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MTM > Multifactorial Inheritance > Flashcards

Multifactorial Inheritance Flashcards

1
Q

Types of variation in genome (DNA variants - a continuum of effect)

A

Norma variation - eye colour
Difference in response to medication
Influence likelihood of disease
Directly result is genetic condition

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2
Q

How dna sequence variants affect health

A

Depends on location
Whether they alter essential genes

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3
Q

What is Mendelian inheritance

A

Caused by mutation in a single nuclear gene
Classical inheritance patterns
- dominant/ recessive
- autosomal/ X linked

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4
Q

What is non Mendelian inheritance

A

Polygenic (multiple genes)
Multi factorial
Maternal inheritance (mitochondrial)

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5
Q

What is multi factorial inheritance

A

Combination of changes in multiple genes and environmental factors

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6
Q

Types of Mendelian conditions

A

– Hypercholesterolaemia
– Marfan syndrome
– Cystic fibrosis
– Sickle cell disease
– Duchenne muscular dystrophy

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7
Q

Examples of multi factorial inherited conditions

A

More common:

– Coronaryarterydisease
– Diabetes mellitus
– Hypertension
– Cerebrovasculardisease
– Schizophrenia
– Breast and bowel cancers
– Some congenital anomalies

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8
Q

How is genetic component of Mendelian conditions highlighted

A

By pedigree pattern and recurrence risk

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9
Q

How is genetic component of multi factorial conditions highlighted

A

by clustering of cases in some families but no obvious inheritance pattern

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10
Q

Aetiology of diseases

A

Either 100% environmental
Single gene
Or polygenic

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11
Q

Features of Mendelian conditions

A

Rare
Genetics Simple
Unifactorial
High recurrence risk

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12
Q

Features of multi factorial inheritance

A

Common
Genetics complex Multifactorial
Low recurrence rate

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13
Q

How to identify genetic and environmental influences

A

observational studies of the incidence of diseases in different groups of people

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14
Q

Different ways evidence is gathered for observational studies

A

• Familial clustering
• Twin studies
• Adoption studies
• Population and Migration studies

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15
Q

What are monozygotic twins

A

Share all genetics and environment

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16
Q

What are dizygotic twins

A

Non identical
Share same amount of genetics as siblings
Share 50% genes and environment

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17
Q

How can you acquire evidence for genetic/ environmental influences

A

Comparing concordance of different features btw monozygotic and dizygotic twins

Determining the incidence of a disease in twins helps delineate whether there are genetic and environmental components

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18
Q

Through studying families where there was a multifactorial condition:

A

probabilities of recurrence for relatives were calculated for general use
by observing the numbers of relatives with the same condition in the studied families

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19
Q

What is polygenic inheritance

A

• Polygenic = many genes
• Large number of genetic factors, each making only a small additive contribution to the final phenotype

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20
Q

What are continuous traits

A

Typically, polygenic inheritance is the basis for continuous traits which follow a normal distribution in the population

displays a range of expression (such as weight, height, etc.) rather than an all-or-none appearance (such as white or red). Continuous traits are usually under polygenic control and subject to substantial environmental influence in expression.

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21
Q

How characters (like eye colour) are regulated

A

One pair of alleles at a single locus controlling a character
3 possible results
Blend of pair acts as 3rd possibility

22
Q

How many pairs of alleles needed to build a continuous distribution

A

Minimum three pairs

23
Q

What is a liability curve

A

Normal distribution - Made of genetic and environmental factors
Above threshold liability a person will develop the multifactorial disorder

24
Q

What is the probability of a relative having a multi factorial inheritance

A

The probability of a relative having a multifactorial disease is higher because they are more likely to share genes (and environment) in common and so increase their liability

25
Q

What kind of disease is spina bifida

A

Multifactorial inheritance

26
Q

What are bad about epilepsy drugs

A

Sodium balproate
Risk of developing spina bifida

27
Q

What do you notice
about the magnitude
of the recurrence risk in other family members for neural tube defects?

A

As you get further away from affected individual recurrence risk decreases because genetic makeup is less similar

28
Q

What is the empiric risk

A

The chance that a disease will occur in a family, based on experience with the diagnosis, past history, and medical records rather than theory

29
Q

What is the observed recurrence risk after one baby with NTD

A

4%

30
Q

Main points of multifactorial disorders

A

 Environmental influences act with a genetic predisposition
 Multiple genes with individually small risks often implicated
 One organ system affected

31
Q

What are recurrence risks

A
  • “empiric figures”
  • obtained from population studies

the likelihood that a hereditary trait or disorder present in one family member will occur again in other family members

32
Q

The threshold model of multifactorial inheritance

A

• The genes (diff genetic makeup) and environmental factors causing a particular multifactorial trait may vary from person to person

33
Q

What are other models ????

