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BMS2.01 Single Gene Inheritance (CORBETT) > Patterns of Single Gene Inheritance > Flashcards

Patterns of Single Gene Inheritance Flashcards

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1
Q

Locus definition:

A
  • physical site or location of a specific gene on a chromosome
  • two alleles for each locus (one each on each parental chromosome)
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2
Q

Genotype definition:

A
  • set of alleles present at a single locus
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3
Q

Phenotype definition:

A
  • observable expression of the genotype
  • Can be:
    • biochemical
    • cellular
    • physical (clinical)
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4
Q

Single gene disorders are:

A
  • diseases caused by mutations in a single gene.
    • significant disease burden on society, especially in neonates and pediatrics
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5
Q

Homozygous definition:

A
  • both alleles are the same
    • i.e. both wild type or both mutant
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6
Q

Heterozygous definition:

A
  • one allele is wild type
  • one allele is mutant
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7
Q

Compound heterozygous definition:

A
  • both alleles are mutant, but mutations on each chromosome are at different parts of the gene
    • ex: cystic fibrosis
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8
Q

Hemizygous:

A
  • abnormal gene is located on chromosome X
    • note: male patients only have a single X chromosome (XY)
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9
Q

Allelic heterogeneity definition:

A
  • DIFFERENT MUTATIONS IN THE SAME GENE result in the SAME clinical phenotype
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10
Q

Phenotypic heterogeneity definition:

A
  • DIFFERENT MUTATIONS IN THE SAME GENE result in VERY DIFFERENT clinical phenotypes
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11
Q

Locus heterogeneity definition:

A
  • MUTATIONS IN DIFFERENT GENES (at distinct loci) CAN result in the SAME CLINICAL PHENOTYPE
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12
Q

Mendelian diseases:

A
  • follow one of four classic inheritance patterns
  • occur in fixed and predictable proportions in offspring
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13
Q

Pedigrees are used to:

A
  1. establish the pattern of inheritance of single gene disorders
  2. determine degree of risk of disease in offspring

determined by family history

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14
Q

Four factors that can confound pedigree interpretation:

A
  1. early lethality of disorder
  2. small family size
  3. variable age of onset; decreased penetrance or variable expressivity
  4. non-Mendelian inheritance
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15
Q

Male pedigree symbol:

A

square

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16
Q

Female pedigree symbol:

A

circle

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17
Q

The two factors that determine pattern of inheritance of single gene disorders:

A
  1. whether phenotype is dominant or recessive
  2. chromosomal location of gene locus
    • autosome
    • sex chromosome (X or Y)
    • mitochondrial genome
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18
Q

Does the mitochondrial genome follow Mendelian inheritance?

A
  • No
  • always inherited from mother
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19
Q

What are the four major patterns of Mendelian inheritance?

A
  1. autosomal recessive
  2. autosomal dominant
  3. X-linked dominant (very rare)
  4. X-linked recessive
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20
Q

Autosomal recessive disease genotype:

A
  • must have two mutant alleles and no wild type
    • the type of mutation in each allele can be different (i.e. compound heterozygote)
  • rare
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21
Q

Effect of mutant alleles in autosomal recessive disorders:

A
  • reduce or eliminate function of gene product
  • often affect enzyme function
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22
Q

What type of inheritance is this?

(b is mutant allele)

A

autosomal recessive

  • bb has disease phenotype
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23
Q

Risk that a child of either sex will be affected in autosomal recessive inheritance:

A

1/4 (25%)

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24
Q

Risk that a child of either sex will be a healthy carrier in autosomal recessive inheritance:

A

1/2 (50%)

