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Genomics > Non Mendelian Inheritance > Flashcards

Non Mendelian Inheritance Flashcards

1
Q

Definition of phenocopies/genetic heterogeneity

A

Many different alleles/gene variants => 1 phenotype

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2
Q

Definition of incomplete penetrance

A

Have the genotype associated with the disease but disease phenotype is not expressed

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3
Q

Definition of sib pair analysis

A

The idea that if a marker is linked to a disease locus, the same marker allele will be inherited by 2 siblings who express disease more often than expected by chance

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4
Q

Definition of syntetic

A

Whether the genes are on the same chromosome

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5
Q

What is the mode of inheritance for mitochondrial diseases

Is male to female transmission possible? Why?

A

Matrillineal inheritance
Female => both genders equally
Male => female transmission is not possible

Egg cell contains nuclear DNA and mitochondria
Sperm contains nuclear DNA and mitochondria but only nuclear DNA is passed on

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6
Q

What are the 3 factors that contribute to the expression of a mitochondrial disease

A

Type of mutation

Amount of abnormal vs normal mitochondria

  • heteroplasmy, mix of normal and mutant mitochondria in each cell
  • homoplasmy, mitochondria in a cell are all the same

Organ system affected

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7
Q

What is genomic imprinting
What sort of imprinting is considered normal

What are the 2 outcomes if imprinting goes wrong

A

Certain genes expressed in a parent of origin specific manner
If allele inherited from 1 parent is imprinted => silenced so only maternal allele expressed

Normally, we have 1 active copy of an imprinted gene
-improper imprinting leads to either
2 active copies 2 inactive copes

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8
Q

Describe what has gone wrong in Prader Willi and Angelman Syndrome

A

Prader Willi

  • deletion/mutation in paternal genes
  • no active copies of affected genes

Angelman Syndrom

  • deletion/mutation in maternal genes
  • no active copies of affected genes
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9
Q

Describe what is multifactorial/complex inheritance

A

Phenotypes that don’t express classic Mendelian inheritance
-single genes cannot explain phenotypic variation

Genes and environment influence traits

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10
Q

What are the 2 main types of complex traits
Describe them

What are the properties of complex inheritance

A

Polygenic

  • +1 genes with small additive effects
  • pure polygenic traits are v rare

Multifactorial

  • +1 genes and environment
  • no Mendelian ratios

Common polymorphisms associated with complex disease have small additive effects
If additive effect is large enough => disease

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11
Q

What is familial aggregation

What can also account for the increased prevalence of a complex disease in families

A

Families share a larger proportion of their alleles than the general population => higher prevalence of disease with complex inheritance

Non genetic factors may also lead to the expression of the disease as families often share similar environmental exposures

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12
Q

What is concordance and what are the 2 causes of disease concordance

A

2 individuals both express the disease

Due to

  • similar/same alleles
  • genetic heterogeneity/phenocopies
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13
Q

What is discordance and what are the 2 causes of disease discordance

A

Individuals in a family do not all express the disease

Due to

  • different alleles found in each individual
  • incomplete penetrance
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14
Q

Why is it hard to identify genes/causes of polygenic/multifactorial diseases

Describe the relative concordances of disease in MZ and DZ with monogenic and complex diseases

A

Incomplete penetrance and phenocopies

MZ have higher concordance in monogenic diseases
Both MZ and DZ have lower concordance for complex diseases

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15
Q

How would you estimate the risk of a disease recurring in a family
What factors lead to a higher risk

A

Empiric risk

  • based on observations within a family
  • used to predict recurrence of a trait in a family

Higher risk associated with

  • increased severity
  • no of affected relatives
  • sex
  • relatedness to affected individuals

Heritability

  • estimates proportion of variation in a population for a multifactorial trait due to genotype
  • coefficient of relatedness => proportion of genes relatives share
  • higher COR as more closely related people compared
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16
Q

How would you map the genetic cause of a condition

A 
Linkage analysis
Association studies/case controls
GWAS
NGS
Detecting large structural variations
New approaches to understanding the aetiology of complex diseases on a molecular level
17
Q

Why would you use linkage analysis to map the genetic causes of a condition
What is the threshold value

A

Used to identify a region of the genome that contains the causative gene

cM (unit of measure)
The larger the marker, the further they are from each other

Greater than 50 => unlinked

18
Q

How would you use the affected pedigree method (sib pair analysis) to map the genetic causes of a condition

A

Linkage analysis of complex polygenic conditions that relies on pairs of family members who are concordant for a trait

-sibling-sibling or parents-sibling pairs used as they share DNA from a direct inherited lineage

19
Q

How would you use case control studies to map the genetic cause of a condition

A

See if the trait expressed is associated with a particular genotype

Compare with controls who don’t express the trait

20
Q

How would you use linkage disequilibrium to map the genetic cause of a condition

A

See if the presence of a mutated/pathogenic allele is associated with another allele at a specific locus

21
Q

How would you use GWAS to map the genetic cause of a condition
How much data would you need
What is the downfall of findings in GWAS

A

Identify large no’s of common variants associated with disease in an assay

Data obtained from many samples to provide statistical confidence needed for disease association

However, associated variants may not directly cause disease
-linkage disequilbrium is possible => more steps needed to identify variant

22
Q

How would you use NGS to map the genetic cause of a condition
What is the downfall of NGS

A

By sequencing genomes/exomes, can find causative variants in rare/complex diseases, including detection of potential de novo mutations

NGS effective for common variant identification
-loci selection needed for SNP arrays can limit detection of rare variants occurring at a low frequency in a population

23
Q

Why would you detect large structural variation to map the genetic cause of a condition

A

Copy no variants result in abnormal no’s of gene copies

  • duplication
  • deletions
  • inversions

Can predispose to common complex conditions

Genomics (17 decks)

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