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Mcb1 > THe Human Genome > Flashcards

THe Human Genome Flashcards

1
Q

How is mitochondrial DNA inherited?

A

Maternally

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2
Q

Describe the nuclear genome

A 
Linear DNA organized in chromosomes
2 copies per cell
3.1 *10^9 by per haploid genome
23 pairs ( 22 autosomal and 1 sex)
~23000 genes
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3
Q

What pair of sex chromosomes makes a male/female?

A

Females: XX
Male: XY

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4
Q

Describe the mitochondrial genome

A 
Circular DNA
Many copies per mitochondria
~16.5k by per genome
37 genes
No histones
Inherited Maternally *
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5
Q

What genes are expressed in all cells?

A

Housekeeping genes

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6
Q

What controls cell differentiation?

A

Genes

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7
Q

How are pedigrees labeled?

A

Generations re indicated with Roman numerals

Individuals are identified within each generation numbered left to right

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8
Q

What is the proband?(propósitus or index case)

A

The first person identified to have a genetic disorder in a family

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9
Q

What is a consultant?

A

An unaffected individual seeking counseling

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10
Q

Are multiple probands possible?

A

Yes, if the disease was ascertained by more than one source

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11
Q

What is the degree of relationship in a first degree relation ship? Name some examples

A

50% of genes
I.e. Parent, sib, child
(One step away from person of interest)

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12
Q

What is the degree of relationship in 2nd degree relationships? Name some examples

A

25% genes in common
I.e. Aunt, uncle, niece, grand-parents, half-sib
(Two steps away from person of interest)

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13
Q

What is the degree of relationship in a 3rd degree relationship? Name some examples

A

12.5% of genes in common

I.e. First cousins ( 3 steps away from person of interest)

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14
Q

With every increase of the degree of relationship the % of genome in common how much?

A

50%

I.e 1st : 50%, 2nd: 25%, 3rd: 12.5%, 4th: 6.25%

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15
Q

What are choreiform movements?

A

Involuntary, jerky movements, facial grimacing

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16
Q

What are the signs of huntingtons?

A

Forgetful, depressed, restless and choreiform movements

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17
Q

What is the inheritance of Huntington disease?

A

Autosomal Dominant

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18
Q

What brain tissue shrinks in Huntington disease?

A

Caudate nucleus

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19
Q

What are the characteristics of Autosomal Dominance (AD) inheritance?

A

Affected parent has 50% chance of passing to offspring
Successive generations are affected (vertical transmission)
M/F equally affected
M/F transmit disease equally
M to M transmission occurs

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20
Q

For AD diseases where does the spontaneous mutation occur?

A

In meiosis of one of the parents. Usually siblings re very unlikely to be affected

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21
Q

Name some AD diseases

A 
Huntington Disease
Marcan Syndrome 
Achondroplasia
Osteogenesis Imperfecta
Neurofibromatosis 
Polycystic Kidney Disease (ADPKD)
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22
Q

What is penetrance?

A

The probiotic that individuals with a specific genotype will manifest the corresponding phenotype
All or none

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23
Q

What is incomplete penetrance?

A

Occurs when some individuals with a genotype do not manifest the corresponding phenotype
I.e generation skipping or BRCA1 for breast cancer

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24
Q

What is variable expressivity?

A

Variation in phenotype of same gene

Observed as variation in: which symptoms present and severity

25
Q

What is cystic fibrosis confirmed by?

A

The sweat test

Na+ in sweat > 60 mM (upper limit of normal range)

26
Q

What are the clinical features of Cystic fibrosis?

A 
Lung disease
Lung infections
Malabsorption
Salty sweat
Male infertility
Meconium ileus (obstruction of si due to thickening of meconium)
27
Q

What are the characteristics of AR inheritance?

A

W/ both parents being carriers: 25% of offspring affected
Horizontal pattern on pedigree ( one generation)
M/F are affected equally
M/F transmits disease equally
M2M transmission

28
Q

Name some examples of AR diseases.

