Genetics Mini 1

Front 1

What is heridatary material?

Back 1

Chromosomes

Front 2

What shape do chromosomes have?

Back 2

Rod shaped thread like structures

Front 3

What are chromosomes made up of?

Back 3

Made up of DNA, Histones & other proteins (together
constitute Chromatin)

Front 4

How many chromosomes are there? How many pairs?

Back 4

46 chrom= 23 pairs

Front 5

What is chromatin m/u of?

Back 5

omatin m/u of mainly DNA but also histones(+chg) they also regulate flow of genetic information. Genetic info is req for synthesise in blood

Front 6

What are constiture genes?

Back 6

Are expressed at certain times (like a job work only 8-5)

Front 7

What are inducable genes?

Back 7

Are expressed when there is a need

Front 8

Chromosomes exhibit a definite pattern of...

Back 8

Chromosomes exhibit a definite pattern of
Morphology and number in individual organism

Front 9

In a karyotype what phase is suspended & what is displayed?

Back 9

The number, size and shapes of Metaphase
Chromosomes constitute- KARYOTYPE-cytogenetics

Front 10

How many chromatids are made in metaphase? what holds them together?

Back 10

Each metaphase chromosome is made up of
two chromatids. Held together by an area of
primary constriction called centromere.

Front 11

What color stain does centromere reveal?

Back 11

Centromere is a pale staining region.

Front 12

Centromere connects what? What is it rich in? What is a kinetochore?

Back 12

Centromere, which connects two sister chromatids in dividing cells, is an A – T rich region. It binds several proteins with high affinity. The complex of A-T rich region of DNA and proteins in centromere is called as Kinetochore.

Front 13

Why is kinetochore important?

Back 13

Kinetochore is an essential structure for chromosomal segregation during cell division.

Front 14

What is a telomere? What is telomerase rich in?

Back 14

The structural region at the ends of each chromosome. Made of TG rich repeat sequences(eg.5’-TTTGGG- 3’). Telomerase protein is important in maintaining telomere.

Front 15

What is the purpose of histones?

Back 15

Histones regulate flow/expression of genetic information

Front 16

What letter signifies short arm & long arm?

Back 16

Short=p
Long arm=q

Front 17

Which chromosomes signify sex?

Back 17

Chromosome pair 23

Front 18

What cells are diploid cells? How many sets of chromosomes do they contain.

Back 18

All somatic cells are diploid cells. They contain two sets of chromosomes. Gametes(sperm & ovum) are haploid cells.

Front 19

What are an example of haploid cell? How many chromosome sets do they have?

Back 19

Gametes(sperm & ovum) are haploid cells. They have one set of chromosomes (half the number of diploid cells) .

Front 20

What determines position of centromere? What are the types?

Back 20

Based on the position of centromere, the chromosomes are classified into:

1. Metacentric – in the middle
2. Sub metacentric – on either side of the mid point
3. Acrocentric – Near the end
4. Telocentric - At the extreme tip.

Front 21

What are autosomes?

Back 21

Majority of the chromosomes present in the nucleus are autosomes. In humans there are 22 pairs (44) of autosomes in diploid cells & 22 in haploid cells.

Front 22

What are sex chromosomes also called? What is homogametic & heterogametic?

Back 22

They are also called
as allosomes. In humans there is a single
pair of sex chromosomes. In females both the sex chromosomes are alike (XX). This phenomenon is called as homogametic. On the other hand in males the two sex chromosomes are not identical (XY). This pattern is heterogametic .

Front 23

What are the numerical changes in chromosomes?

Back 23

Based on number of sets;
i) Haploid: Single set
ii) Dipliod: Two sets
iii) Polypliod: More than two sets.

Front 24

What is the Approximate number of protein coding genes present in haploid human genome?

Back 24

Approximate number of protein coding genes present in haploid human genome: 25000

Front 25

How is proteins coded?

Back 25

mRNA

Front 26

What is alternatice splicing?

Back 26

Alternative splicing of precursor mRNA is mainly responsible for the formation of multiple proteins from a single gene

Front 27

What is the central dogma?

