Autosomal inheritance Flashcards

1
Q

Define phenotype

A

observed properties (different levels such as physical or cellular phenotype) of an individual as determined by genotype and environment.

properties can be based on the genotype as well as the environment

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2
Q

Define autosomal dominant (AD), autosomal recessive(AR), and codominant phenotypes

A

AD=> phenotype present in the heterozygote

AR=>phenotype not apparent in the heterozygote

Codominant=>both alleles expressed in the heterozygote

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3
Q

Track segregation of alleles through a pedigree and be able to relate genotypes to phenotypes

A

AD=> -often seen in multiple generations of a family and affects both sexes and transmitted by either sex
-each offspring of an individual has a 50% chance to be affected

AR=>on avg, 2 carrier parents: 25% affected offspring, 25% homozygous normal offspring, 50% heterozygous carrier offspring

  • parents of an affected individual are obligate carriers and often normal
  • mutations are transmitted through many generations of heterozygous carriers and may be present in only one sibship
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4
Q

If a person has the genotype for sickle cell disease, but does not show the phenotype outwardly, how else will the phenotype be present?

A

-cellular level

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5
Q

When looking at the heterozygote (Aa), and there is no phenotype presence of the A then what type of trait is it?

A

-AR

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6
Q

If a patient has a genotype of aa but is normal phenotypically, what type of trait is it?

A

-AD

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7
Q

If a patient has an autosomal dominant genotype, how many dominant alleles must be present for the patient to have the disease?

A

-1 allele

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8
Q

Why do most autosomal dominant diseases rarely have 2 dominant alleles so you should assume the person is heterozygous for the condition (Aa)?

A

-most conditions the homozygous mutant is lethal

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9
Q

Which trait, AD or AR, has the most number of heterozygous non-affected carriers?

A

-AR

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10
Q

What could a loss of function mutation cause?

(Three things)

A

Loss of function mutations are common

  • terminates the protein (nonsense)
  • interfere with folding, unstable, degraded
  • protein produced but active site or confirmational change occurs then it is a loss of function
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11
Q

What is a gain of function mutation?

A

mutation causes protein to be expressed to lose control to cause over expression or expressed in the wrong tissues

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12
Q

What is a dominant negative mutation in collagen cause?

A

osteogenesis imperfecta due to collagen disruption

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13
Q

What is haploinsuffiency?

A

-half is not enough so if there is an autosomal dominant gene present then it will still cause the disease

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14
Q

Which trait, AD or AR, is characteristic of male-male transmission which helps distinguish the disorder from X-linked disorders?

A

AD

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15
Q

T/F Reduced penetrance and variable expressivity occur frequently in AD disorders

A

True

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16
Q

In an AR disease, what is the % of an unaffected sibling of an affected individual to be a carrier?

A

-67%

17
Q

Loss of function and clinical phenotypes:
At 50% of residual function, you have a correspondance to heterozygote with 1 normal and 1 nonfunctional allele, so with this information, describe what A, B, C, D will have with respect to the mutation at the given area.

A
  • A will be simple recessive with normal phenotype in heterozygote
  • B will be autosomal dominant; haploinsuffiency
  • C recessive with disease severity dependent of residual funciton
  • D recessive with varying organ involvement
18
Q

What percentage of genes are shared in a 1st degree relative?

A

-50% (1/2)

19
Q

What percentage of genes are shared in a 2nd degree relative?

A

-25% (1/4)

20
Q

What percentage of genes are shared in a 3rd degree relative?

A

-12.5% (1/8)

21
Q

The proportion of shared genes is reduced by what factor when there is one common ancestor rather than 2?

A

-50% or 1/2

22
Q

How many meiosis are 2 ppl separated from in 2nd degree relative?

A

2

23
Q

Half siblings share what percentage of their genes?

A

-25% or 1/4

24
Q

In an autosomal recessive trait, where there is 2 parent carriers (Dd), what is the recurrence risk to the fetus to have the trait?

A

-25% (1/4)= .5x.5

25
Q

In an autosomal recessive trait, where there is 2 parent carriers (Dd), their son is healthy and does not show the disease so what is the probability he is a carrier?

A

-67% (1/3)

26
Q

In the hardy-weinberg principle, there is a math relationship relating genotype freq. and allele freq., what are the 2 assumptions?

A
  • large population with random mating
  • genotype freq
27
Q

Hardy weinberg principle at a population level, what is the equation?

A
28
Q

Hardy weinberg principle at a population level, describe the punnet square.

A
29
Q

For a locus with 2 alleles where p=0.99. What is the % for a heterozygous offspring?

A

-2%

30
Q

The hardy-weinberg equation has a clinical relevance, what is it?

A

-estimate carrier frequencies and disease incidence in autosomal recessive diseases

31
Q

If the allele frequency for Tay-Sach’s mutations is 1/50, what is the incidence of affected children? What is the proportion of carriers in the population?

A

-q=1/50

-2pq=1/25

32
Q

A disease has an incidence of 1 in 40,000 in a population. What is the carrier frequency?

A

-q^2 = 1/40,000 so q is equal to 1/200

33
Q

For 3 possible alleles, what is the Hardy-Weinberg equation?

A
34
Q
  1. T/F For any heterozygote class in a population, genotype freq. = (2) x (allele 1 frequency) x (allele 2 frequency)
A

True