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25
Risk that a child of either sex **_will not be affected_** in autosomal recessive inheritance:
3/4 (75%)
26
Four factors that affect the risk of inheritance of a autosomal recessive disorder:
1. carrier frequency (how prevalent carriers are) 2. consanguinity (closely related) 3. inbreeding (small population) 4. genetic isolates
27
What are the five key features of an autosomal recessive pedigree?
1. parents unaffected carriers 2. males = females 3. recurrence risk to unborn sibling of an affected individual is 25% 4. phenotype found in siblings 5. rare trait = likelihood of consanguineous mating
28
What type of inheritance is this? | (B is mutant allele)
autosomal dominant only need one copy of mutant allele to have phenotype
29
Risk that a child of either sex **_will be affected_** in autosomal dominant inheritance:
1/2 (50%)
30
Autosomal dominant disease genotype:
* only need one mutant allele to have phenotype
31
What type of pedigree is this?
autosomal recessive * parents are unaffected carriers
32
What type of pedigree is this?
autosomal dominant * every affected individual has an affected parent * no skipping of generations
33
Four features of autosomal dominant pedigree:
1. every affected individual has an affected parent; no generation skipping. 2. males and females equally affected. 3. about 1/2 of offsprign of affected individual affected. 4. normal siblings of affected individuals have all normal offspring.
34
In what Mendelian inheritance pattern can male-to-male transmission occur?
autosomal dominant
35
Incomplete dominance definition:
* a form of autosomal dominant inheritance * individual homozygous for autosomal dominant mutation will be **_more severely_** affected than individuals heterozygous for autosomal dominant mutation * note: homozygous AD mutations are rare
36
What type of inheritance is this? | (B is mutant allele)
incomplete dominance * BB more severely affected than Bb
37
Risk that a child of either sex **_will be affected_** in incomplete dominance inheritance:
* 3/4 (75%) * a form of autosomal dominant inheritance
38
How do you determine whether an X-linked inheritance is dominant or recessive?
* look at phenotype in heterozygous woman * no phenotype = recessive * phenotype = dominant
39
What type of inheritance is this? | (Green X is mutant allele)
X-linked recessive inheritance (female carrier parent) * offspring females 1/2 chance of carrier * offspring males 1/2 chance of affected
40
What type of inheritance is this? | (Green X is mutant allele)
X-linked recessive inheritance (affected male parent) * all female offspring carriers (obligate) * all normal male offspring
41
What type of inheritance has male-to-male transmission?
* autosomal dominant
42
Can X-linked recessive inheritance have male-to-male transmission?
NO
43
In X-linked recessive inheritance, what is the one situation where a carrier female will express some phenotype?
* when she has unbalanced X-inactivation
44
What type of pedigree is this?
X-linked recessive * males exclusively affected\* * \*unless unbalanced X-inactivation in heterozygous female
45
Four features of X-linked recessive inheritance:
1. males exclusively affected\* * \*unless unbalanced X-inactivation in females 2. Gene transmitted from affected male to all daughters 3. Mutant allele may be transmitted through a series of carrier females
46
Distinguishing features of X-linked dominant inheritance:
1. trait never passed from father to son 2. affected father and normal female parents will have: * all affected daughters * all normal sons
47
What type of pedigree is this?
X-linked dominant * all daughters of affected male are affected * all sons of affected male are normal
48
What types of genotype does phenotype occur in dominant inheritance?
* homozygote and heterozygote * homozygotes more severely affected
49
What types of genotype does phenotype occur in recessive inheritance?
* homozygote, hemizygote, compound heterozygote
50
What type of inheritance pattern are males and females equally affected?
autosomal dominant and autosomal recessive
51
What type of inheritance pattern are males affected much more than females?
X-linked recessive
52
What type of inheritance pattern are females affected more than males?
X-linked dominant
53
Reduced penetrance definition:
* when the probability that a mutant gene will have a phenotypic expression is less than 100% * "all or none" phenotype
54
Variable expressivity definition:
* when the severity of expression of the phenotype among individuals with the same disease-expressing genotype is different
55
Sex-limited traits definition:
* when autosomal mutations are inherited by both sexes, but the phenotype is only evident in one sex * due to anatomical or physiological differences
56
Male-limited precious puberty is a form of what type of inheritance?
* autosomal dominant sex--limited phenotype * only boys affected
57
Hemochromatosis is a form of what type of inheritance?
autosomal recessive sex-limited trait * more common in males * a disease caused by excess iron * females rid excess iron through pregnancy and menstruation
58
Mosaicism definition:
* the presence of two or more populations of cells with different genotypes in one individual who has developed from a single fertilized egg. * pure somatic * pure germline
59
How to determine germline mosaicism:
* both parents normal and test negative for being carriers; more than one child affected with a highly penetrant AD or XL-R disorder * all gametes of one parent are affected
60
Genetic lethal definition:
* diseases that are produced by dominant alleles with effects so severe that persons with them do not have children
61
Seven factors that create exceptions to Mendelian rules:
1. Reduced penetrance 2. Variable expressivity 3. Sex-limited traits 4. Germ-line mosaicism 5. Genetic Imprintng 6. New Mutations 7. Misattributed Paternity
62
Genomic imprinting definition in regard to inheritance:
* when the sex of the transmitting parent plays a role in the expression of the phenotype in affected children * "parent of origin" specific pattern is present in all somatic cells, but reversed in germ cells
63
Genetic imprinting (methylation) is reversed in:
the gametes
64
Two most common disorders which arise from genetic imprinting affecting pedigrees:
1. prader-willi 2. angelman syndrome **DELETIONS OCCUR ON SAME REGION OF CHROMOSOME 15**
65
Prader-Willi syndrome:
* loss of paternally inherited gene * 20 maternally imprinted genes affected * excessive weight gain, motor and developmental delays
66
Angelman syndrome:
* loss of maternally inherited gene * one paternally imprinted gene is affected * severe mental retardation/happy/non-verbal

BMS2.01 Single Gene Inheritance (CORBETT) (2 decks)

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