Back 27

DNA--Tc--RNA--Tl---Protein

Front 28

What is transcription?

Back 28

It is the process by which RNA is synthesized from DNA

Front 29

What occurs in ea. Tc process?

Back 29

i) Only a portion of DNA takes part and that portion may be called as gene
ii) Of the 2 strands of DNA(gene) only one strand takes part in the synthesis of new RNA. It is called as template strand. The opposite strand is called as coding strand

Front 30

What enzyme is important in Tc? What is promoter seq.? What directin is new RNA synthesized?

Back 30

RNA polymerase is the enzyme responsible for the process of transcription

Each gene contains a promoter sequence meant for initiation

The new RNA strand is synthesized in 5’ to 3’ direction

Front 31

What is the newly synthesized RNA strand called? What is it complementary to?

Back 31

The newly synthesized RNA strand is called as primary RNA transcript

The primary RNA transcript is complimentary to the template strand of the DNA (gene), except U (uracil) is present in place of T (thymine) and ribose is the sugar in place of deoxyribose

Front 32

5 ---A-C-T-G-C-G-T-A-A-A-G-T-C-A-G-T----3
3 ---T-G-A-C-G-C-A-T-T- T-C-A-G-T-C-A----5

Back 32

5---A-C-U-G-C-G-U-A-A-A-G-U-C-A-G-U---3

Front 33

What are the Post Transcriptional Modifications of precursor mRNA to form functional mRNA ?*** very important

Back 33

Important events are;
i) Addition of 7 methyl Guanine cap at 5’ end
ii) Addition of poly A tail at 3’end
iii) Splicing- ie. Removal of non coding intron regions and joining of coding exon regions. This is accomplished by spliceosome complex made up of small nuclear ribonucleoprotein

Front 34

A gene coding for the proteins of potassium channel is transcribed to form pre.mRNA with __ exons, __of them are subjected to alternative splicing thereby capable of giving rise to over 500 different proteins

Back 34

A gene coding for the proteins of potassium channel is transcribed to form pre.mRNA with 35 exons, 8 of them are subjected to alternative splicing thereby capable of giving rise to over 500 different proteins

Front 35

What percentage of diseases is affected by alternative splicing? Ex?

Back 35

15% of genetic diseases are due to mutation in splice sites. Best example is Beta thalassemia

Front 36

What do the introns start with and end with?

Back 36

Normally all the introns start with GU (5’ ) and end with AG (3’)

Front 37

How many codons can be created how many bases? How many amino acids?

Back 37

Considering 4 bases in mRNA 64 codons can be created. Among them 61 code for 20 different amino acids. Remaining 3 are called as stop codons or non sense codons

Front 38

What is translation? Where does it take place?

Back 38

It is the process by which the genetic information present in mRNA as codons are translated to form amino acid sequence of protein
Translation takes place in ribosomes of the cell

Front 39

What occurs during translation?

Back 39

During translation;
i) mRNA serves the genetic information for the formation of amino acid sequence of protein

ii) tRNA acts as career of amino acids to the site of protein synthesis

iii) rRNA serves as the integral part of ribosomes, and thereby coordinating the process of translation

Front 40

What does translation process involve?

Back 40

Activation of amino acids to form amino acyl tRNA

Front 41

What are the types of post translational modificatins?

Back 41

Cleavage , glycosylation , phosphorylation, hydrxylation, incorporation of prosthetic groups, metals etc

Front 42

Where can the expression of genetic information could also be controlled at the level of

Back 42

i) Post transcriptional processing of precursor mRNA
ii) Translation

Front 43

What are pseudogenes? How many types, what?

Back 43

Pseudogenes are non functional genes present widespread througout the genome

Their nucleotide sequences resemble that of known genes and gene families

They are of 2 types;
Non processed
Processed

Front 44

What are non processed psuedogenes?

Back 44

They are dead genes, but functional once upon a time, and formed as byproducts during evolution

Front 45

What are processed pseudogenes?

Back 45

They are integrated into the human genome as a result of the process called as Retrotransposition

These genes are created from mRNA as a result of reverse transcription and get inserted into the human genome

In Olfactory receptor (OR) gene family there are over 600 pseudogenes

Front 46

What is a gene?

