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Genetics Flashcards

1
Q

Streak ovaries in turners syndrome. Means what histology app

A

Ovaries are composed of only connective tissue

There are no developing follicles

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2
Q

What is cause of follicle less streak ovaries in turners syndrome

A

Loss of paternal chr X
Loss of all ovarian follicles by age 2
Ovaries develop normally in fetal life but by 2 they loose their follicles
Turner girls are infertile have amenorrhoea
No menses or breast
Only pubic hair are present

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3
Q

Most common cardiac abnormality with turners

A

Bicuspid aortic valve

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4
Q

Therapeutic radiation used in cancer treatment causes what effects

A
  • free radical damage— cell as well as DNA damage
    — DOUBLE stranded DNA BREAKS
    SINGLE STRAND BREAKS ARE NOT EFFECTIVE BECAUSE THEY ARE EASILY REPAIRED BY POLYMERASE
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5
Q

Which nucleosides undergo dna methylation

A

Only cytoside and adenine

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6
Q

Point mutation in beta globin gene
With change of glutamic acid to valine at 6th position

What dz

A

Sickle cell disease

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7
Q

Examples of missense mutation

A 
Sickle cell glu A - valine
Others
Glutamine-valine
Histidine - leucine
Valine-glutamic acid
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8
Q

Name trinucleotide expansion genetic disease

A

Huntington
Freidrichs ataxia
Fragile X
myotonic dystrophy

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9
Q

Genomic lmprinting is selective inactivation of genes of either maternal or paternal origin
15q same region deletion gives two syndrome they are

A

Prader willi—when chr with deletion comes from papa

Angelman— mommy gene has deletion

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10
Q

What is pleio tropy

A

One gene mutation leads to multiple unrelated abnormalities

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11
Q

Linkage disequillibrium occurs due to

A

Physical proximity of genes on the same chromosome

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12
Q

If two genetic loci are on different strands then their gametes will have each halplotype with equal 1:4 frequency

This is called

A

Linkage equillibrium

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13
Q

What does hla DQA1 and HLA DQ B1 code for

A

A1 alpha chains on mhc 2

B1 beta chains in mhc 2

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14
Q

Severity of mitochondrial disease is related to proportion of abnormal to normal mitochondria
What is heteroplasmy

A

Presence of different mitochondrial genomes mutated as well as wild in single cell

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15
Q

Law of segregation is seen in

A

Gametogenesis
Ie separation of paired chromosomes
So that offspring inherit only half of each parents composition

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16
Q

Congential hypothyroidsm babies are normal at birth

Symptoms come at around 2 months becausd

A

Maternal T4 in circulation helps

It wanes by 2 months

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17
Q

Symptms of congenital hypothyroidism

A 
Lethargy
Enlarged fontanelle
Protruding tongue
Poor feeding
Constipation
Dry skin
Jaundice

Increased TSH
LOW FREE T4

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18
Q

Affected males will always produce unaffected sons and carrier daughters

Carrier females have 50percent chance of producing affected son or carrier daughter
This inheritance is

A

XL recessive

Male offspring of unaffected parents is affected

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19
Q

Affected person has at least one parent who is also affected regardless of sex

He will always produce affected daughters but none of the sons will be affected

A

X linked dominant

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20
Q

In FISH test
Gold standard for genetic

genes of interest are hybridised with fluroscently labelled DNA probe

Lack of fluroscent signal suggests

A

Microdeletion

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21
Q

Autosomal recessive microtubular defects dynein arm is

A

Kartagener syndrome

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22
Q

Primary site of ribosomal RNA rRNA TRANSCRIPTIOM

A

Nucleolus

Contains RNA polymerase 1

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23
Q

Function of RNA POLYMERASE 1

A

Strictly seen only in nucleolus
Only one function to transcribe 45s Pre-rRNA gene to single template

It gets further processed to 18s, 5.8s and 28s rRNA

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24
Q

Two places where endonuclease enz plays a role

A

DNA REPAIR

RNA SPLICING

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25
Q

Role of RNA POLYMERASE 2

A

Transcription ie mRna synthesis

Also forms small nuclear RNA and microRNA

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26
Q

Function of RNA POLYMERASE 3

A

Synthesis of tRNA and 5S rna

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27
Q

Of all rRNA

5s rna genes are located

A

Outside nucleolus

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28
Q

Post transcriptional RNA SPLICING
Is done by SN RNA
HOW

A

It removes introns from hnRNA

Which contains GU at 5’ splice site and AG at 3’ splice site

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29
Q

In eukaryotes things required for translation initiation are

A 
Both ribosomal units- 60s and 40s
Associated rRNA and mRNA
INITIATION FACtors
Initiator tRNA charged WITH METHIONINE 
And GTP
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30
Q

