Multifactorial Inheritance Flashcards

1
Q

What are the classic single gene disorders?

A

Sickle cell
cystic Fibrosis
duchenne dystrophy

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2
Q

what is a characteristic of Multifactorial traits?

A
  • Trait does not demonstrate a simple mendelian pattern
  • Familial aggregation
  • More common among the close relatives of the proband and less common in relatives who are less closely related
  • Environment also interacts with genotype to produce the final phenotype
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3
Q

What is the model that tries to explain multifactorial traits?

A

Liability/threshold

attempts to describe a populations genetic and environmental susceptibility.

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4
Q

What is liability?

A

all factors that contribute to the disease

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5
Q

What is threshold?

A

The limit to which normal is defined.
Passing threshold will make them affected

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6
Q

Liability in multifactorial diseases

A

Disease state is determined by both genes and environment

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7
Q

What is this image of?

A

Liability model and familial aggregation

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8
Q

What happens when there are bad genes in the liability and threshold model?

A

The curve is moved to the right- more of the population is above the threshold point

The threshold line moves to the left-in essence the same thing as more of the population is under the affected portion of the curve

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9
Q

Relative Risk ratio

A

Prevalence of disease in relatives of affected person / prevelance of disease in general population

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10
Q

What does the liability threshold model explain?

A

Explains the pattern of recurrence risk in families

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11
Q

What is Pyloric stenosis? What does it mean is a female has it in regards to recurrence risk?

A

Hypertrophy of the muscle between the stomach and intenstines,causing it to narrow(stenosis) impeding gastric emptying.

More common in male babies

If a female child gets it, that means there is a higher reccurence risk f because the parents have more of the bad gene

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12
Q

Symptoms of pyloric stenosis

A

Severe vomiting

palpation of the abdomen may reveal a mass in the epigastrium

may cause other problems such as dehydration and salt fluid imbalances

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13
Q

What are tools for determing the effects of genetic versus environment?

A
  • Population/migration studies
  • Family studies
  • twin studies
  • adoption studies
  • Association studies
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14
Q

Population/Migration studies

A

Indicative of environmental factors.

Disease incidences differences between populations suggest a genetic basis for that disease.

Could be due to cultural/lifestyle differences.

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15
Q

It is known that Asian women have a lower incidence of breast cancer than American women. The Asian women move to America and within two generations, their incidence increased to near american levels. What experiment/study is this an example of?

A

Population/Migration study.

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16
Q

What is concordance?

A

Both twins have the same disease

17
Q

What is Discordance?

A

One twin has the disease, the other twin does not.

18
Q

Monozygotic Twin (M.Z)

A

Derived from a single ovum

Genetically identical

19
Q

Dizygotic Twins (D.Z)

A

Derived from two seperate ova but share intrauterine environment.

Have genome similar to being regular siblings.

20
Q

What is the relationship of concordance between M.Z and D.Z?

A

The greater the difference in concordance rate between M.Z and D.Z twins= greater genetic input.

21
Q

What are limitations to twin studies?

A
  • May underestimate heritability
  • M.Z do have SOME different genes(like mitochondrial genes) and epigenetic differences
    • also different accumulation of somatic mutations due to errors in mitosis
  • Different environmental exposures
  • Different genes in different twin pairs
    • Studies between different sets of twins may point to different contributors for same phenotype
  • Ascertainment pairs
  • Most studies do NOT specify the loci and alleles but how genotype and environment interact
22
Q

What is the purpose of Association Analysis?

A

To test the co-occurence of a specific allele at a marker locus and a trait in a population by comparing the frequency of an allele in patients and controls

23
Q

What is Genome Wide Association studies?

A

Compares the genome of people with an illness to unaffected people to identify associations between SNPs and phenotype.

24
Q

What are two types of neural tube defects?

A

Anencephaly and Spina Bifida

25
Q

Anencephaly

A

Under developed brain and incomplete skull

May have brain stem function

most do not survive more than a few hours after a birth

26
Q

Spina bifida

A

Incomplete closure of the spine

Repair may be done in utero or postnatally

can be variable in severity

27
Q

Spina Bifida and incidence rates

A

Incidence = (1 to 2) / 1000

28
Q

Spina Bifida: Evidence for genetics

A

A woman who has had one child with a neural tube defect such as spina bifida has ~3% risk of having another

Mutations in genes coding enzymes for folate metabolism

29
Q

Spina Bifida

A
  • Supplementation of the mother’s diet with folate can reduce the incidence of neural tube defects by about 70%
    • The 3% risk of the woman having another child with a NTD can be reduced to 1% with high doses of folic acid