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BMS > Patterns of Single Gene Inheritance > Flashcards

Patterns of Single Gene Inheritance Flashcards

1
Q

What are the Mendelian patterns of inheritance?

A
  1. ) Autosomal Recessive
  2. ) Autosomal Dominant
  3. ) X-linked recessive
  4. ) X-linked dominant
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2
Q

What are the three exceptions of Mendelian patterns of inheritance?

A
  1. ) Reduced penetrance
  2. ) Variable Expressivity
  3. ) Sex-limited phenotypes
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3
Q

Determined primarily by an allele at a single chromosomal locus

-Caused by mutations that occur at a specific location on a locus

A

Single gene disorders

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4
Q

Single gene disorders are the result of a mutation at a specific locus on the chromosome. These mutations occur on a specific gene and result in a different

A

Phenotype

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5
Q

One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome

A

Allele

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6
Q

Set of alleles present at a single locus

-refers primarily to the autosomes

A

Genotype

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7
Q

Observable expression of the genotype

A

Phenotype

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8
Q

When the two alleles are the same (i.e. both WT or both mutant)

A

Homozygous

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9
Q

When one allele is WT and the other allele is a mutation

A

Heterozygous

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10
Q

When both alleles are mutant, but the mutation are at different locations in the gene

A

Compound heterozygotes

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11
Q

When an abnormal gene is located on an X chromosome in a male patient

A

Hemizygous

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12
Q

Distinct mutations in the same gene producing the same phenotype

A

Allelic Heterogeneity

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13
Q

Distinct mutations in the same gene producing very different phenotypes

A

Phenotypic heterogeneity

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14
Q

Descibes different mutations in the same gene that can sometimes give rise to strikingly different phenotypes

A

Phenotypic Heterogeneity

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15
Q

When mutations in more than one gene can cause the same disease

-Ex: Long QT syndrome can be cause by mutations to sodium channels, potassium channels, or structural proteins

A

Locus Heterogeneity

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16
Q

One gene that affects multiple traits

-Ex: Von Hippel-Lindau Syndrome

A

Pleiotropy

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17
Q

A single gene defect that affects multiple organs, produces multiple diverse phenotypes, and results in a variety of signs and symptoms

A

Pleiotropy

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18
Q

When multiple genes affect one trait

-Ex: Hair loss

A

Polygenic

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19
Q

Mutations at different loci that produce the same phenotype

A

Locus Heterogeneity

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20
Q

Affect 1:300 neonates and are responsible for 7% of pediatric hospitalizations

A

Single gene disorders

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21
Q

Most single gene disorders follow a pattern of

A

Mendelian Inheritance

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22
Q

Follow classic inheritance patterns and occurs in fixed and predictable proportions among offspring of specific types of matings

A

Mendelian Diseases

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23
Q

For Mendelian diseases, you can predict the pattern of inheritance and the genotype from the

A

Pedigree

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24
Q

Used to establish the pattern of transmission of single gene disorders

-Determined from the family history

A

Pedigrees

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25
Q

Can establish a pattern of inheritance and can be used to determine the degree of risk of disease for family members

A

Pedigrees

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26
Q

Early lethality of disorder, small family size, variable age of onset, and non-Mendelian inheritance can all

A

Confound pedigree interpretation

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27
Q

If the disease occurs early after birth, or during pregnancy,

A

Early lethality

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28
Q

The pattern of inheritance of single gene disorders is determined by what two factors?

A
  1. ) Whether phenotype is dominant or recessive

2. ) Chromosomal location of gene locus

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29
Q

Does not follow Mendelian inheritance

A

Mitochondrial Genome

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30
Q

Most of the time when we are talking about mutations in the sex chromosomes, we are talking about mutations on the

A

X-chromosome

Y mutations are very rare

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31
Q

An individual must have two mutant alleles and no wild type in order to have an

A

Autosomal Recessive (AR) Disease)

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32
Q

In an AR disease, the type of mutation in each allele CAN be different, i.e. you could be a

A

Compound Heterozygote

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33
Q

Reduce or eliminate function of the gene product

  • Often affect the function of enzymes
  • are RARE
A

AR Diseases

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34
Q

Cystic fibrosis is a common representative of an

A

AR disease

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35
Q

For an AR disease, the risk that a child will inherit the disorder is

A

25%

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36
Q

For an AR disease, the risk that a child will be a carrier is

A

50%

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37
Q

For an AR disease, the risk that a child will be an unaffected carrier is

A

2/3 (had to delete the affected)

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38
Q

In an AR pedigree, the parents are

A

Unaffected asymptomatic carriers

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39
Q

For an AR pedigree, what is the difference between number of affected males and females?