Two promoters situated upstream the transcription initiation site in dna are

A

Tata box—25 bp upstream

And
Caat box - 70 to 80 bp upstream

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31
Q

Which human enz is a reverse transciptase

A

Telomerase

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32
Q

Component of telomerase are

A

TERC—telomerase rna component
TERT- rev transcriptase enz

Funxtion of terc—built in RNA TEMPLATE WHICH IS CONSTANTLY READ BY REVERSE TRANSCRIPTASE ENZ TO PRODUCE ssDNA

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33
Q

What is the function of telomerase

A

To keep the telomeres long
Since after critical shortening programmed cell death occurs

Cancer cell and adult stem cells have long telomeres dont die

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34
Q

What is added to 3’ end of chromosome by telomerase

A

Telomeres are lengthened by enz telomerase

It adds TTAGGG at 3’end of chromosomes

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35
Q

Stem cells on skin are located in

A

Epidermal basal layer

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36
Q

What is kozak sequence

A

It is a sequence for initiation of translation on mRNA in eukaryotes

it is gcc-Rcc-AUG
Here R has to be adenine or guanine 3bases upwards from AUG to have translation started

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37
Q

Who recognises AUG start codon in protein translation

A

40s smaller ribosomal subunit
Binds to 5’ cap of mRNA and scans for AUG CODON
If it finds AUG. with kozak consensus sequenxe upstream it translation is started

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38
Q

What is prokaryotic equivalent of kozak consensus sequence

A

Shine dolgarno sequence upstream for AUG codon

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39
Q

What is co translation protein targeting

A

Process wherein SIGNAL RECOGNITION PARTICLe

recognise the n terminal amino acid sequence
Of the enlarging polypeptide and tagg it

It helps to transport it to rough ER

40
Q

What is the component and function of larger ribosomal subunit

A

Large ribosomal subunit has enz peptidyl transferase

Which catalyses the peptide bond formation

41
Q

What is translocation in protein synthesis

A

During elongation the ribosome moves 3 nucleotides towards 3’ end of mRNA
Advancing peptidyl tRNA moves from A TO P site

Needs GTP hydrolysis
Needs elongation factor 2

42
Q

Genetics of sickle cell disease

A

A to T Mutation in beta globin gene

Resulting in glutamic acid to be replaced by valine at 6th position

43
Q

Small gap in the tip of long arm of chromosome X

Leads to which disease

A

Fragile X syndrome
Most common inherited cause of intellectual disability

Due to CGG trinucleotide expansion

44
Q

Why is fragile X CALLED SO

A

When pts cells are cultured in folate deficient medium

The area of increased repeats do not stain and appears broken

Hence a gap near tip of long arm of chromosome X

45
Q

What is the genetic abnormality in fragile X

A

CGG trinucleotide expansion repeats in
FxMR1 gene aka fragile x mental retardation gene 1

It is located on long arm of chromosome X

46
Q

Features of fragile X syndrome

A

Intellectual problems with delayed motor and language milestones
Everything is big— macrocepahly big forehead jaw, chin and ears
Big testes -macroorchidism
Long narrow face

Features are subtle in infancy but they become prominent in puberty

47
Q 
What do these features point to
Lens dislocation
Aortic root dilation
Arachynodactyly
Scoliosis
Mitral valve prolapse
Breast bone changes 
Tall pts thin slender
Flat feet
Increased arm to height ratio
A

Marfans

48
Q

Most common genetic cause of intellectual disability

Most common inheritable cause of intellectual disability

A

Genetic— downs

Inheritable— fragile X

49
Q 
What does these features point to
Long legs
Intellectual disability
Sparse facial and body hair
Infertility
Gynaecomastia
Cryptorchidism
A

Kleinfelters syndrome

Testes is fibrotic and cryptorchid
No testosterone
Causes oligospermia and hence infertility

50
Q

In general most enz deficiency have what type of genetic inheritance

A

Autosomal recessive

51
Q

In exam confusion can arise between primary ciliary dyskinesia and cystic fibrosis

