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Biochemistry > Bioc L02 and L03 Autosomal Dominant and Autosomal Recessive Inheritance > Flashcards

Bioc L02 and L03 Autosomal Dominant and Autosomal Recessive Inheritance Flashcards

1
Q

What is an autosomal trait?

A

the gene is localized to chromosome 1-22 (autosomes) rather than sex-linked or mitochondrial

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2
Q

What is a monogenic or Mendelian trait?

A

a trait produced by a single gene

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3
Q

What is a gene?

A

DNA sequence that codes for the amino acid sequence of one or more polypeptide chains. Specifies an inherited trait.

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4
Q

What is a locus?

A

The physical location of a particular gene in the chromosome.

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5
Q

What is an allele?

A

One or more alternative forms that a gene may have in a population. For one gene there can be many alleles in a population

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6
Q

What is Mendel’s Principle of Segregation? (First law)

A
  • Sexually reproducing organisms possess genes in pairs and only one each pair of each gene is transmitted to a particular offspring.
  • The genes remain intact and distinct in the next generation and in subsequent generations.
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7
Q

What is Mendel’s principle of independent assortment? (Second Law)

A

Genes that reside at different loci are transmitted independently. An allele that is transmitted at one locus has no influence on while allele is transmitted at another locus.

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8
Q

What is the principle of independece in relation to probability?

A

each event in probability is independent of every other

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9
Q

What is the multiplication rule, and what word should you look for?

A
  • in two independent trials the probability of obtaining a given outcome in both trails is the product of their independent probabilities.
  • What is the probability of having two girls? (one girl AND one girl)
  • prob of first girl x prob of second girl
  • 1/2 x 1/2 = 1/4
  • look for AND
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10
Q

What is the addition rule, and what word should you look for?

A
  • the probability of one outcome OR the other
  • add the probabilities together
  • What is the probability of having two girls OR two boys
  • prob of first event + prob of second event
  • 1/4 + 1/4 = 1/2
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11
Q

What is the gene frequency?

A
  • How often a particular gene sequence occurs in a population (T or t)
  • refers to either the normal or mutated gene
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12
Q

What is genotype frequency?

A
  • How often a given genotype occurs in a population.
  • 3 types of genotypes: TT, Tt, tt
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13
Q

What is the Hardy-Weinberg principle?

A
  • The frequency of the alleles in a population is mathematically related to the frequency of genotypes in a population.
  • It connects gene frequency with genotype frequency
  • (p + q)^2 = p^2 + 2pq + q^2 = 1
  • p is T
  • q is t
  • p^2 is TT
  • 2pq is Tt
  • q^2 is tt
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14
Q

What can we assume if we know that T and t are the only alleles?

A

p + q = 1

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15
Q

What are the three conditions with respect to the population that must be true in order to apply the H-W principle?

A
  1. Large population
  2. Random mating
  3. No mutations, migration, or natural selection
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16
Q

What are pedigrees based on?

A

observed phenotype

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17
Q

What is proband?

A

the first person in a pedigree to be identified clinically as having the disease in question.

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18
Q

What is an autosomal dominant disease?

A
  • requires only one disease allele for manifestation of the disease phenotype.
  • relatively rare in humans gene frequency of 0.1%
  • typically due to mutations in nonenzymatic structural proteins (collagen) or protein components of membranes or receoptors.
  • there is usually at least one affected individual in each generation.
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19
Q

What is Ehlers-Danlos Syndrome?

A

An autosomal dominant mutation in the gene that affects collagen. Overly stretchy skin

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20
Q

In autosomal dominant diseases, do two sexes exhibit the trait in equal proportions?

Is one sex more likely to transmit the trait to their offspring?

A

Yes, both sexes exhibit the trait in equal proportions.

No, both sexes are equally likely to transmit the trait to their offspring.

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21
Q

In autosomal dominant inheritance, affected individuals transmit the trait to about what percentage of their children?

A

50%

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22
Q

Does autosomal dominant inheritance have father to son transmission?

If there is father to son transmission, what does it exclude as the type of inheritance?

A

YES

If there is father to son transmission, it cannot be X-linked.

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23
Q

What does vertical transmission mean, and how does it apply to autosomal dominant inheritane?

A
  • no skipping of generations
  • there will be at least one affected individual in each generation
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24
Q

What is Huntington Disease and how is it inherited?

A
  • Autosomal dominant
  • HD gene: trinucleotide repeat expansion disease
  • symptoms: progressive dementia, choreic movements, late age of onset
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25
Q

What is occurence risk?

A

the risk of producing an affected child when no children have yet been produced.

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26
Q

What is recurrence risk?

