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Y2 GENETICS IN MEDICINE > Intro & Gene Anatomy > Flashcards

Intro & Gene Anatomy Flashcards

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
What happens in DNA replication as the replication fork migrates upwards?
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)
26
What happens to the Okazaki fragments after replication? Why is this significant?
They are stitched together after replication to make a daughter strand This means the process is susceptible to errors
27
Approximately how long is a length of DNA? How long is a chromosome?
Naked DNA in 1 chromosome is 9 cm long A chromosome is 9 micrometers long
28
Where is the information stored within a chromosome?
Most information is written in the DNA Some is written in modifications of the proteins that form the histone core
29
What is meant by 'diploidy'?
There are 2 copies of each chromosome 1 is maternal and 1 is paternal
30
What would a karyotype for Klinefelter syndrome show?
2 X chromosomes and 1 Y This is abnormal as there are 47 chromosomes
31
What is significant about the centromere?
It is where the chromosomes attach to the spindle during cell division
32
What are telomeres? What are the 2 types?
They are the ends of the chromosome Ptel and Qtel correspond to the p and q arms
33
What are the p and q arms of a chromosome?
p is the short arm q is the long arm
34
What is significant about the telomere? How does this affect the chromosome?
Due to the discontinuous replication process, the telomere cannot be copied The end of the chromosome cannot be replicated
35
What is the telomeric repeat sequence?
TTAGGG
36
What is the role of telomerase?
It adds the telomeric repeat sequence to the end of the chromosome
37
In which cells is telomerase active?
It is active in germ cells and cancer cells It is inactive in somatic cells
38
What is the result of telomerase being inactive in somatic cells?
telomeres shorten with somatic cell division this means there is a finite number of cell divisions before senescence
39
What is meant by the 'chromosome ideogram'?
There are a number of bands visible on a chromosome The number of bands depends on how stretched out the chromosome is
40
What are the 2 versions of chromosome coordiantes?
2009 and 2013 Genetic reports must specify which version of the reference genome is used
41
Why can chromosomes have coordinates?
DNA in the chromosome is linear This means nucleotides can be numbered
42
What is the difference between n and 2n?
n = 23 2n = 46 2n is the diploid chromosome content
43
What is meant by 'dosage'?
the number of copies of a particular gene present
44
What is haploinsufficiency?
when someone is haploid for a particular gene this is insufficient as 2 copies of every gene are needed
45
What is the difference in the amount of genes carried on the X and Y chromosomes?
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
What is meant by 'pseudoautosomal regions'?
Regions which contain information that is shared between the X and Y chromosome
47
Why are males described as hemizygous?
They have only one copy of many of the genes present on the X chromosome
48
What is the one gene present on the Y chromosome, but not the X?
SRY gene This is the sex-determining region and specifies development of testis This leads to male traits
49
How are chromosomes numbered?
They are numbered from the largest to the smallest
50
Around how much DNA is present in 1 haploid genome? How much of this is coding?
3,000 Mbp dsDNA per haploid genome >90% is non-coding DNA
51
How many protein-coding genes are there in the genome?
20,000
52
What is significant about the mitochondrial genome? How many genes does it contain?
It is circular rather than linear It has 16,000 nucleotides and contains 37 genes
53
What is significant about how mitochondria are inherited?
All the mitochondria come from the mother All mitochondrial pathologies are maternally inherited
54
What are the 2 different sequence classes in the human genome?
1. single-copy sequences these are non-repetitive 2. repetitive sequences
55
What are the 2 types of repetitive sequences?
1. interspersed repeats | 2. satellite DNA
56
What is meant by satellite DNA?
Large blocks of repetitive sequence chunked together e.g. heterochromatin
57
What is the definition of a gene?
They are functional units of DNA They are expressed
58
What are the processes that genes go through to be expressed?
1. transcription - copying into RNA | 2. translation - turning RNA into protein or functional RNA
59
What are the 3 components of genes?
1. exons 2. introns 3. regulatory sequences
60
What is the difference between introns and exons?
Exons are copied into the mRNA Introns are spliced out and not in the mRNA
61
What is significant about the sequence of every intron?
They start with GT They end with AG
62
How can 20,000 genes create 100,000 different proteins?
Exons are spliced together in different orders to make mRNA that differs from each other
63
What is meant by exon skipping?
An exon may be excluded from a gene to create 2 alternative proteins
64
How does evolution of genes progress? What does this lead to?
Duplication and divergence This means most genes belong to a family of structurally related genes
65
What are the 3 stages in gene evolution?
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
What are pseudogenes?
They look like copies of normal genes but contain errors which mean they are non-functional
67
When can pseudogenes become a problem?
They can interfere with functions of the proper gene They can be difficult to tell apart from the parent gene
68
Why are pseudogenes formed?
Genes accumulate mutations that inactivate them as they are no longer needed
69
What are processed genes?
Intronless copies of other genes They look like a parent gene with the introns removed
70
How are processed genes formed?
Through reverse transcription and reintegration into parent DNA
71
What happens to most processed genes?
They become inactive processed pseudogenes
72
What is the difference between satellite DNA and interspersed repeats?
satellite DNA contains large blocks of repetitive DNA sequence interspersed repeats are scattered around the genome
73
Where does satellite DNA tend to be found?
In large blocks at centromeres and heterochromatic chromosomal regions
74
What is significant about alphoid DNA?
It is a form of satellite DNA that is found in centromeres It is chromosome-specific
75
How can satellite DNA be polymorphic?
It means different people's chromosomes look different due to different quantities of junk DNA being present
76
How many base pairs are found in alphoid DNA?
It is a 171-bp repeat unit
77
What is alphoid DNA used for?
It is required for the assembly of the centromere
78
Where may interspersed repeats be found?
They are scattered around the genome Individual copies are present at many locations This may be between or within genes
79
What is a SINE?
Short interspersed nuclear element
80
What is the Alu repeat an example of? How is it dispersed and how long is it?
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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