Back 46

Fundamental unit of genetic expression for a feature (Character).

Front 47

What is a locus?

Back 47

Specific location (site) in chromosome
for a gene.

Front 48

What is an allele?

Back 48

Alternative forms of genes for
specific character, present at the same locus in homologous chromosome.
They are units that determine the heritable characters.

Front 49

What chromosome is responsible for eye color?

Back 49

Chromosome 15

Front 50

What is homozygous?

Back 50

If the two alleles, for a particular character, are identical

Front 51

What is heterozygous?

Back 51

If the two alleles, for a particular character, are not identical

Front 52

What is dominant?

Back 52

In heterozygous condition, the allele which is responsible for the expression of a character

Denoted by Capital letter

Front 53

What is recessive?

Back 53

The allele, which does not express its character in heterozygous condition

Denoted by small letter

Front 54

What is autosomal?

Back 54

Refers to the expression of allele (gene) in autosomes. Autosomal inheritance is the inheritance of characters through the alleles present in autosomes.

Front 55

What is X-Linked?

Back 55

Refers to the expression or inheritance of characters through X chromosomes.

Front 56

What is phenotype?

Back 56

Outward appearance & Physical
characteristics
Examples:
Brown eye color
Curly hair
Hb A
Hb S

Front 57

What is genotype?

Back 57

Genetic set up (pattern of alleles) in
either autosomes or sex chromosomes for
a particular character.
Example :
Brown eye color
BB = Brown (homozygous dominant)
Blue eye color
bb = Blue (homozygous recessive)
Brown eye color
Bb = Brown (heterozygous)

Front 58

What is Single Gene inheritance? What law does it follow?

Back 58

In general Single gene inheritance represents the
Inheritance pattern of a pair of genes(alleles) present in
a pair of Homologous chromosomes from parents to
offspring

follows Mendel’s
First Law (Law of Segregation)

Front 59

The basic aspects of the Mendelian principle for single gene inheritance are:

Back 59

Existence of two genes (Alleles) for a single character (trait)

The two alleles may be identical (homozygous) or different (heterozygous).

If heterozygous, the dominant allele is responsible for phenotypic expression

Front 60

Single Gene inheritance:
EExee (E=free, e=attached)
Genotype gametes?
Genotype & Phenotype of Offspring?

Back 60

EE X ee
(Homozygous Free)(Homozygous attached)

Genotype of gametes: E & e

Genotype and Phenotype of Offspring:
Ee (Heterozygous Free)

Front 61

EexEe

Geno & Pheno of parents?
Geno of gametes?
G & O of offspring?

Back 61

G&P Parents:
Ee (Hetero Free) x Ee (Hetero free)

Geno of gametes: E or e & E or e

G&P of offspring:
EE (homo free), Ee (hetero free), ee (homo attach)

Front 62

EexEe

What is the geno & pheno ratio? What are the possible pheno & geno?

Back 62

1:2:1 genotype
3:1 phenotype

1/4 = EE – Free ear lobe
1/2 = Ee - Free ear lobe
1/4 = ee - Attached ear lobe

Front 63

What are the examples of non mendalian Inheritance patterns?

Back 63

Incomplete Dominance
Codominance

Front 64

What is Incomplete Dominance?

Back 64

Inheritance of hair pattern; curly or straight

Front 65

What would be the pheno & geno of the gametes if the parent genotypes were CC(curly) x cc(straight)

Back 65

Cc heterozygous wavy hair

Front 66

What are the gametes of CcxCc?

Back 66

CC; Cc; Cc; cc

Genotype: Cc, Cc, cc 1:2:1
Phenotype: Curly, Wavy, Straight 1:2:1

Front 67

What is codominance?

Back 67

Both alleles participate in phenotype expression

Ex. ABO blood group system

Front 68

What is ABO blood group system also an example of? How is it determined?

Back 68

Multiple Allele pattern

ABO blood groups are genetically determined by a locus on Chromosome 9

Front 69

The three alleles ABO determine how many phenotypes? Which are dominant?

