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Biochem BLOCK 4 > Single Gene Disorders And Population Genetics > Flashcards

Single Gene Disorders And Population Genetics Flashcards

1
Q

What are the two general types of autosomal dominant disorders?

A
  1. Loss of function

2. Gain of function

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2
Q

What are some causes of loss of function mutations?

A
  • Defects in structural proteins (collagen mutations in OI)

- defects in regulatory proteins (LDL receptor deficiency)

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3
Q

Gain of function mutations

A

Gain of function mutations endow normal proteins with toxic properties (Huntington’s)

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4
Q

What type of disorder is neurofibromatosis type 1?

A

Autosomal dominant

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5
Q

What is the gene defect for neurofibromatosis type 1?

A

Mutation in a cell cycle regulatory proteins

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6
Q

What is the incident of neurofibromatosis type 1?

A

1 in 3000

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7
Q

An important genetic concept that is epitomized by NF type 1 is:

A

Variable expression, even within the same family.

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8
Q

What is a hallmark of neurofibromatosis type 1?

A

Variable expression

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9
Q

What remains constant in neurofibromatosis type 1?, what is the clinical diagnostic clue?

A

Lisch Nodules

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10
Q

What type of disorder is Marfan Syndrome?

A

Autosomal dominant

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11
Q

What is the gene defect of Marfan Syndrome?

A

A mutation in the fibrillin gene

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12
Q

Marfan syndrome is a good example of a genetic principle called:

A

Pleiotropy

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13
Q

When a single mutation affects multiple organ systems a common feature of many genetic diseases

A

Pleiotropy

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14
Q

What are ocular abnormalities of Marfan Syndrome?

A

Myopia and detached lens

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15
Q

What type of disorder is thalassemias?

A

Autosomal recessive

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16
Q

What is the genetic defect of thalassemias

A

Imbalance in globin chain synthesis

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17
Q

Where is thalassemias most prevalent?

A

Mediterranean sea, parts of africa, and southeast asia

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18
Q

What are the two types of thalassemia

A
  • alpha thalassemia

- beta thalassemia

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19
Q

Results from insufficient synthesis of the alpha chain (B chain accumulates)

A

Alpha thalassemia

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20
Q

Results from insufficient synthesis of the B-chain (A chain accumulates)

A

B-thalassemia

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21
Q

Which type of thalassemia is more detrimental

A

B-thalassemia

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22
Q

What benefit is there to having thalassemias?

A

Malaria resistance

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23
Q

What does thalassemias cause?

A

Premature death of cells destined to become red blood cells-results in hemolytic anemia

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24
Q

Males are said to be _____ for genes on the X chromosome

A

Hemizygous

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25
Q

Males need how many copies of a defective X-linked genes to show symptoms?

A

One

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26
Q

Phenotype issues from X-linked recessive are much more common in which sex?

A

Males

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27
Q

What causes hemophilia A and B?

A

Absence of blood clotting factors

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28
Q

What are the mutation types for hemophilia A and B

A

Deletions, nonsense, mutations, DNA inversions

Severity related to mutation type

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29
Q

What is the firs thing you notice in hemophilia

A

Prolonged bleeding episodes, may be first noticed at birth with prolonged bleeding from the cord or umbilical area, or circumcision

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30
Q

What are some common features of hemophilia

A
  • prolonged bleeding episodes
  • intracranial hemorrhage
  • easy bruising
  • hemarthosis
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31
Q

Why is AIDS the most common cause of death for patients with hemophilia

A

They are treated with blood transfusions that has not had the viruses killed, sometimes AIDS is present. They don’t kill the viruses in the blood because it disrupts clotting factors

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32
Q

What is another term for X inactivation

A

Lyonization

33
Q

X inactivation

A
  • genes on on X chromosome are unavailable for transcription
  • inactive X chromosome can be observed by EM as a highly condensed Barr Body in the nuclei of interphase cells
  • associated with highly methylated DNA
34
Q

X inactivation being incomplete

A

Some genes on the activated chromosome remain available for transcription

35
Q

What is the explanation why some female hyterozygotes with one mutant X chromosome can show symptoms of an X-linked recessive disease

A

X inactivation

36
Q

Rare cases of single gene disorders that do not manifest until later in life

A

Delayed age onset

37
Q

What are examples of delayed age onset diseases

A

Huntington disease
-30-40 age of onset in first generation

Myotonic dystrophy
-30-40 in first generation

38
Q

When the same disease phenotype can be causes by mutation in different loci (in different genes)

A

Locus heterogeneity

39
Q

Example of locus heterogeneity

A

EDS (ehlers-danlos syndrome)

40
Q

What inheritance patterns can EDS display?

A

Autosomal dominant, autosomal recessive, X linked

41
Q

What are the characteristics of EDS autosomal dominant

A

Mutations in collagen genes

42
Q

What are the characteristics of EDS autosomal recessive?

