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Y2 GENETICS IN MEDICINE > Intro & Gene Anatomy > Flashcards

Intro & Gene Anatomy Flashcards

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1
Q

What is meant by ‘human genetics’?

A

The mechanisms of inheritance and variation in humans

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2
Q

What is meant by ‘medical genetics’?

A

the subset of human genetics that is important in medicine and research

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3
Q

What is meant by ‘molecular genetics’?

A

the study of the structure and function of individual genes

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4
Q

What is meant by ‘clinical genetics’?

A

the application of genetics to diagnosis and patient care

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5
Q

What is the difference between genotype and phenotype?

A

Genotype is what is written in the genetic code

Phenotype is the way in which the genotype manifests itself in physical signs, disease or observable characteristics

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6
Q

What are the typical genetic abnormalities seen in children?

A
  1. birth anomalies
  2. dysmorphic features
  3. learning difficulties
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7
Q

What are the 4 typical things in adults that would be covered under clinical genetics?

A
  1. diagnosis of genetic disorders
  2. predictive testing
  3. carrier testing
  4. looking at family histories
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8
Q

Why might a pregnant woman be referred to clinical genetics?

A
  1. if there is a known genetic disorder
  2. abnormality detected on routine ultrasound screening
  3. fetal loss or recurrent miscarriages
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9
Q

What are the 3 stages in making a genetic diagnosis?

A
  1. creating a family tree to detect a pattern of inheritance
  2. clinical examination to define the phenotype
  3. diagnostic tests
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10
Q

What are the 2 categories of tests that are used for genetic disorders?

A
  1. non-genetic tests e.g. x-rays

2. genetic tests

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11
Q

What are the 4 types of genetic testing?

A
  1. diagnostic testing
  2. predictive testing
  3. carrier testing
  4. prenatal testing
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12
Q

What is prenatal testing and why is it necessary?

A

Testing fetal DNA during pregnancy

Can lead to termination of pregnancy and prevention of genetic disease

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13
Q

What are the 3 main advantages of genetic testing?

A
  1. allows for early diagnosis
  2. carrier testing allows for reproductive choices
  3. prenatal testing allows for reproductive choices
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14
Q

What is the main disadvantage of genetic testing?

A

The knowledge of knowing that you are likely to get a certain condition can affect life in other ways

e.g. no cure for Alzheimers, can affect insurance prospects

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15
Q

What is meant by pharmacogenetics?

A

Studying an individual’s genetic make up in order to predict responses to a drug and guide prescription

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16
Q

What is meant by pharmacogenomics?

A

Analysing entire genomes across groups of individuals to identify genetic factors influencing responses to a drug

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17
Q

How many nucleotides are in the genome?

A

3 x 10^9 nucleotides per haploid genome

humans receive 1 haploid genome from the mother and 1 from the father

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18
Q

What molecule makes up the backbone of DNA?

A

2’-deoxyribose

it has no hydroxyl group on the second carbon

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19
Q

What is the main difference between DNA and RNA and why is it significant?

A

RNA has a hydroxyl group on the second carbon

This means RNA is transient (less stable) as the phosphodiester bond breaks more easily

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20
Q

In which direction are DNA sequences written and why?

A

5’ to 3’ direction

this is the direction in which DNA and RNA are synthesised

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21
Q

How do the different nucleotides pair and how many hydrogen bonds do they form?

A

A and T pair by 2 hydrogen bonds

C and G pair by 3 hydrogen bonds

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22
Q

How are DNA sequences written in shorthand?

A

Only one DNA sequence is written, even though there are 2 strands in the double-stranded molecule

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23
Q

What is the sense strand and why is it significant when writing DNA sequences in shorthand?

A

The sense strand is written in shorthand

This is the strand that ends up in the mRNA

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24
Q

What is the difference between ‘base pair’ and ‘nucleotide’?

A

They mean the same thing and are used interchangeably

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25
Q

What happens in DNA replication as the replication fork migrates upwards?

A
  1. the parent strands run in opposite directions
  2. as DNA can only be synthesised 5’-3’, only one strand is synthesised continuously
  3. the other strand is synthesised backwards in discontinuous fragments (Okazaki fragments)
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26
Q

What happens to the Okazaki fragments after replication?

Why is this significant?

A

They are stitched together after replication to make a daughter strand

This means the process is susceptible to errors

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27
Q

Approximately how long is a length of DNA?

How long is a chromosome?

A

Naked DNA in 1 chromosome is 9 cm long

A chromosome is 9 micrometers long

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28
Q

Where is the information stored within a chromosome?

A

Most information is written in the DNA

Some is written in modifications of the proteins that form the histone core

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29
Q

What is meant by ‘diploidy’?

A

There are 2 copies of each chromosome

1 is maternal and 1 is paternal

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30
Q

What would a karyotype for Klinefelter syndrome show?

A

2 X chromosomes and 1 Y

This is abnormal as there are 47 chromosomes

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31
Q

What is significant about the centromere?

A

It is where the chromosomes attach to the spindle during cell division

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32
Q

What are telomeres?

What are the 2 types?

A

They are the ends of the chromosome

Ptel and Qtel correspond to the p and q arms

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33
Q

What are the p and q arms of a chromosome?

A

p is the short arm

q is the long arm

34
Q

What is significant about the telomere?

How does this affect the chromosome?

A

Due to the discontinuous replication process, the telomere cannot be copied

The end of the chromosome cannot be replicated

35
Q

What is the telomeric repeat sequence?

A

TTAGGG

36
Q

What is the role of telomerase?

A

It adds the telomeric repeat sequence to the end of the chromosome

37
Q

In which cells is telomerase active?