A

Affected males = # affected females

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40
Q

The more rare or unusual a trait is in a population, the more likely that the parents are

A

Related

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41
Q

Wilson’s disease is an example of an

A

AR disease

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42
Q

New mutations are VERY

A

Rare

Not typically the right answer choice

43
Q

What factors can affect the risk of inheritance for an AR disorder?

A
  1. ) Carrier frequency
  2. ) Consanguinity
  3. ) Inbreeding
  4. ) Genetic Isolates
44
Q

Increases the chance that both parents are carriers of the same mutant allele

-When second cousins or closer mate

A

Consanguinity

45
Q

When individuals from a small population choose mates from the same population

A

Inbreeding

46
Q

When certain races are more likely to develop a disease

-Ex: risk of Tay-sachs disease in Ashkenazi Jews (the carrier frequency is 10X higher than in other European populations)

A

Genetic Isolates

47
Q

Deposition of cholesterol in the tendons

A

Xanthoma

48
Q

Makes up more than 50% of known Mendelian disorders

  • Only one mutant allele is required for disease
  • Ex: Familial Hypercholesterolemia
A

Autosomal Dominant (AD) Disease

49
Q

The incidence of disorders can be high, especially in some populations, for

A

AD Diseases

50
Q

In general, BB homozygotes are exceedingly

A

Rare

51
Q

If an affected heterozygote (Bb) of an AD disease mates with an unaffected homozygote (bb), what is the chance that a child of either sex will be affected?

A

50%

52
Q

What is the risk that a phenotypically normal child has the mutant allele for an AD disease?

A

Zero (unless there is incomplete penetrance)

53
Q

Do not skip generations (i.e. ever affected individual has an affected parent)

A

AD Pedigrees

54
Q

For an AD pedigree, what is the difference between number of affected males and females?

A

Affected males = # affected females

55
Q

For an AD pedigree, male-to-male transmission does occur, and a male can have an unaffected

A

Daughter

56
Q

For an AD pedigree, unaffected individuals will have

A

Unaffected Children

57
Q

Most AD disorders display

A

Incomplete dominance

58
Q

Implies that an individual that is HOMOZYGOUS for the AD mutation will be more severely affected than an individual who is HETEROZYGOUS

A

Incomplete dominance

59
Q

What are two clinical examples of incomplete dominance?

A

Achondroplasia and Familial Hypercholesterolemia

60
Q

Means that all genotypes, homozygous or heterozygous, display the same phenotype

A

Complete Dominance

61
Q

What are two AD traits that create exceptions to the Mendelian Rules?

A

Reduced penetrance and Variable Expressivity

62
Q

When discussing the probability that a mutant gene will have ANY phenotypic expression at all. If the probability is less than 100%, then the gene has

A

Reduced penetrance

63
Q

A phenotype can have age dependent

A

Penetrance

64
Q

When all individuals with the disease ARE affected, but the severity (phenotype) of the disease differs in people who have the same genotype

A

Variable expressivity

65
Q

Penetrance is considered to be “all or none” in the sense that if 100% of the people have the phenotypic expression, then the gene has complete penetrance, but anything less than 100% is

A

Reduced (Incomplete) Penetrance

66
Q

An example of reduced penetrance is the AD form of split hand foot malformation, which has a reduced penetrance of

A

70%

67
Q

What is an example of a disease that has an age dependent penetrance and variable expressivity?

A

Neurofibromatosis

68
Q

Can make a pedigree difficult to interpret because the disease may appear to skip a generation

A

Reduced Penetrance

69
Q

Genes occur on the autosomes and the mutations are present in BOTH sexes, but the phenotype is evident only in one sex

A

Sex-linked autosomal traits

70
Q

The genes for the trait can be carried and transmitted by the opposite sex, although it is NOT displayed in that sex because of anatomical or physiological differences

A

Sex-linked autosomal traits

71
Q

What is the best characterized Sex-linked AD disorder?

A

Male-limited precocious puberty

72
Q

Mutation in lutenizing hormone receptor gene (LHR), which results in LHR being “on” all the time

-Only expressed in males

A

Male-limited precocious puberty

73
Q

Males affected with Male-limited precocious puberty develop secondary sexual characteristics w/ a growth spurt by the age of

A

4

74
Q

In a pedigree, male-to-male transmission (i.e. dad passes disease to son) excludes

A

X-linked disorder

75
Q

What is the most well documented sex-limited AR disorder?