A

– major gene of large effect acting on multifactorial background
– small number of genes act together

34
Q

How did we begin to find genes for Mendelian disorders?

A

• Used families
• Identified by:
– A pedigree pattern indicative of a known mode of inheritance
– The diagnosis of a single gene disorder with a known mode of inheritance

35
Q

How are the genetic components of common conditions identified?

A

Genes for common disorders have to be identified through association studies in large populations.

36
Q

What do association studies rely on

A

The assumption that people with the same condition share a paticular DNA pattern

37
Q

What are SNPs

A

• SNPs are changes of a single base in a particular DNA sequence (in genes or non-coding sequences)
• The physical locations of SNPs are known
1/1000 nucleotide

38
Q

One method of identifying the genetic components of common complex conditions

A

• Through genome-wide association studies (GWAS)
• Thousands of people
• Test up to 500 000 SNPs in each person by microarray analysis

Comparing SNP frequencies of people with and without disease

39
Q

Example of how SNPs may affect susceptibility of disease

A

SNP in GWA affect susceptibility of diabetes
May be location of SNP rather than the SNP itself

40
Q
A

Most relative risks associated with particular SNP genotypes are usually low (x 1.1 – x 1.5)
- May increase or decrease risks
- May have variable effects in different combinations

 Therefore other genes and environmental factors involved.

41
Q

How can estimate of susceptibility of disease be given

A

In future clinical practice, SNPs associated with several genes maybe used together to give estimate of susceptibility – but complex +++!!

42
Q

What changes may be picked up using a SNP library

A

• May be direct effect
• May be indirect association / marker for nearby major
genetic influence

43
Q

Why is genomics informative for clinical practice

A

Genetic variants can alter drug response and cause adverse effects

New targeted therapies are being developed based on genomic information

Use info to specifically tailor patients drug management

Genomic info can influence health decisions, help people modify risk factors and provide motivation

44
Q

Types of potential feedback to participants of genomics

A

Mains findings: all patients receive results about main cond which they were referred for
Additional findings: an opt to receive feedback on selection of know genetic alterations of high clinical sig
Carrier status: parents who planning to have children can opt to find carrier status for genetic diseases

45
Q

Genomic England?

A

Government announced plans to sequence the full genomes of up to 100,000 NHS patients:
cancer
rare inherited diseases infectious diseases

46
Q

The impact of genetic testing on motivation to stop smoking:

A

Crohn’s disease used as an example
Population Sample (2008 study)
– Shown “their” genetic results
– Expressed motivation to quit
– More motivated if bigger risk

But still showed same behaviour with and without genetic test

47
Q

What is Crohn’s disease and symptoms

A

• Crohn’s Disease affects the gut.
• It tends to run in families, and is more common in smokers
• Symptoms include
– Abdominal pain
– Diarrhoea
– Fever
– Loss of appetite
– Weight loss
• The symptoms are so serious that some people with Crohn’s disease cannot work or go out.

48
Q

To personalise treatment and surveillance we can use genomic information to

A
  • sub classify their disease
  • access susceptibility
  • predict their response to drugs
  • choose best treatment
49
Q

Common complex disorders: key points

A

• Both genetic and environmental factors involved in many common conditions.
• Contributions of environment/genetics assessed through – effects of changing environment through migration or adoption
– observed incidence of disease in relatives
– concordance rates in twins
– evaluating association with genetic markers (SNPs) – Whole genome sequencing data / Clinical data
• Genetic factors: an inherited predisposition or due to a combination of genes conferring susceptibility
• To reduce probability that someone will develop a common disorder, need to identify individuals who are genetically susceptible and identify environmental agents involved

50
Q

What increases the chance of having dizygotic twins

A

Your chances of having Dizygotic twins are increased if you are over 35, take fertility drugs/ have IVF, are taller or overweight and if you have a family history of dizygotic twins on your mothers side (e.g. if you are a twin, your mother had other twins or your grandmother had twins) The chances are also increased 5 times if you have already had one set of dizygotic twins.
The chances for monozygotic twins are completely random

MTM (12 decks)

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