Back 69

4 phenotypes

Dominant: A & B
Recessive: O

Front 70

What are the possible gametes if the parent is IbIb x Iai

Back 70

IaIb = 1/2
Ibi= 1/2

Front 71

What are the possible gametes if the parent is IaIb x ii

Back 71

Iai = 1/2
Ibi = 1/2

Front 72

What is Proband/ Propositus/ Index case?

Back 72

Refers to the member of the affected family, who first reports the case to Genetic consultant or Clinician.

Front 73

What are the relatives based on degree:

Back 73

First Degree: Parents, sibs and offspring of the proband

Second Degree: Grandparents, Uncles,
Aunts, Grandchildren, Nephews and Nieces.

Third Degree: Example; First cousins.

Front 74

What is consanguity, isolate, sporadic?

Back 74

Consanguinity/Consanguineous: Couples having one or more ancestors in common

Isolated: If there is only one affected member in a family.

Sporadic: If the disorder is due to new mutation in proband.

Front 75

What are the classifications of genetic disorder?

Back 75

Single Gene Disorders

Chromosomal Disorders

Multifactorial Disorders

Front 76

What is single gene disorder? How is it caused? What are the types?

Back 76

Single gene disorders in general follow Mendelian inheritance pattern.

Caused by mutation of one or both the genes in a pair.

There are four different types:

Autosomal Dominant
Autosomal Recessive
X – Linked Dominant
X – Linked Recessive

Front 77

Where is new mutation more evident? How is it likely called?

Back 77

Autosomal dominant diseases

Most likely a gene transmitted by one of the parents undergoes mutation.

Front 78

What disease is an example of new mutation? Why?

Back 78

Achondroplasia b/c disease limits the potential for reproduction

Front 79

What is germline mosaicism? What are the details? How could it be caused?

Back 79

Mosaicism is the presence of more than one genetically distinct cell line in the body.

Apart from new mutation, occasionally individuals may exhibit autosomal dominant or X-linked diseases with no previous family history. This could be due to Germline mosaicism.

Could be caused by mutation in germ line cell w/o affecting somatic cells.

Can persist in all clonal descendants

Front 80

What disorder is usually found in germline mosaicism? What type of disorder is it?

Back 80

Osteogenesis imperfecta, where mutation in type I collagen gene leads to the formation of abnormal collagen --- brittle bones and frequent fractures.
also in Duchenne Muscular Dys, Hemophilia A, rarely Achondroplasia

Autosomal dominant disorder

Front 81

What is reduced penetrance? What disease is it found and what type of dominance?

Back 81

It is the pattern where abnormal phenotypic expression is not observed at all.
Retinoblastoma, a malignant eye tumor (Autosomal dominant) is a good example for reduced penetrance. Here 10% of the obligatory carriers do not have phenotypic expression. So the penetrance is 90% .

Front 82

What is Age dependent penetrance? What disease is common?

Back 82

A delay in the age of onset of a genetic disease is called as Age-Dependent Penetrance.

Hutington

Front 83

What is variable expression?

Back 83

Severity of the phenotypic expression, sometimes the penetrance may be complete but the severity varies. even if ppl have the same genotype.

Front 84

What is penetrance? How is it different from variable expression?

Back 84

Penetrance is all or none phenomenon.

Variable expression refers to severity of phenotypic expression

Front 85

What is pleiotropy? ex?

Back 85

When a single abnormal gene or gene pair produces diverse phenotypic effects, involving different organ systems and clinical symptoms, its expression is said to be pleiotropic. ie. the genes have more than one discernible effect on the body.

Marfaran syndrome, autosomal dominant

Front 86

What is heterogeneity?

Back 86

This is in contrast to Pleiotropy. Here similar types of phenotypic expression (abnormal manifestations) are exhibited different mutation

Front 87

What is allelic heterogeneity? ex?

Back 87

Different types of mutation in alleles located in same locus–
eg. Cystic Fibrosis

Caused by different types of mutation in CFTR gene

Front 88

What is locus heterogeniety? ex?