A

It is active in germ cells and cancer cells

It is inactive in somatic cells

38
Q

What is the result of telomerase being inactive in somatic cells?

A

telomeres shorten with somatic cell division

this means there is a finite number of cell divisions before senescence

39
Q

What is meant by the ‘chromosome ideogram’?

A

There are a number of bands visible on a chromosome

The number of bands depends on how stretched out the chromosome is

40
Q

What are the 2 versions of chromosome coordiantes?

A

2009 and 2013

Genetic reports must specify which version of the reference genome is used

41
Q

Why can chromosomes have coordinates?

A

DNA in the chromosome is linear

This means nucleotides can be numbered

42
Q

What is the difference between n and 2n?

A

n = 23

2n = 46

2n is the diploid chromosome content

43
Q

What is meant by ‘dosage’?

A

the number of copies of a particular gene present

44
Q

What is haploinsufficiency?

A

when someone is haploid for a particular gene

this is insufficient as 2 copies of every gene are needed

45
Q

What is the difference in the amount of genes carried on the X and Y chromosomes?

A

X chromosome contains many genes and information

The Y chromosome only shares a few genes with the X chromosome

It is smaller and contains fewer genes

46
Q

What is meant by ‘pseudoautosomal regions’?

A

Regions which contain information that is shared between the X and Y chromosome

47
Q

Why are males described as hemizygous?

A

They have only one copy of many of the genes present on the X chromosome

48
Q

What is the one gene present on the Y chromosome, but not the X?

A

SRY gene

This is the sex-determining region and specifies development of testis

This leads to male traits

49
Q

How are chromosomes numbered?

A

They are numbered from the largest to the smallest

50
Q

Around how much DNA is present in 1 haploid genome?

How much of this is coding?

A

3,000 Mbp dsDNA per haploid genome

> 90% is non-coding DNA

51
Q

How many protein-coding genes are there in the genome?

A

20,000

52
Q

What is significant about the mitochondrial genome?

How many genes does it contain?

A

It is circular rather than linear

It has 16,000 nucleotides and contains 37 genes

53
Q

What is significant about how mitochondria are inherited?

A

All the mitochondria come from the mother

All mitochondrial pathologies are maternally inherited

54
Q

What are the 2 different sequence classes in the human genome?

A
  1. single-copy sequences

these are non-repetitive

  1. repetitive sequences
55
Q

What are the 2 types of repetitive sequences?

A
  1. interspersed repeats

2. satellite DNA

56
Q

What is meant by satellite DNA?

A

Large blocks of repetitive sequence chunked together

e.g. heterochromatin

57
Q

What is the definition of a gene?

A

They are functional units of DNA

They are expressed

58
Q

What are the processes that genes go through to be expressed?

A
  1. transcription - copying into RNA

2. translation - turning RNA into protein or functional RNA

59
Q

What are the 3 components of genes?

A
  1. exons
  2. introns
  3. regulatory sequences
60
Q

What is the difference between introns and exons?

A

Exons are copied into the mRNA

Introns are spliced out and not in the mRNA

61
Q

What is significant about the sequence of every intron?

A

They start with GT

They end with AG

62
Q

How can 20,000 genes create 100,000 different proteins?

A

Exons are spliced together in different orders to make mRNA that differs from each other

63
Q

What is meant by exon skipping?

A

An exon may be excluded from a gene to create 2 alternative proteins

64
Q

How does evolution of genes progress?

What does this lead to?

A

Duplication and divergence

This means most genes belong to a family of structurally related genes

65
Q

What are the 3 stages in gene evolution?

A
  1. there is one ancestral gene
  2. the gene is duplicated to give 2 tandemly arranged identical genes
  3. Mutations over millions of years lead to the 2 copies diverging in sequence and performing different functions
66
Q

What are pseudogenes?

A

They look like copies of normal genes but contain errors which mean they are non-functional

67
Q

When can pseudogenes become a problem?

A

They can interfere with functions of the proper gene

They can be difficult to tell apart from the parent gene

68
Q

Why are pseudogenes formed?

A

Genes accumulate mutations that inactivate them as they are no longer needed

69
Q

What are processed genes?

A

Intronless copies of other genes

They look like a parent gene with the introns removed

70
Q

How are processed genes formed?

A

Through reverse transcription and reintegration into parent DNA

71
Q

What happens to most processed genes?

A

They become inactive processed pseudogenes

72
Q

What is the difference between satellite DNA and interspersed repeats?

A

satellite DNA contains large blocks of repetitive DNA sequence

interspersed repeats are scattered around the genome

73
Q

Where does satellite DNA tend to be found?

A

In large blocks at centromeres and heterochromatic chromosomal regions

74
Q

What is significant about alphoid DNA?

A

It is a form of satellite DNA that is found in centromeres

It is chromosome-specific

75
Q

How can satellite DNA be polymorphic?

A

It means different people’s chromosomes look different due to different quantities of junk DNA being present

76
Q

How many base pairs are found in alphoid DNA?

A

It is a 171-bp repeat unit

77
Q

What is alphoid DNA used for?

A

It is required for the assembly of the centromere

78
Q

Where may interspersed repeats be found?

A

They are scattered around the genome

Individual copies are present at many locations

This may be between or within genes

79
Q

What is a SINE?

A

Short interspersed nuclear element

80
Q

What is the Alu repeat an example of?

How is it dispersed and how long is it?

A

it is a SINE

It is 300 bp long

It is dispersed by retrotransposition (reverse transcription)

Y2 GENETICS IN MEDICINE (11 decks)

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