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Essential Medical Science (UoL, Medicine) > Clinical Genetics - Basics > Flashcards

Clinical Genetics - Basics Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

What three factors govern the balance of genetic and environmental factors for any condition?

A

100% Environmental
Polygenic
Single Gene

(represented as a triangle with environmental at the top)

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2
Q

What is achondroplasia?

A

Achondroplasia is a common cause of dwarfism, caused by a mutation in fibroblast growth factor receptor 3 (FGFR3)

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3
Q

What are the characteristics of a purely genetic cause of disease?

A

Rare
Simple genetics
Unifactorial
High recurrence rate

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4
Q

What are the characteristics of environmental cause of disease?

A

Common
Complex genetics
Multifactorial
Low recurrence rate

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5
Q

What categories are genetic disorders classified into?

A 
Multifactorial/Complex
Single Gene
Chromosomal
Mitochondrial
Somatic Mutations
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6
Q

Define multifactorial/complex genetic disorders

A

Interaction of multiple genes in combination with environmental factors

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7
Q

Define single gene disorders

A

A mutation in a single gene

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8
Q

Define chromosomal genetic disorders

A

An imbalance or rearrangement in chromosome structure i.e. aneuploidy

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9
Q

Define mitochondrial genetic disorders

A

Due to mutations in the mitochondria DNA

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10
Q

Define somatic mutations

A

Mutations with a gene in a defined population of cells that results in disease

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11
Q

What are the 4 single gene modes of inheritance?

A

Autosomal Dom
Autosomal Rec
X-Linked
Mitochondrial

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12
Q

How many chromosomes are there?

A

46 in 23 pairs

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13
Q

What are the characteristics of gametes?

A

Contain 23 chromosomes with 1 copy of each gene

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14
Q

What would the following nomenclature mean about the patient?

AA

A

Healthy patient with 2 normal genes

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15
Q

What would the following nomenclature mean about the patient?

Aa

A

Healthy person with 1 normal copy and 1 gene copy with the disease mutation i.e. carrier

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16
Q

What are some characteristics of AD Inheritance?

A

A trait or disease runs from one generation to the next

Males and females are equally affected

Offspring of affected person has a 50% (1in2) chance of inheriting the mutation

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17
Q

What type of inheritance does the following relate to?

‘Affected individuals are heterozygous for the mutation

A

Autosomal Dominant

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18
Q

What type of inheritance does the following relate to?

‘Chance that the offspring affected = 50%’

A

Autosomal Dominant

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19
Q

What is ‘Penetrance?’

A

The frequency with which a specific genotype is expressed by those individuals that possess it, usually given as a percentage

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20
Q

What is incomplete penetrance?

A

Not all relatives who inherit the mutation develop the disorder

21
Q

What is ‘Expressivity’

A

Variation in expression - the extent to which a heritable trait is manifested by an individual

22
Q

What is ‘Anticipation’

A

The symptoms of a genetic disorder become apparent at an earlier age as it is passed fro one generation to the next

23
Q

What is a ‘new dominant/de novo mutation’

A

A new mutation that has occurred during gametogenesis or in early embryonic development

24
Q

What are some characteristics of AR inheritance?

A

Disease seen in one generation

Does not tent to pass from one generation to the next

Offspring of affected individuals has low risk of disease

Relatives may be asymptomatic carriers of the disease

M=F

Gene mutation, not chromosomes

25
Q

What type of inheritance does the following relate to?

‘Affected individuals are homozygous or compound heterozygous for the mutation’

A

AR Inheritance

26
Q

What type of inheritance does the following relate to?

‘Risk of offspring being affected = 25% (aa)’

A

AR Inheritance

27
Q

What type of inheritance does the following relate to?

‘Risk of offspring being carrier = 66%’

A

AR Inheritance

28
Q

Cystic Fibrosis

AR or AD?

A

AR

29
Q

Haemachomatosis

AR or AD

A

AR

30
Q

Sickle Cell Disease

AR or AD

A

AR

31
Q

Myotonic Dystrophy

AR or AD

A

AD

32
Q

Marfans

AR or AD

A

AD

33
Q

Huntington’s

AR or AD

A

AD

34
Q

What are some characteristics of XL inheritance?

A

Males primarily affected

Women may be unaffected to fully affected

Can not have male to male transmission

Gene mutations and chromosome deletions/duplications

35
Q

Duchenne Muscular Dystrophy

AR / AD/ XL ?

A

XL

36
Q

Fragile X Syndrome

AR / AD / XL

A

XL

37
Q

Red/Green colour blindness

AR / AD / XL

A

XL

38
Q

What type of inheritance does the following relate to?

1/4 normal girl + 1/4 carrier girl

1/4 normal boy + 1/4 affected boy

A

XL

39
Q

What type of inheritance does the following relate to?

All daughters carriers
All sons are unaffected

A

XL

40
Q

Why can females have such a variable phenotype?

A

Two main factors influencing expression of phenotype

X Inactivation
XL dominant VS XL recessive inheritance

41
Q

Can a female phenotype be predicted accurately on prenatal testing?

A

No

42
Q

What is X Inactivation?

A

The process of random inactivation of one of the X chromosomes in cells with more than one X chromosome

43
Q

What does X Inactivation do?

A

It compensates for the presence of the double x gene dose

44
Q

What are 4 characteristics of X Inactivation?

A

Is normal and occurs when there us 2 or more chromosomes in a cell

Occurs in early embryogenesis

Random as to which X is silenced

Once inactivated an X chromosome remains inactive for its lifetime and all its descendants

Most, but not all genes switched off on the inactivated X

45
Q

What is ‘skewed X inactivation?’

A

A random preference for ‘normal’ X chromosome to be inactivated

46
Q

What form of inheritance does the following condition have?

Rest syndrome
Fragile X

A

XL Dominant

47
Q

What form of inheritance does the following condition have?

Red green colour blindness
Haemophilia
Duchenes

A

XL Recessive

48
Q

When does mitochondrial inheritance occur?

A

When the sperm head carries no mitochondria

49
Q

What are some characteristics of mitochondrial inheritance?

A

Rare, males and females affected equally

Only 27 genes within mitochondrial DNA

Each cell has many mitochondria

Every mitocondrium has many copes of each gene

Mitochondria are inherited from the mothers egg

An affected mother will given all her children the mutation

Highly variable expressivity and therefore severity of phenotype between relatives

All the children of an affected man will be unaffected

Essential Medical Science (UoL, Medicine) (9 decks)

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