-Most common single-gene inherited disease in the US

A

Hemochromatosis

76
Q

More common in males (5-10x) who have no physiologic process to reduce excess iron

-In women, pregnancy and menstruation reduce iron levels (10-20% incidence of males)

A

Hemochromatosis

77
Q

How many genes are there on the x-chromosome associated with disease phenotype?

A

300

78
Q

The dominant and recessive patterns of X-linked inheritance depends on the phenotype in

A

Heterozygous women

79
Q

You can have a female who is heterozygous for an X-linked disorder still display the phenotype because of

A

X-inactivation

80
Q

When discussing X-linked recessive (XLR) disorders, males are referred to as being

A

Hemizygous (XY)

81
Q

When a woman heterozygous for an XLR disorder mates with an unaffected male, what are the odds for the male and female children of being affected?

A
  1. ) 1:2 Risk that males will be affected

2. ) 1:2 risk that females will be carriers

82
Q

For an XLR, what are the odds if the male is affected but the female is unaffected?

A
  1. ) All females will be carriers

2. ) All males are normal

83
Q

What are the characteristics of an XLR pedigree?

A
  1. ) Males are affected more than females
  2. ) Heterozygous females are unaffected (depending on X-inactivation)
  3. ) Gene is transmitted from affected male to ALL daughters
84
Q

In an X-linked dominant (XLD) disorder, the trait is NEVER passe from the father to the

A

Son

85
Q

In an X-linked dominant (XLD) disorder, if an affected male and a normal female have kids, all the daughters are

A

Affected

86
Q

What is a characteristic of XLD disorders?

A

More females are affected than males

87
Q

Presence in an individual of at least two cell lines that differ genetically (due to a mutation) but are derived from a single zygote

-An exception to Mendelian inheritance

A

Mosaicism

88
Q

What are the two types of mosaicism?

A
  1. ) Pure somatic (occurs in somatic cells)

2. ) Pure germline (mutation occurs in germ cells)

89
Q

When parents who are phenotypically normal and who test negative for being a carrier have more than one child affected with a highly penetrant AD or XLR disorder, we suspect

A

Germline Mosaicism

90
Q

What are three examples of germline mosaicism?

A

Osteogenesis imperfecta, Hemophilia A and B, and Duschenne muscular distrophy

91
Q

Very rare in AR, but are a common cause of some diseases

  • probability is 10^-6 to 10^-7 per gamete
  • another cause for divergence from Mendelian inheritance
A

New Mutations

92
Q

Diseases that are produced by dominant alleles with effects so severe that persons with them do not have children (genetic lethal), are typically only observed when there are

A

New Mutations

93
Q

When looking at pedigree, if thing seem to REALLY not make sense, it is possible that there has been

A

Mis-attributed paternity

94
Q

Says that genes originating from maternal and paternal genomes are equally expressed in the offspring

A

Mendel’s Law

95
Q

What is a clear violation of Mendel’s law?

-Affects about 100 human genes located on select chromosomes

A

Genomic imprinting

96
Q

When the maternal allele is methylated and the methylated gene is NOT expressed

A

Maternal imprinting

97
Q

Nearly all mutations that create enzyme deficiency and matabolic disease are

-Because a single defective allele will only reduce function by 50%

A

Recessive

98
Q

What are the three major routes to dominance?

A
  1. ) Gain-of-function
  2. ) Haploinsufficiency
  3. ) Dominant-negative effect
99
Q

Mutation allows protein to function in ways not possible for the normal gene product.

Example: constitutive activity of ras, can be produced by amino acid substitutions that reduce GTPase activity, so that ras is always active, not just when growth factors bind receptors.

A

Gain-of-function

100
Q

When one functional allele cannot provide sufficient product for normal function.

Ex: 50% of normal protein C activity is not sufficient to prevent risk of thrombosis

A

Haploinsufficiency

101
Q

Created by nonsense, frameshift, or splicesite mutations that block production of any protein by the mutant allele

A

Haploinsufficiency

102
Q

If the active form of the protein is an oligomer, a single defective subunit can block function of the entire protein. This is an example of the

A

Dominant-negative effect

103
Q

The transcription factor p53 is a tetramer. Mutations that block DNA-binding by one of the four subunits can prevent function of the tetramer, leading to the

A

Dominant-negative effect

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