Back 88

Mutation of alleles present at different loci, may be at different chromosomes
eg. Retinitis Pigmentosa –visual impairment, could be autosomal dominant, autosomal recessive or X-linked

Front 89

If a trait generally appears in every generation what inheritance is it?

Back 89

auto dominant

Front 90

Each pregnancy is an "independent event" so even after an affected child, the chance to produce another affected child in the subsequent pregnancy is?

Back 90

remains 50%

It is possible that no child would be affected or every
child is affected

Front 91

Incidence of certain AD diseases is higher at specific geographic locations are?

Back 91

1:500 - Familial Hypercholesterolemia (FH) in European and Japanese populations

1: 1000 - Myotonic Dystrophy certain parts of North America

1:2500 to 1:3000 for Huntington Disease, Neurofibromatosis (NF1) in North Europe.

Front 92

If both parents are affected Aa x Aa what are the gametes?

Back 92

AA, Aa, aa==1:2:1
3 affected:1 normal

Front 93

One normal parent & one affected parent what are the pheno & geno?

Back 93

aa x Aa
Aa, Aa, aa, aa
2 affected: 2 normal

Front 94

What are examples for autosomal dominant gene disorders?

Back 94

Neurofibromatosis
Achondroplasia
Marfan Syndrome
Huntington disease
Myotonic dystrophy

Front 95

What is the incidence of Neurofibromatosis (Type 1)? How many are due to new mutation?

Back 95

Incidence: 1:3000 to 1:5000.

50% of cases due to new mutation

Front 96

Where is the mutation found for Neurofibromatosis Type 1?

What type of inheritance is it?

Back 96

High mutation rate mainly due to large gene (400kb in long arm of chromosome 17).

Pleiotropy

Front 97

What does NF1 gene cause, and what is it also an example of?

Back 97

defective production of Neurofibromin

Allelic heterogeneity

Front 98

Where is the mutation of achondroplasia? What is the incidence, penetrance? What type of dominance?

Back 98

Mutation in chromosome 4p

Incidence: - 1:1500

Complete Penetrance

80% to 85% of patients are new mutants

Homozygote much more severe (mostly infantile deaths)

Heterozygotes - normal intelligence and normal life

Also considered as an example for incomplete dominance

Front 99

What is a common characteristic of achondroplasia? What are the features?

Back 99

Skeletal disorder
short limbed dwarfism

Features:
Long, narrow trunk
Short extremities, particularly proximally
Large head , low nasal bridge, narrow foramen magnum
Exaggerated lumbar lordosis (forward curvature of spine)

Front 100

What is familial testotoxicosis? What type of dominance?

Back 100

Male limited precocious puberty

Autosomal dominant

Features: Boys develop secondary sexual characters as early as at about 4yrs.
Can be transmitted to male child either by Unaffected mother of affected father

Front 101

Where are the manifestations seen in Autosomal Recessive disorders? Who acts as a carrier?

Back 101

seen only in Homozygotes

Carriers: Heterozygotes

Front 102

Both males and females are affected by AR disorders what is the exception?

Back 102

Hereditary hemochromatosis

Front 103

What is a feature of AR disorder regarding mutant alleles?

Back 103

Mutant alleles may remain in heterozygous state (without phenotypic expression) in a family for numerous generation

Front 104

Which AR dieases is common among population that consanguinity would not play a role?

Back 104

Cystic Fibrosis

Front 105

What is coefficient of inbreeding (F)? What is it based on?

Back 105

Coefficient of inbreeding (F) is the probability that a homozygote has received both alleles at a locus from same ancestral source

Based on Consanguinity

Front 106

What is Tay Sachs disease? What is it an example of? What type of disorder is it? Who is it common? What enzyme is deficient? What accumulates?

Back 106

Lysosomal Storage Disorder

Example for a Sphingolipidoses

Example for ethnic variation in allele frequency

Common among Ashkenazi Jews of N. America

Deficiency of the enzyme Hexosaminidase A

Accumulation of ganglioside, GM2

Front 107

Where is the mutation found for Tay Sachs?