A

the risk of producing an affected child when one or more children with the disease have been already produced

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27
Q

What is the occurrence and recurrence risk when one parent is affected by an autosomal dominant diseasea and the other is not?

A

Both occurence and recurrence risk is 50%.

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28
Q

What is Achondroplasia?

A
  • autosomal dominant
  • point mutation in FGFR-3 gene, resulting in glycine to arginine missense mutation
  • gain of function
  • Symptoms: short limbed dwarfism, characteristic faces, radiological features of spine
  • 1/10,000
29
Q

Homozygotes are much more severely affected in all dominant diseases EXCEPT:

A

Huntington disease

30
Q

What percentage of Achondroplasia patients are the result of a new mutation in the gene?

A

90%

31
Q

What is Neurofibromatosis Type I?

A
  • autosomal dominant
  • affects NF1 gene
  • Symptoms: cafe-au-lait spots, fibromatous skin tumors, increased risk of malignancy in tumors
  • 1/3,000 to 1/5,000
32
Q

What are the two ways that Neurofibromatosis Type I can complicate pedigree analysis?

A
  1. 50% of patients are the result of a new mutation in the gene
  2. There is a high degree of variability in the symptoms.
33
Q

What is Marfan syndrome?

A
  • autosomal dominant
  • FBN1 gene (fibrillin)
  • Symptoms: Disproportionate tall stature, arachnodactyly, skeletal abnormalities, cardiovascular problems
34
Q

What is the incidence of Marfan syndrome, and what percentage of patients are a result of a new mutation in the gene?

A
  • Incidence: 1/5,000 to 1/10,000
  • 25% patients result of new mutation
35
Q

What is Familial Hypercholesterolemia?

A
  • autosomal dominant
  • LDL receptor gene
  • loss of function
  • Symptoms:
    • Heterozygous- elevated LDL is plasma (300-400 mg/dL) leading to deposition of cholesterol in tendons, skin, arteries
    • Homozygous-much earlier and more extreme. Plasma cholesterol from 600-1,200 mg/dL
  • Death due to MI is common during childhood
36
Q

What is autosomal recessive inheritance?

A
  • requires both alleles to manifest a disease phenotype
  • parents of affected children will usually both be heterozygous carriers, meaning 1/4 of their offspring will manifest the disease
37
Q

Most autosomal disease to date have been mutations in genes that encode what?

A

enzymes

38
Q

Most genetic defects in metabolism are inherited in what fashion?

A

autosomal recessive

39
Q

What are four characteristics of autosomal recessive inheritance?

A
  1. Disease seen in one or more siblings, but not in earlier generations. Usually no prior family history
  2. Males and females are equally affected
  3. On average, 1/4 of the offspring of matings between two heterozygous carriers will be affected.
  4. Consanguinity is present more often in these pedigrees.
40
Q

What is Hurler syndrome?

A
  • autosomal recessive lysosomal storage disease
  • affects alpha-L-iduronidase gene, which produces and enzyme that catalyzes the breakdown of glycosaminoglycans
  • deficiency results in buildup of glycosaminoglycan in lysosomes
  • Symptoms: skeletal abnormalities, short stature, metnal retardation, corneal clouding, course of facial features.
41
Q

What is Hereditary Hemochromatosis?

A
  • autosomal recessive
  • mutation in HGE gene that results in iron overload
  • homozygotes absorb 2-4 times the normal amount of iron through intestine
  • extra iron accumulates in liver, heart, panceas, skin, joints, endocrine glands
42
Q

How can Hereditary Hemochromatosis be treated?

A

bloodletting

43
Q

What is the most common cause of death among untreated severely affected patients with Hereditary Hemochromatosis?

A

cardiac failure

44
Q

Although Hereditary Hemochromatosis is not sex-linked, what is one possible reason why adult males are more commonly affected?

A

Female homozygotes may lose extra iron during menstruation.

45
Q

What are 10 complications to patterns of inheritance?

A
  1. new mutation
  2. germline mosaicism
  3. delayed age of onset
  4. reduced penetrance
  5. variable expression
  6. pleiotropy
  7. heterogeneity
  8. genomic imprinting
  9. anticipation
  10. cosanguinity
46
Q

What are new mutations?

A
  • newborn with a dominant genetic disease when there is no history of the disease in the family.
  • could be the result of a novel, dominant acting mutation in the germ cell in one of the parents
47
Q

What is the recurrence risk in other siblings of a new mutation?

A

low

48
Q

What is the occurenc risk for affected children’s (by new mutation) offspring?

A

50%

49
Q

What are some examples of new mutation diseases?

