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Genetics > Genetics - Basics > Flashcards

Genetics - Basics Flashcards

1
Q

Where is genetic code contained

A

DNA
Bundled into chromosomes
Contained in nucleus

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2
Q

How many chromosomes

A

Comes in pairs so have two copies of each gene
23 pairs - 22 pairs and 1 sex
46 in total

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3
Q

What is one chromosome that is different

A

Sex chromosome
Male = XY
Female = XX

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4
Q

What is genotype

A

Genes that you have

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5
Q

What is phenotype

A

Physical expression of genes that we have

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6
Q

What is Mendelian inheritance

A

Some genes more dominant than other

Phenotype reflects more dominant gene

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7
Q

When does Mendelian occur

A

If disease is caused by single abnormal gene on non-sex chromosome

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8
Q

If autosomal dominant e.g. Huntington’s

A

Only need one copy of gene to be expressed in phenotype

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9
Q

If autosomal recessive e.g. CF

A

Need two copies of gene to have the phenotype

If have one copy = carrier

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10
Q

If both parents carrier of AR what is risk of

  • having disease
  • being a carrier
  • being normal
A

1 in 4 disease
2 in 4 carrier
1 in 4 normal

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11
Q

If one parent has AR disease and other is a carrier

A

2 in 4 carrier

2 in 4 has disease

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12
Q

Exam
Healthy parents
One sibling has single gene disease e.g. CF
2nd child does not
What is likelihood 2nd child is a carrier ?

A

Condition = AR as parents not affected but child is
Question is same as example 1
2nd child does NOT have disease
So 2 in 3 chance of being a carrier

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13
Q

What is risk of AD

A

Each child has 50% chance of inheriting mutation

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14
Q

X-linked recessive

A

Only males can get disease

Males cannot transmit as they give their Y chromosome

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15
Q

When do chromosomal abnormalities occur

Known as cytogenetic as can see under microscope

A

Structural abnormality
Translocation
Macro-deletion or insertion
Abnormal number

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16
Q

What is a deletion

A

Portion of chromosome missing

Very rare

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17
Q

What is a duplication

A

Portion chromosome duplicated so it contains twice the number of copies

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18
Q

Example

A

Charcot Marie Tooth

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19
Q

What is a translocation

A

Portion of one chromosome directly swapped with another

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20
Q

What is a reciprocal and how would it be picked up

A

Balanced
Two chromosomes swap a piece of genetic material
No material lost or gained
Usually healthy

Investigation of

  • Infertility
  • Recurrent miscarriage
  • Birth defects

Issue
- If child reeves unbalanced translocation may have too much of one chromosome and too little of another

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21
Q

Non-recipricol

A

No exchange

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22
Q

What does this cause

A

No specific syndrome
Predispose to other condition
Philadelphia translocation in AML - reciprocal of 9-22

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23
Q

What is trisomy

A

Person has extra chromosome so 3 copies of gene

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24
Q

Patau

A

Trisomy 13
Dysmorphia
LD
Rockerbottom

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25
Q

Edward

A

Trisomy 18

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26
Q

Down

A

Trisomy 21

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27
Q

What is Mitochondria

A 
Organelle inside cytoplasm 
Responsible for producing ATP for the cell
Contain own DNA
Vary depending on cell
Myocytes = thousands
Adipocytes = very few
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28
Q

What is mitochondria inheritance

A

Only mother contributes her mitochondrial DNA to zygote
Known as maternal inheritance
Proportion of DNA transferred determines whether affected

29
Q

Examples of mitochondrial disease

A 
Myopathy due to poor production of ATP
Deaf
Blindness
DM
Epilepsy
30
Q

What are potential reasons for genetic testing

A 
Diagnostic
Predictive
Carrier 
Other - forensic / paternity 
Susceptibility for common disorders may become possible
31
Q

What is diagnostic

A

Amniocentesis if a fetus

Testing for suspected genetic condition

32
Q

What is predictive

A

Done for single gene disorder that has implications in future e.g. BRCA1 or Huntington

33
Q

What is important to know

A

Penetrance

34
Q

What is carrier

A

Testing parents for gene that is AR to calculate risk to children

35
Q

What is essential ethics before testing

A

CONSENT
Genetic counselling
Discuss implications

36
Q

What type of tests

A

Karyotype
Microarray
Specific gene
DNA sequencing - only for research

37
Q

What is Karyotype

A

Looks at chromosomes - size, number and structure

Useful in Down / Turner

38
Q

What is Microarray

A

Used to screen for chromosomal abnormalities in common genetic conditions
Looks for mutations