Back 107

Mutation of HEXA gene

Chromosome 15

Front 108

Where is the mutation found in Sickle Cell Anemia?

Back 108

Mutation of gene coding for B chain of Hb

Chromosome 11

Front 109

What is a condition concurrent?

Back 109

A condition concurrent is two conditions that are capable of occurring together, and the parties are bound to perform at the same time.

Ex: I will sell you a book for $10. (you giving me the book and me giving you the $10 are concurrent)

Front 110

What is Xeroderma Pigmentosum? How is it caused? What are the symptoms?

Back 110

A rare genetic disorder of DNA Repair (Nucleotide excision repair)

Caused by gene mutation – leading to defective formation of protein/enzyme required for nucleotide excision repair of pyrimidine-pyrimidine dimer

Symptoms: UV light sensitivity Skin cancer, Neurological dysfunction

Front 111

What is sex linked inheritance?

Back 111

Genetic trait transmitted through X chromosome aka X linked

Front 112

Is X linked character transmitted from father to son?

Back 112

No because the gene present in the X chromosome gives its expression no matter Dom or Rec.

Only mother to son

Front 113

What is X-Chromosome inactivation
?

Back 113

In each somatic cell of women only one X chromosome is transcriptionally active.
Whereas the second X chromosome is almost transcriptionally inactive and exists in the form of heterochromatin
This inactive chromosome constitutes Barr body in the female somatic cells

Front 114

How is the number of barr bodies calculated?

Back 114

# of barr bodies = # of X chromosomes-1

Front 115

i) If the pattern is XX No. of barr body
ii) If the pattern is abnormal, eg. XXX;
iii) If the pattern is XO (Turner’s syndrome)

Back 115

i) If the pattern is XX No. of barr body 2-1 = 1

ii) If the pattern is abnormal, eg. XXX;
No. of barr body 3-1 = 2

iii) If the pattern is XO (Turner’s syndrome)
No. of barr body 1-1 = 0

Front 116

What is the mechanism of inactivation of an X chromosome?

Back 116

Involves DNA methylation. This results in the formation of transcriptionally inactive genes in chromosomes.

Front 117

What is the inactivation centre?

Back 117

It is presumed that proximal part of long arm (q) of X chromosome take part in barr body formation.

Evidences: In abnormal chromosome that
lacks q arm, no barr body is formed.

Front 118

What deterines X inactivation centre?

Back 118

The X inactivation centre contains an unusual gene XIST, which is supposed to play a key role in X inactivation

This XIST gene is transcriptionally silent in the active X chromosome but expressed (transcriptionally active) in inactive X chromosome

Front 119

Where are transcriptionally active genes located?

Back 119

mainly in Pseudoautosomal region of inactive X chromosome

Front 120

What are the genes that are carried by the y chromosome known as?

Back 120

Holandric genes

Front 121

Where is the SRY gene located and what does it code for?

Back 121

SRY gene located at its p arm. It codes for testis determining factor (TDF)

Front 122

What does mutated AZF gene cause?

Back 122

AZF genes, the mutation of which leads to azoospermia & oligospermia

Front 123

What are some X-linked recessive disorders?

Back 123

A number of well known diseases are caused by X-Linked Recessive Genes. These include
Hemophilia A,
Duchenne Muscular Dystrophy
Glucose 6 phosphate dehydrogenase deficiency
Red – Green Color Blindness.

Front 124

Due to the presence of 2 copies of X chromosomes, females can exhibit how many types for X- Linked Inheritance?
Ex. Hemophilia

Back 124

Due to the presence of 2 copies of X chromosomes, females can exhibit 3 types of genotypes for X- Linked Inheritance

HH=homo normal
Hh=heter
hh=affected

Front 125

What is the incidence of Duchenne Muscular Dystrophy? Features? What is elevated? How is it caused?

Back 125

Incidence: Approx.1/3500 male births

Progressive myopathy, muscle weakness

Elevated creatine kinase level in plasma

Caused by mutation in DMD gene that codes for a protein called as Dystrophin.

DELETION

Front 126

What causes hemophilia A & B? What is the incidence?

