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Disease Mechanisms > Genetics - Genetic Inheritance > Flashcards

Genetics - Genetic Inheritance Flashcards

1
Q

In which direction is DNA replicated and read?

A

5’ to 3’ direction

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2
Q

What forms the backbone of DNA?

A

2-deoxyribose

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3
Q

What forms the backbone of RNA?

A

ribose

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4
Q

What are the bases in DNA?

A

ACGT

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5
Q

What are the bases in RNA?

A

ACGU

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6
Q

How do the bases pair in DNA?

A

A - T

G - C

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7
Q

What is a chromosome?

A

DNA stand wound with histones

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8
Q

How can damage during replication cause disease?

A

DNA can be damaged during replication

Usually fixed by repair mechanisms

Defects in repair mechanism cause disease

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9
Q

What is mitosis?

A

Division of diploid parent cell into two identical diploid daughter cells

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10
Q

What is meiosis?

A

Division of one diploid parent cell into 4 heterogenous haploid daughter cells

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11
Q

Describe meosis.

A

DNA replication and recombination

First round of division into two diploid cells

Second round of division into 4 haploid cells

Recombination introduced genetic variation

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12
Q

What is the difference in structure between RNA and DNA?

A

DNA = double stranded

RNA = single stranded

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13
Q

What is an exon?

A

Coding portion of a gene

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14
Q

What is an intron?

A

Non-coding portion of a gene

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15
Q

What is the high level architecture of a gene?

A

Promoter

Exons & Introns

Stop Codon

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16
Q

What are the processes requires to create a protein from DNA?

A

Transcription

Splicing

resulting in mRNA

Translation

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17
Q

How is the amount of protein produced determined?

A

Rate of transcription to pre-mRNA

Rate of splicing to mRNA

Half-life of mRNA

Rate of processing of polypeptide

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18
Q

How many bases encode an amino acid?

A

3

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19
Q

How are polymorphisms in the human genome defined?

A

A variation that has a population frequency of greater than 1%

of

A variation that does not cause a disease in its own right (although it may predispose to a common disease)

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20
Q

How is a mutation defined?

A

A gene change causing a genetic disorder

or

Any heritable change in the genome

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21
Q

What is the difference between classical genetic disease and multifactorial diseases?

A

Classical genetic disease

one mutation is sufficient to cause disease

Multifactorial disease

multiple polymorphisms cause a risk of disease

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22
Q

What process is necessary to allow DNA to be transcribed?

A

DNA has to be unpacked

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23
Q

What is the normal karyotype?

A

46 XX

46XY

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24
Q

What are the parts of a chromosome?

A

Telomere

Short arm

Centromere

Long Arm

Telomere

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25
Q

How can individual chromosomes be recognized?

A

Banding pattern with specific stains

Length

Position of centromere

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26
Q

What are acrocentric chromosomes?

A

Ones in which the short arm only contains satelite ribosomal genes, tRNAs etc

Only the long arm is really important

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27
Q

What is the difference between balanced and unbalanced chromosome rearrangement?

A

In balanced chromosomal arrangement all chromosomal material is present

In unbalanced chromosomal rearrangement there is either extra or missing chromosomal material, mostly commonly 1 or 3 copies of part of the genome

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28
Q

What is aneuploidy?

A

A whole extra or missing chromosome

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29
Q

What is translocation?

A

Rearrangement of chromosomes

30
Q

What is the karotype of trisomy 21 (Down Syndrome)?

A

47 XY +21

47 XX +21

31
Q

What is a Robertsonian Translocation?

A

When two acrocentric chromosomes are stuck end to end

32
Q

What are the possible genotypes of the offspring of a normal father and a mother with a Robertsonian translocation?

A

Normal

Balanced translocation

Trisomy 14 - miscarriage

Trisomy 21 - Down Syndrome

33
Q

What are the probabilites of having a second child with Down Syndrome?

A

Primary trisomy 21 - 1%

Robertson translocation - higher

34
Q

What condition is caused by Trisomy 18

A

Edward Syndrome

35
Q

What condition is caused by 45X karotype?

A

Turner syndrome

36
Q

Why is X chromosome aneuploidy better tolerated?

A

Because of X inactivation

37
Q

Which condition results from the karotype 47 XXY?

A

Klinefelter syndrom

38
Q

What are the reproductive risks of reciprocal translocations?

A

50% normal chromosome or balanced translocation

large unbalanced segments - miscarriage

small unbalanced segments - dysmorphic delayed child

39
Q

What is FISH used for?

A

Detect certain segments of DNA on chromosomes

40
Q

What type of mutation leads to DiGeorge syndrome?