A

Mutations in the lysyl hydroxylase

43
Q

What are the characteristics of EDS x linked (recessive)

A

Mutation in a copper-binding proteins (gene located on the X chromosome) leads to reduced copper availability in the serum; shopper is essential for the activity of lysyl oxidase (cross linking of collagen fibers)

44
Q

All genetic disease begin with a _________

A

New mutation

45
Q

In cases with a high mortality or low fertility rate, it is often due to a _______

A

New mutation

46
Q

This is particularly true with the autosomal dominant diseases and X linked recessive diseases, where the phenotype would be seen immediately (AD) or very soon (X-linked) in the pedigree

A

New mutation

Immediately shows up in pedigree and are detrimental and hard to pass on, gets weeded out

47
Q

___________ refers to diseases where the most recent generations of affected individuals show an earlier onset and more severe symptoms than previous generations

A

Anticipation

48
Q

Anticipation refers to diseases where the most recent generations of affected individuals show:

A
  • an earlier onset

- more severe symptoms than previous generations

49
Q

The effect of anticipation is most often associated with diseases cause by _____________

A

Trinucleotide repeat expansions

50
Q

What are some examples of anticipation

A

Fragile X syndrome, myotonic dystrophy, and huntingtons disease

51
Q

The severity of the disease and the age of onset are correlated directly with what?

A

The length (number of repeated) of the segment containing repeats )the size of the expansion)

52
Q

What will eventually happen with anticipation in later generations?

A

Although considered an adult disease, in later generations symptoms may first appear in childhood, due to expansion of the trinucleotide repeat

53
Q

Assumptions for Hardy Weignberg

A
  • large population
  • random mating with respect to they genotype at a given locus
  • constant and predictable relationship between genotype freq and gene freq
54
Q

This allows us to use simple math to determine the genotype frequencies if we know gene frequencies (and vice versa)

A

Hardy Weinberg

55
Q

What do you use to find gene frequency?

A

Hardy weinberg

56
Q

What part of hardy weinberg do you use for gene freq?

A

p + q=1

57
Q

How do you use hardy weinberg to find genotype freq

A 
Allele 1 = p
Allele 2= q
Freq of genotype 1/1 (pp): p^2
Freq of genotype 1/2 (pq): 2pq
Freq of genotype 2/2 (qq): q^2

P^2+2pq+q^2=1

58
Q

Hardy weinberg can estimate the carrier frequency of a rare disease of _____________ inheritance only

A

Autosomal recessive

59
Q

Example of hard weinberg carrier frequency in PKU with prevalence of 1 in 10,000

A

PKU is qq (recessive)= q^2=1/10,000

Q=square root (1/10,000)=1/100=0.01

P=1-q
P=1-0.01=0.99

Gene freq are q=0.01 and p=0.99

pp=0.99^2=0.98
Pq=2pq=2(0.01)(0.99)=0.02 or 1/50

The number of carriers for PKU is about 1 in 50

60
Q

Quicker way of finding number of carriers in hardy weinberg with cystic fibrosis incidence of 1 in 25,000

A

Q=square root of (1/2500)=1/50=0.20

0.02x2=0.04 or 1/25

61
Q

Ulprimary source of all new genetic variation in populations

A

Mutation

62
Q

Do mutation rates differe very much from population to population?

A

No

63
Q

Influences gene frequencies by selecting for genes that promote survival or fertility (referred to as fitness)

A

Natural selection

64
Q

Exposed to gene selection more often, generally have lower gene frequencies than recessive disease genes that can remain hidden in heterozygotes

A

Dominant disease genes

65
Q

Do all recessive genes has low rates?

A

No, some have a very high rate

  • sickle cell anemia- 1in 50 births in africa
  • carrier rate about 1 in 3.5
66
Q

Why is the carrier rate so high for sickle cell anemia in Africa

A

Gives fitness to individual who live in area high in malaria

67
Q

Natural selection has a _______ advantage

A

Heterozygote

68
Q

Heterozygotes for the sickle cell mutation (carriers)

A

The plasmodium survives very poorly and those people generally escape the worst infection with malaria

69
Q

Heterozygotes for thalassemia mutations

A

Have some protection against malaria

70
Q

Heterozygotes for the cystic fibrosis mutation

A

Protected against typhoid fever

71
Q

Genetic drift

A
  • occurs in populations with finite (Small) population size
  • can be particularly rapid in very small populations
  • also called founder affect
72
Q

Relatively rare alleles are Preston in higher abundance in a small, isolated population that goes on to colonize the area

A

Founder affect

73
Q

Example of founder affect

A

More cases of ellis van creveld disease (very rare autosomal recessive disease) are seen in old order amish than the rest of the world

74
Q

What type of disorder is ellis van creveld disease

A

Very rare autosomal recessive disease

75
Q

Symptoms of ellis van creveld

A
  • polydactyl

- shirt limbed dwarfism

76
Q

What is ellis van creveld disease caused by?

A

Caused by defective EVC gene, unknown function

77
Q

__________ results in the exchange of genes among populations

A

Gene flow

78
Q

________ is being seen more frequently as many parts of the world become less isolated and breeding between different populations becomes more commonplace

A

Gene flow

Biochem BLOCK 4 (11 decks)

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