Back 126

Caused due to mutation of 2 separate genes

Incidence:
Hemophilia A – 1/5000 to 1/10,000 in male birth
Hemophilia B-1/100,000, comparatively rare

Front 127

What does Hemophilia A affect? What factor is defctive in Hemophilia B?

Back 127

Hemo A affects Clotting Factor VII

Factor IX is defective in Hemo B

Front 128

What causes Fragile X syndrom? What type of genetic complication is this? What is characteristic?

Back 128

Another example for abnormal unstable trinucleotide repeat expansion

Also an example for Somatic mosaicism

Characterized by mental retardation

Front 129

What is Vitamin D resistant Rickets? Where is the defect?

Back 129

Familial hypophosphatemia

Defect in renal tubular resorption of phosphate

Presents in 1st year of life with progressive limb deformities, growth retardation, and rickets

Front 130

What is Rett Syndrome?

Back 130

Occurs almost exclusively in females
Lethal in males
Severe neurological manifestations

Front 131

What is Mosaicisim?

Back 131

It is a pattern in which the cells of an individual or a tissue are derived from a single zygote but from more than a single genetically distinct cell line.

Front 132

When is mosaicism caused?

Back 132

Mutation during embryonic development is responsible for mosaicism


Mosaicism may be observed in either somatic cells or germline cells and is probably responsible for many unusual phenotypic observations.

If the mutation occurs prior to the separation of germline cells from somatic cells, the effect is seen in both the somatic and germline cells

Front 133

What is Somatic Mosaicism?

Back 133

Mutation occurring on somatic cells during embryonic development

May be manifested as a segmental patchy abnormality

Front 134

What is Germline Mosaicism? Where is mutation?

Back 134

Appearance of a new autosomal dominant mutation in more than one member in a sibship could be due to Gemline Mosaicism

Due to mutation in germline cells of the parent (male or female) the defect is subsequently passed into the offspring. Here the parent with germline mosaicism is phenotypically normal

Front 135

When does genomic imprinting take place?

Back 135

The Genomic Imprinting takes place during gametogenesis, before fertilization

Front 136

What is uniparental disomy? What is isodisomy?
What is Heterodisomy?

Back 136

It is a pattern where a cell contains two chromosomes derived from one parent.

If identical chromosome is present in duplicate --- Isodisomy

If both homologous chromosomes from one parent are present ---- Heterodisomy.

Front 137

How many kb does Mitochondrial DNA have? How many genes? What do those genes cod for?

Back 137

Circular, containing about 16.5 Kb.

Each mt.DNA contains 37 Genes

22 genes code for tRNA, 2 for rRNA and 13 for polypeptides that comprise enzymes of Oxidative Phosphorylation system

Front 138

How many mt. DNA do most cells contain?

Back 138

at least 1000

Front 139

Where do we get out mitochondrial DNA from?

Back 139

MOTHER only

Front 140

What is Homoplasmy? What is heeteroplasmy?

Back 140

Homoplasmy: A daughter cell gets either pure normal mt.DNA or mutated mt.DNA

Heteroplasmy: A daughter cell gets both normal and mutated mt.DNA

Front 141

What does the term mitochondrial genetic bottle neck mean?

Back 141

In females the total number of mitochondria is reduced considerably in premature oocytes and then suddenly amplifies in mature oocytes. This process is termed as mitochondrial ‘genetic bottle neck’

Front 142

What is affected by mutation of mt.DNA? What is an example? What are the symptoms?

Back 142

Mutation of mt.DNA generally affects those tissues that need intact oxidative phosphorylation.

Especially Neuromuscular tissues

Common Clinical symptoms: Myopathy, encehalopathy, Ataxia, Retinal degeneration and Loss of function of external ocular muscles.

Front 143

What are examples of disorder caused due to mutation in mt.DNA?

Back 143

1. Leber Hereditary Optic Neuropathy: Homoplasmic pattern, Symptoms are – Rapid optic nerve death and Blindness

2. Mitochondrial encephalomyopathy, lactic acidosis and stroke (MELAS):
Heteroplasmic pattern, Symtoms are ….