39
Q

What are benefits of genetic testing

A 
Identify high risk
Identify non-carriers
Allow early detection and prevention
Releive anxiety over gene status
If -ve = concerns reduced
If +ve = plan for future, surveillance
40
Q

What are risks

A 
May not detect all mutations
Continued risk of sporadic disease 
Psychosocial harm
Economic harm - insurance / mortgage 
Removes hope
Known risk to offspring
41
Q

Why can adults be referred to genetic clinic

A 
Diagnostic testing
Predictive testing
Carrier testing
Cascade screen if one family member Dx
FH
Fetal loss or recurrent miscarriage
42
Q

What are the mechanism of adult onset of genetic disease

A

Single gene
Chromosomal
Mitochondrial
Multifactorial + environment

43
Q

What is continuum of penetrance

A

Likelihood of getting genetic disease associated with genetic variant
If don’t know penetrance then genetic testing to give prediction is difficult

44
Q

What do single gene disorders tend to have

A

High penetrance so risk estimation easier

45
Q

What about multifactorial disorder

A

Risk more difficult

46
Q

If testing what principles

A

Info must be used for prevention or RX
Counselling
Only test children if medical benefits as a child
Third parties have no access to results

47
Q

What do multi-factorial disease involve

A

Polygenetic

Environmental factors

48
Q

How does it involve multi-system

A

Several genes involved with diverse functions

Single gene widely expressed in different tissue

49
Q

What are common problems in multi-system disease

A

Variable expression
Present to large variety of specialist
FH easily missed

50
Q

Examples

A

DM
Haemochromatosis
TS
Neurofibroma

51
Q

How does trisomy 21 occur

A

Non-disjunction at meiosis

  • Gamete has extra copy of chromosome 21
  • When joins with normal = embryo with three copies of 21
  • Most common

Robertsonian translocation

  • Chromosome 21 joins with 14 (may be inherited from patient with balanced translocation)
  • Interferes with separation at meiosis

Mosaicism

  • Some cells of the individual have 3 copies of chromosome 21 and others have 2
  • Can be at such a low level don’t have symptoms
52
Q

What factors help determine risk of Downs in next baby

A

Maternal age
Previous child
Karyotype of parents
- Do they have Robertsonian translocation

53
Q

What would you write in referral letter to genetic clinic

A

No of miscarriage and how many weeks
Number live births
Karyotype result of both parents
Why you are referring e.g. counselling of their translocation

54
Q

How would a translocation be written

A

46 XY t(4:14)

55
Q

What are signs of unbalanced translocation

A

Learning difficulty

Early infant death

56
Q

How can you detect chromosomal abnormalities

A

Amniocentesis and send for CGH

57
Q

How do you interpret result

A

Look up on Unique website

58
Q

If family member found to have a translocation and sister pregnant?

A

Consent form has box to inform family
Test sister
If +Ve can do invasive testing

59
Q

What are 4 outcomes of gene coding

A

No mistake = functional protein
Mistake / variant but normal variant = functional
Mistake / variant part of disease = non functional
Mistake / variant not seen before = unsure

60
Q

What may a gene be reported as

A

FBN1 c566G>A pCys1889Tyr

FBN1 = gene with a variation 
c566GA = base swap at 566 G to A 
pCys1889Tyr = protein swap at 1889 Cysteine to Tyrosine
61
Q

How do you work out if variant has caused disease

A

Step 1
Can mutations in specific genes e.g. FBN1 cause clinical disease e.g. Marfan
- Put in database and find out

Step 2
Has specific variation been seen in someone with Marfan before
- Put in table

Step 3
Has the variation been seen in well person
- Put in table

Step 4
Does the mutation change the structure o the protein it is designed to produce

62
Q

If yes

A

Likely has disease

63
Q

What is a point mutation

A

Single base pair change

64
Q

What types of point mutations do you get

A

Silent = change doesn’t affect protein
Amino acid change = abnormal protein
Stop = truncated protein with no funtion

65
Q

What is the driver mutation

A

1st mutation to start process of malignancy

Important to know to see how disease develops / target therapy and monitor response

66
Q

What are hallmarks of malignant mutations

A 
Leads to dysregulated growth
Evasion of apoptosis
Likmitless replication
Sustained angiogenesis
Invasion and mets
67
Q

Is every cell in a tumour the same

A

No

Polyclonal as acquire cumulative changes

68
Q

AR conditions

A
  • Albinism
  • B thalassemia
  • CF
  • Deaf
  • Emphyesema due to A1At
  • Fredirecih ataxia
  • Glycogen storage
  • Haemochromatosis

Genetics (5 decks)

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