to FMR1 gene
84
Features of Fragile X (male)
```
Enlarged testes
Prominent ear lobes
Protracting jaw
High pitched voice
Mental retardation
```
85
What are premutant carriers of Fragile X at risk of?
Developing intention tremor and ataxia after middle taxia
86
What are premutation carriers in Fragile X?
Those who carry increased number of CGG repeats in FMR1 locus but do not have clinical phenotype
87
What are women who are premutation carriers for Fragile X at risk of?
Premature ovarian failure
| Mild cognitive/behavioral abnormalities
88
Prevalence of Huntington's?
5 per 100000
89
What is the gene that causes Huntington's?
Expanded and unstable CAG trinucleotide repeat on short arm of chromosome 4-4p16.3
90
What is genomic imprinting?
Where the disease phenotype expressed depends on whether allele is maternally or paternally inherited.
91
What is polymorphism?
Variations in genetic make-up at a particular locus noted in the healthy population - at least in 1% of population
92
What are single nucleotide polymorphisms?
If polymorphism is to due to change in single nucleotide in a sequence.
93
How can single based polymorphisms be assayed?
DNA sequencing
| DNA chips
94
What are variable number of tandem repeats?
Polymorphism due to varying number of repeats in specific region of chromosome.
95
How are variable number of tandem repeats classified?
Short tandem repeat polymorphism
Microsatellite (2-6 bases)
Minisatellite (20-bases)
96
Where do most polymorphisms occur in a gene?
Introns
97
Features of those with short allele of 5HTTLPR?
Low expression of serotonin transporter
98
What is short variant of 5HTTLPR speculated to be linked to?
Higher incidence of affective disorders, neuroticism, anxiety and PTSD
99
When is southern blotting used?
For detecting specific sequence of DNA
100
When is western blotting used?
Detection of specific protein after electrophoresis
101
When is northern blotting used?
Detection method for specific RNA after electrophoresis.
102
What does PCR do?
Amplifies minute amounts of DNA, allowing further analysis
103
What does the Hardy Weinberg equilibrium determine?
The frequency of an abnormal gene or genotype in the population.
104
What is epistasis?
Gene-gene interaction, particularly between different alleles
105
What is locus heterogeneity?
When same disease phenotype can be caused by mutations in different loci.
106
What is allelic heterogeneity?
Same disease phenotype resulting form different types of mutations at same loci.
107
What is pleiotropy
When single disease-causing mutation affects multiple organ systems.