A
  • achondroplasia (90%)
  • NF1 (50%)
  • Marfan (25%)
50
Q

What is germline mosaicism?

A
  • consists of more that one distinct population of cells (normal and mutated)
  • during development of parent, mutation occured that affected all or some of the germ cells, but not enough of the somatic tissue to produce a phenotype
  • rare
51
Q

When should germline mosaicism be considered?

A

When two or more offspring present with an autosomal dominant disease with no prior family history.

52
Q

What is an example of germline mosaicism?

A

osteogenesis imperfecti

53
Q

The recurrence risk in achondroplasia is higher or lower than the recurrence risk in osteogenesis imperfecti?

A

lower, because achondroplasia is a result of a new mutation that happens in germ cells during development of the child, and does not come from the parents On the other hand, OI is a result of a germline mutation occurs during development in the parent and gets passed on to the child.

54
Q

What is delayed age of onset?

A
  • genetic disease that does not manifest until adulthood.
  • individuals are unaware of their disease until after they have had children and possibly passed on the gene
  • symptoms usually not seen until 30 years of age or later
  • reduces natural selection against disease gene
55
Q

What are two examples of delayed age of onset?

A

Huntingtom disease and hemochromatosis

56
Q

What is reduced penetrance?

A
  • penetrance indicates the proportion of individuals carrying a particular genotype that also express the associated phenotype
57
Q

What is an example of reduced penetrance?

What is the penetrance of this disease?

A

Retinoblastoma

  • Incidence: 1/20,000
  • Penetrance= 90%, meaning that 90% of the individuals with the mutant genotype will develop the disease, but 10% will not
  • This 10% can still transmit the disease to later generations.
58
Q

What is variable expression?

A
  • concerns severity of the disease
  • independent of penetrance
  • causes are unknown
59
Q

What is an example of a disease that has variable expresion?

A

NF1

A parent with mild NF1 can transmitthe gene to a child who can then have a much more severe symptom.

NF1 is 100% penetrant with variable expression.

60
Q

What is pleiotropy?

A

A pleiotropic gene is one that exerts its effects on multiple aspects of physiology or anatomy

Ex: Cystic fibrosis, Marfan syndrome, von Gierke disease, diabetes

61
Q

What is heterogeneity?

A

where mutations at different gene loci can produce the same phenotype

Ex: Osteogeneis imperfecti can result from mutations in col1A1 on chromosome 17 or on the col1A2 gene on chromosome 7. The product of both genes is necessary for the formation of the functional type 1 collagen triple helical protein.

62
Q

What is Genomic Imprinting?

A
  • deletion of genetic material on the long arm of chromosome 15. If deletion is inherited from father offspring manifest Prader-Willi syndrom. If deletion is inherited from the mother, offsping manifest Angelman syndrome.
  • alters the expression of genes such that paternal and maternal chromosomes contribute different amounts of a gene product.
63
Q

What is anticipation?

A
  • a genetic disease that displays an earlier age of onset and or more severe expression in more recent generations of a pedigree.
  • myotopic dystrophy, Fragile X syndrome, Huntington disease
64
Q

What is Myotonic dystrophy?

A
  • a progressive muscle deterioration disease that affects 1/8,000.
  • by analysis of the gene DMPK, myotonic dystrophy is cause by and expansion of a trinucleotide (CTG) in the 3’ untranslated region of the gene
  • the number of repeats correlates with how bad the symptoms are
  • 5-50 repeats: no symptoms
  • 50-100: mild
  • 100-1,000: full myotonic dystrophy
65
Q

How is myotonic dystrophy a disease of anticipation?

A

the number of repeats often increases in succeeding generations due do a slippage of DNA polymerase during replication.

66
Q

What is cosanguinity?

A
  • mating between related individuals
  • more likely to produce offspring affected by autosomal recessive disorders, because relatives often share disease genes inherited from a common ancestor.
  • must be suspected when very rare recessive diseases are seen in a family
67
Q

What is our genetic burden?

A
  • that each person carries five recessive genes in heterozygous form that would result in a lethal phenotype if they were present in a homozygous state.
  • it has been shown that matings between related individuals produce a high frequency of mortality.
68
Q

What are some examples of autosomal dominant diseases?

A
  • Huntingtom disease
  • Achondroplasia
  • NF1
  • Marfan Syndrome
  • Familial Hyercholesterolemia
69
Q

What are some examples of autosomal recessive diseases?

A
  • Hurler syndrome
  • Hereditary hemochromatosis
  • Cystic fibrosis
  • Sickle-cell anemia
  • Phenylketonuria (PKU)
  • beta-thalassemia
  • Tay-Sachs

Biochemistry (10 decks)

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