A

Deletion

(22q11)

41
Q

What role does the HER2 gene play in breast cancer?

A

It is an oncogene.

HER2 amplification can lead to an aggressive form of breast cancer.

42
Q

What molecular technique can be used to look a specific loci or chromosomes?

A

Quantitative PCR

43
Q

How do you investigate whether a genetic variation is a polymorphism or a mutation?

A

Is it de-novo?

Has it been reported before?

What genes does it delete?

44
Q

What is the first line chromosome test?

A

Array CGH

45
Q

What is somatic mosaicism?

A

When different populations of cells (in different tissue or organs) are genetically distinct.

This occurs if recombination occurs during mitosis.

46
Q

Give two examples of conditions where gonadal mosaicism is involved.

A

Duchenne muscular dystrophy

Osteogenesis imperfecta

47
Q

What type of genes are involved in cancer?

A

Tumour supressor genes

(stop cells dividing)

Oncogenes

(start cells dividing)

48
Q

What treatment would be used for HER2 amplification?

A

Trastuzamab

49
Q

What treatment would be given for Philadelphia Chromosome (chronic myelogenous leukemia)?

A

Imatinib

50
Q

What is penetrance?

A

The likelihood of having a disease if you have a gene mutation

51
Q

What are Mendelian Disorders?

A

Diseases predominantly caused by a change in a single gene

52
Q

What gene changes can lead to disease?

A

Chromosome aneuploidies

Chromosomal insertions/deletions

Subtle chromosome abnormalities

Changes in gene sequence

Insertion or deletion of a few bases

Change of a single base

53
Q

What is the effect of a mutation on the promoter sequence

A

No transcription or reduced transcription

resulting in

no or reduced protein

54
Q

What is the effect of a mutation that alters the splice consensus?

A

Absent or abnormal protein

55
Q

What is the result of a base change introducing a new stop codon?

A

Absent or short protein

56
Q

What is the result of a base change altering the amino acid sequence?

A

Different or non-functional protein

57
Q

What are the types of mutation in DNA sequences?

A

Wild type

Stop

Missense

Insertion

Deletion - out of frame

Deletion - in frame

Triplet expansion

58
Q

Is a genetic disease always caused by the same mutation?

A

No.

Mutations in several genes may cause the same disease.

59
Q

What are the features of autosomal dominant inheritance?

A

Disease is seen in all generations

50% risk of affected child

Males and females equally likely to be affected

Variable disease severity

60
Q

How do mutations cause disease?

A

Haploinsufficiency

having one working copy of the gene is not enough

Dominant negative

Abnormal protein interferes with normal protein

Gain of function

Mutation activates genes

Loss of heterozygosity

61
Q

What are the features of autosomal recessive inheritance?

A

Two faulty copies of the gene required to cause disease

Often only one generation affected

1 in 4 risk of affected child if parents are carriers

Increased likelihood in consanguinous families

Usually cause loss of function

62
Q

What is the inheritance of phenylketonuria?

A

Autosomal recessive

63
Q

What are the features of X-linked rescessive inheritance?

A

If the mother is the carrier:

Female progeny will be normal or carrier

Male progeny will be normal or affected

If the father is the carrier:

All of male children will be normal (no male to male transmission)

All female children will be carriers

64
Q

Why might a female carrier of an X-linked recessive disease show mild symptoms of the disease?

A

Skewed X Inactivation

In female cells, only one X chromosome is active

On average, half the cells have the working gene, and half have the affected gene, but this may beome skewed

65
Q

How do twin studies inform genetics?

A

For a disease with a genetic contribution you would expect a monozygotic twin to be affected more frequently than a dizygotic twin

66
Q

Give examples of 3 non-Mendelian inheritance patterns

A

Epigenetic modification of DNA

Mitochondrial inheritance

Somatic mosaicism

67
Q

What is the clinical importance of methylation?

A

DNA methylation usually occurs on C bases, just before G bases and represses transcription

Methylation causes gene silencing in cancer

It is a mechanism by which the environment affects gene expression

(e.g. starvation during pregnancy)

68
Q

What is imprinting?

A

Differences in gene expression depending on whether a gene is maternally or paternally inherited

69
Q

What is Angelman’s syndrome?

A

Disorder of the UBE3A gene on chromosome 15

UBE3A only works in maternal copy (paternal copy is methylated)

It can occur if both copies of chromosome 15 are inherited from the father, or if there’s a new mutation in the maternal copy.

70
Q

What are the features of mitochondrial inheritance?

A

Rare

Maternal transmission only

Male and female children equally affected

Disease Mechanisms (9 decks)

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