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Inheritance Flashcards

1
Q

What is a multifactorial condition

A

Disease that is due to a combination of genetic and environmental factors

Most common diseases are multifactorial

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2
Q

What are family studies

A

Compare the incidence of a disease amongst relatives of an affected individual with the general population

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3
Q

Family Studies

With risk for a multifactorial condition - fill in the gaps

  1. The risk of a condition in relatives of an affected individual is than the general population
A

Dramatically higher

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4
Q

What does proband mean

A

Individual affected with a disorder who is the first subject in a study (as of a genetic character in a family lineage)

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5
Q

What are the three ways of studying if a condition
has a genetic component

A

Family studies
Twin studies
Adoption studies

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6
Q

What does prevalence mean

A

How common a disease is in a given population

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7
Q

What does incidence mean

A

Onset of new cases in a given period of time

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8
Q

What are twin studies?

A

Compare genetically identical (MZ) with genetically non-identical (DZ) twins

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9
Q

What does concordance rate stand for?

A

% of twin pairs studies that both have the condition

Would expect it to be higher in monozygotic twins

Gives a rough figure for hereditability of a multifactorial disorder

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10
Q

What are adoption studies?

A

Adopted children of a parent with multifactorial condition have a higher risk of developing the disease

Higher in biological families only

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11
Q

Define hereditability

A

Proportion of the aetiology that can be ascribed to genetic factors as opposed to environmental factors

Expressed as a proportion of 1 or as a %

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12
Q

What is a way you can calculate hereditability

A

Concordance rate in monozygotic twins

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13
Q

Name the three characteristics of multifactorial inheritance

A
  1. The incidence of the condition is greatest amongst relatives of the most severely affected patients
  2. The risk is greatest for the first degree relatives and decreases rapidly in more distant relatives
  3. If there is more than one affected close relative then the risk for other relatives are increased
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14
Q

Define liability

A

When combine factors that influence the development of a multifactorial disorder, genetic and environmental

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15
Q

In the liability/threshold model which direction is the curve shifted in relatives compared to the normal population

A

Right

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16
Q

When the relationship is closer which direction does the curve shift in the liability/threshold model

A

Further to the right

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17
Q

What is the threshold marker in the liability/threshold model

A

Beyond this the abnormal phenotype is expressed

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18
Q

What is the definition for in the general population the proportion beyond the threshold (in the liability threshold model)

A

Population incidence

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19
Q

What is the definition for amongst relatives the proportion beyond the threshold (in the liability threshold model)

A

Familial incidence

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20
Q

What is the genome wide association studies

A

Utilises the fact genes can have several variants (alleles)

Compares the frequency of markers in a sample of patients and a sample of healthy controls

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21
Q

What would a pathogenic variation of a disease be

A

Variation in a gene which causes the gene to be inactivated or behave abnormally

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22
Q

Define polymorphisms

A

Genetic variation which still results in a functioning gene

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23
Q

What are the 4 environmental agents acting on embryogenesis

A
  1. Drugs and chemicals
  2. Maternal infections
  3. Physical agents
  4. Maternal illnesses
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24
Q