What is the pathogenic difference

A

Kartagener is abnormal ciliary motion due to DYNEIN arm defect

Cystic fibrosis is due to CFTR gene mutation and impaired chloride ion transport

52
Q

In exam confusion can arise between primary ciliary dyskinesia and cystic fibrosis

What is the diagnostic ways to differentiate

A

Kartageners needs LOW NO levels in nasal specimens
Bronchoscopy and microscopy shows impaired cilia motility

Cystic fibrosis— has elevated sweat chloride levels and abnormal nasal transepithelial potential difference

Then obviously genetic testing helps

53
Q

In exam confusion can arise between primary ciliary dyskinesia and cystic fibrosis

Extapulmonary manifestation differ which are

A

Kartagener has— normal growth situs inversus, and infertility due to immotile sperms

Cystic fibrosis pts — failure to thrive, pancreatic insufficiency and infertility due to bilateral absence of vas deferens( azospermia)

54
Q

Inherited disorder and associated cvs developmental defects

Downs syndrome

A

Endocardial cushion defects

That is osteum primum asd and regurgitants AV valves

55
Q

Inherited disorder and associated cvs developmental defect

Digeorge synd

A

Tof
Interrupted aortic arch
Remember 3rd ph pouch problem

56
Q

Inherited disorder and associated cvs developmental defect

Freidrichs ataxia

A

Hypertrophic cardiomyopathy

57
Q

Inherited disorder and associated cvs developmental defect

Marfans

A

Aortic root dilatation dissection and aneurysm due to cystic medial necrosis

Mitral valve prolapse

58
Q

Inherited disorder and associated cvs developmental defect

Tuberous sclerosis

A

Cardiac rhabdomyomas

Causing valvular obstruction

59
Q

Inherited disorder and associated cvs developmental defect

Turners syndrome

A

Coarctation of aorta

Biscuspid aortic valve

60
Q

What do these features point to

Skin normal in infancy
By 1 year sun exposed areas shows signs of sunburns
Atrophic scaly skin
Light snd dark pigmented skin with telangiectasia
Skin malignancies like malignant melanoma, SCC, BCC as early as 5 to 6 years to age

A

Xeroderma pigmentosa

Autosomal recessive
Defective nucleotide excision repair of DNA damaged by UV LIGHT

61
Q

Steps in nucleotide excision repair are

A

Uv exposure causes thymine dimers
Deformed dna strand identified by ENDONUCLEASE COMPLEX
ss breaks in DNA made up and downstream the dimers
Removed
Dna polymerase replaces the lost segment of dna
Dna ligase seals it

62
Q

Most common inherited cause of aplastic anemia

A

Fanconis anemia

63
Q

Genetics of fanconis anemia

A

AR

MUTATION IN GENE RESPONSIBLE FOR REPAIR OF INTERSTRAND DNA CROSS LINKS

64
Q

What does this features point to

Short stature
Absent thumbs
Increased malignancy
Aplastic anemia reduced rbc and other lines

A

Fanconis anemia

65
Q

Name imp mitochondrial inheritable dis

A

Lebers hereditory optic neuropathy

myoclonic epilepsy with ragged red fibres

Melas/ mitochondrial encephalopathy with lactic acidosis and stroke like episodes

66
Q

What helps transcription in eukaryotic genes

A

Promotor where rna polymerase and transcription factors binds

Enhancer— which enhances / acclerates the rate of transcription

Promoters are caat box and tata box upsteam to start codon ATG

67
Q

What do enhancer sequences bind to

A

Activator protein
This complex act to help bending of DNA
Which allows activator proteins to interact with transcription factors and RNA polymerase 2 to increase the rate of transciption

68
Q

Location of promotor and enhancer

A

Promotor is upstream towards 5’ end of start codon

Enhancers can be anywhere— up down in introns etc

69
Q

Role of silencers

A

Bind to repressor proteins

Reduce the rate of transcription

70
Q

Name the phases of arrests in gametogenesis

A

Oogonia—G0
Primary oocyte— prophase M1
Secondary oocyte-metaphase M2
Mature ovum—telophase M2

71
Q

Arrested primary oocyte resumes meiosis 1 under the effect of

A

FSH AND LH

72
Q

Prior to fertilization

Secondary oocyte released from ovum is arrested in

A

Metaphase of M2

73
Q 
What do these features point to
Clenched fist with overlapping fingers
Low set ears
Micrognathia—small jaw mandible
Prominent occiput
Heart and renal defects
Limited hip abduction
Rockerbottom feet
A

Edwards syndrome
Trisomy 18

Majority die by 2
If not severe intellectual disability

74
Q

What do these features point to

Low set ears hypertelorism
Broad nasal bridge
Microcephaly
Developmental delay
Failure to thrive
Hypotonia
Weak cat like cry
A

Cri du chat syndrome

5p deletion

75
Q

What are the components of telomeres

Function

A

Telomere are complex of protein( shelterin) and DNA REPEATS TTAGGG which is added by enz telomerase

This telomeres prevent chromosomal degradation
Prevent fusion with neighbouring chromosomes

76
Q

Most common sex chromosomal abnormality in females

A

47 XXX
Incidentally detected
Patients are normal

77
Q

What happens when one ovum is fertilised by 2sperms

A

Karyotype becomes 69 XXX or 69 XXY

they are partial molar pregnancy
Ovum has maternal chromosomes so fetal parts do develop unlike in complete mole

78
Q

What happens when ovum without maternal chromosomes fertilise

A 
Complete molar pregnancy
The sperm ( with 23X haplotype) contributes chromosomes solely
Which duplicate into 46 XX of only paternal DNA

46YY ( with 23 Y) IS NOT compatible and not seen in zygotes
46XY molar is also possible but rare wherein two sperms with x and y haplotypes fertilize empty ovum

79
Q

Why do turner girls have short height

A

Loss of entire or part of X chromosome leads to loss of SHOX gene

It normally promotes long bone growth

80
Q

Name the mutation in which difference in number of niucleotides is not divisible by 3

A

Frame shift mutation

Due to insertion or deletion of nucleotides

81
Q

What tests determines type and quantity of RNA based in size

A

RNA— norther blot tests

82
Q

Hla genes are located on

A

Single chromosome 6
HLA A B C are on short arm ch6
DQ DR DP are on long arm chr 6

83
Q

Since all hla genes are on the same chromosome
Their cross over is negligent
This helps what

A

Hla inheritance follows rules of haplotype
Ie two siblings have 25 percent chance of being identical and being non identical
And 50 percent chance of being half identical

84
Q

TTN. Gene mutation

Usually a non sense mutation leads to

A

Truncated titin protein

Dilated cardiomyopathy

85
Q

Which genetic disease leads to right ventricular myocardium scarring
Ventricular arrhythmias
Sudden cardiac death

A

Arrythmogenic right ventricular cadiomyopathy

Caused by impaired desmosomes
Because of mutations in genes for proteins of desmosomes like desmoplakin and plakoglobin

86
Q

Mutations in NOTCH 1 gene

A

It codes for transcription regulatory proteins
Mutations in NOTCH1 gene
Leads to familial bicuspid aortic valve

87
Q

Examples of point mutation are

A

Mis sense mutation- can be convervative( properties remain same) non conservative( properties change)

Non sense- early stop codon

Silent — no change in amino acid coded

88
Q

If a karyotype shows shortened chromosome 22 and elongated chromosome 9
What disease is seen

A

Chronic myeloid leukemia
It is philadelphia chromosome
Trans 9-22 bcl-abr fusion

89
Q

Genetic causes / phenomenons in downs syndrome

A

In order of occurence

  1. Meiotic non disjunction
  2. Unbalanced robertsonian translocation
  3. Mosaicism in less than 2% affected pts due to non disjunction during mitosis
90
Q

Assay to detect proteins in a mixed sample

A

Western blot

91
Q

Steps of western blot

A

Separation of proteins on gel electrophoresis
Primary antibody added
Secondary labelled antibody added to detect the complex of protein and primary antibody

92
Q

Malignancies increased in downs

A

ALL

ACUTE MEGAKARYOCYTIC LEUKEMIA

93
Q

Function of cyclin D

A

Helps in G1 —-> S transition

94
Q

Cyclin D is produced in which phase of cell cycle

A

G1

Hence helps in G1S TRANSITION

95
Q

Overexpression of cyclin D results in

A

Unchecked g1/S transition
Hence uncontrolled proliferation
Malignancy

96
Q

Git diseases in downs

A 
Tracheo esophageal fistula
Duodenal atresia
Celiac disease
Hirschsprung disease
Imperforate anus

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