Name 4 post-natal environmental factors

A
  1. Type 2 diabetes - obesity
  2. Breast cancer - hormonal factors e.g. contraception
  3. Lung cancer e.g. smoking
  4. Schizophrenia e.g. recreational drugs
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25
What is the 3 underlying principles of genetics are deduced by Mendel
1. Segregation 2. Dominance 3. Independent assortment
26
What are the two types of mendelian inheritance
1. Autosomal and sex-linked 2. Dominant and recessive
27
What are the four types of non-mendelian inheritance
1. Imprinting 2. Mitochondrial inheritance 3. Multifactorial 4. Mosaicism
28
What are the three categories of genetic disorders
1. Chromosome abnormalities 2. Single gene disorders 3. Multi-factorial and polygenic disorders
29
Define autosome
Any chromosome, other than sex chromosomes, that occurs in pairs in diploid cells
30
Define recessive
Manifest only in homozygotes
31
Define allele
One or more alternative forms of a gene at a given location (locus)
32
Define homozygous
Presence of identical alleles at a given locus Homozygotes are affected
33
Define heterozygous
Presence of two different alleles at a given locus Heterozygotes are unaffected and are usually referred to as carriers
34
Define allelic heterogeneity
Different mutations within the same gene result in the same clinical condition
35
What are the three typical features of autosomal recessive inheritance
Male and females are affected on equal proportions Affect individuals only in a single generation Parents can be related (consanguineous)
36
How can you calculate risk of carriers
Chance mother is a carrier x chance dad is carrier x risk of affected child if both carriers Use population carrier frequency if risk is that of normal
37
Define consanguinity
Reproductive union between two relatives
38
Define autozygosity
Homozygosity by descent e.g. inheritance of the same altered allele through two branches of the same family
39
In autosomal recessive conditions what are the chance of carrier parents having affected offspring What are the chances of healthy siblings being carriers themselves
1 in 4 2 in 3
40
Define autosomal dominant inheritance
Disease manifest in the heterozygous state e.g. only one affected gene needed
41
What are the 3 typical features of autosomal dominant inheritance
1. Males and females are affected in equal proportions 2. Affected individuals are seem in multiple generations 3. Transmission by individuals of both sexes, to both sexes
42
Define penetrance
The percentage of individuals with a specific genotype showing the expected phenotype
43
Define expressivity
Refers to the range of phenotypes expressed by a specific genotype
44
In autosomal dominant inheritance what is the recurrence risk
50% for transmission of the mutation Dependant on penetrance and expression
45
Define anticipation
Genetic disorder affects successive generations earlier or more severely, usually due to expansion of unstable triplet repeat sequences
46
Define somatic mosaicism
Genetic fault present in only some tissues in the body
47
Define gonadal (germline) mosaicism
Genetic fault present in gonadal tissue
48
Define late-onset
Condition not manifest at birth (congenital), classically adult-onset
49
Define sex-limited
Condition inherited in the autosomal dominant pattern that seems to affect one sex more than another
50
Define predictive testing
Testing for a condition in a pre-symptomatic individual to predict their chance of developing a condition
51
What is the only mode of transmission where male to male transmission is seen?
Autosomal inheritance
52
Define x-linked inheritance
Genes carriers on the X chromosome
53
What are the three typical features of X-linked inheritance
1. Usually only male affected 2. Transmitted (usually) through unaffected females - Female carriers can be affected to lesser degree 3. No male-male transmission
54
Define lyonization (X inactivation)
Generally only one of two X chromosomes active in each female cell. Can be skewed
55
Can an infected male in X-linked inheritance have an affected son
An affected male cannot have an affected son But all daughters will be carriers
56
Define genomic imprinting
Epigenetic phenomenon that causes genes to be expressed in a parent-of-origin-specific manner
57
Define epigenetic
Non-genetic influence on gene expression
58
Define homoplasmy
A eukaryotic cell whose copies of mitochondrial DNA are all identical (identically normal or have identical mutations)
59
Define heteroplasmy
Multiple copies of mtDNA in each cell Can vary between cells in the same tissue or organ and organ to organ in the same person and between individuals of the same family
60
What are the 4 factors of mitochondrial genetic disease
Group of disorders caused by dysfunctional mitochondria Caused by mutations in the mitochondrial DNA (15%) Caused by mutations in nuclear genes, whose gene products are imported into the mitochondria Acquired conditions caused
61
What is the carrier frequency of sickle cell disease (haemochromatosis)
1/10
62
What is the carrier frequency of cystic fibrosis
1/25
63
Name some autosomal recessive conditions
Haemochromatosis (sickle cell disease) Cystic fibrosis Congenital adrenal hyperplasia Connexin-26 (deafness) Tay-Sachs disease MCAD disease Spinal muscular atrophy Friedreich's ataxia Hurler syndrome Ataxia telangiectasia
64
Describe cystic fibrosis
Commonest AR condition affecting northern European population Chronic condition mainly affecting lungs and guts - variable presentation Incidence - 1 in 2500 CFTR gene on 7q31.2 F508 commonest mutation (80%)
65
What is the sweat test
Diagnostic test for cystic fibrosis Not genetic marker
66
If someone in a parents genetic line has an autosomal condition what is the equation for risk to there child (if neither have been tested)
Parent with genetic line = 1/2 (chance a carrier) Parent b = 1/25 (population carrier frequency) Risk of affected child if both carriers = 1/4 1/2 x 1/25 x 1/4 = 1/200
67
Autosomal recessive One parent + one parent - equation
Chance parent a = 1 chance parent b = 1/250 (test only detects 90% mutations) risk of affected child if both carriers = 1/4 1/1000
68
What is the phenotype correlation in cystic fibrosis of genotype F508
Pancreatic insufficiency and chronic lung disease
69
What is the phenotype correlation in cystic fibrosis of genotype R117H
Majority are pancreatic sufficient but have chronic lung disease
70
What is an example of x-linked inheritance
Haemophilia
71
What is an example of multifactorial inheritance
Cleft lip and palate Combination of both genetic and environmental factors

IMMS (16 decks)

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