A 
Many metabolic disorders
-E.g. Alkaptonuri, Phenylketonuria (PKU), Oculocutaneous Albanism, Lysosomal Storage disease
Cystic fibrosis
Thalassemia
Sickle Cell Disease
29
Q

What was found in case 3 when Nazarene failed her 8 month hearing after normal milestones were previously met.

A

Profound hearing loss

-her case was an AR negative

30
Q

What is consanguinity?

A

Mating between individuals who are 5th degree or closer relatives
-e.g great great grandparents and closer

31
Q

What does consanguinity cause?

A

An increase in genetic disease probability for offspring.

-the closer the relationship, the more likely AR phenotype will be expressed

32
Q

What are the abnormalities in incestuous matings?

A 
Intellectual
-25% severe, 35% mild
Autosomal recessive disorder
-10-15%
Congenital malformation 10%
33
Q

What is a pseudominance?

A

A recessive trait mimics a dominant pattern

-i.e. O type blood, blue eyes, sickle cell in parts of Africa, cystic fibrosis in parts of Quebec

34
Q

When can pseudodominance occur?

A

When a recessive gene is very common and a homozygous might mate with a heterozygous resulting in vertical transmission

35
Q

What is complementation?

A

Mating between individuals with the same phenotype results in offspring without the phenotype due to mutations in different genes
I.e. The offspring are heterozygous in both genes

36
Q

What is an example of complementation?

A

The gene for Congenital hearing loss

37
Q

What is the 2/3 rule?

A

For traits inherited in an autosomal recessive manner, an unaffected sibling of an affected individual has a 2/3 risk of being a carrier

38
Q

When can the 2/3 rule be applied?

A

In an autosomal recessive pedigree

  • can be ruled out that the sibling in affected
  • neither parent is affected
39
Q

What are some of the sign/symptoms of Duchene Muscular Dystrophy?

A
  • delayed motor milestones
  • Use gower’s maneuver
  • clumsy, first steps at 20month (late)
  • muscle s no dystrophin
40
Q

What are the characteristics of XR inheritance?

A

Males are faceted in multiple generations

  • NO male to male transmission
  • Generation skipping (through females)
41
Q

How often are the offsprings of XR patients affected?

A

Fathers: 0% of sons, 100% female carriers
Mothers:50% of sons defected, 50% of females are carriers

42
Q

What are obligate carriers?

A

Individuals who must be carriers based on logical analysis of a pedigree
-indicated by a dot on pedigree

43
Q

For XR, isolated cases may be due to what?

A

Spontaneous mutation

44
Q

What are some examples of XR diseases?

A
  • Duchenne muscular dystrophy
  • Hemophilia
  • Red-Green color blindness
  • Androgen insensitivity syndrome
  • Hunter syndrome
  • X-linked severe combined immunodeficiency
  • Menke’s disease
45
Q

What are the characteristics of XD inheritance?

A
  • No male to male transmission

- 2x F > M

46
Q

When XD reproduce, what offspring will be affected?

A
  • Affected mother will have 50% affected son and 50% affected daughters
  • Affected fathers will have no affected sons and ALL affected daughters
47
Q

What are some examples of XD diseases?

A
  • Rett syndrome
  • Fragile X syndrome (semi dominant)
  • Vitamin D-resistant rickets
  • Incontinentia pigmenti type 2
48
Q

What are son symptoms of Leber Hereditry optic neuropathy (LHON)?

A
  • blurred vision, loss of color distinction
  • retinal changes (optic disk swelling, tortuosity of retinal vessels)
  • progressive worsening of central vision
  • Maternal lineage has affected inidividuals
49
Q

What are the characteristics of mitochondrial pedigree?

A

Maternal inheritance

  • children of affected males are never affected
  • children of affected females are always affected (w/ reduced penetrance)
50
Q

What are some examples of Mitochondrial Diseases?

A
  • Leber hereditary optic neuropathy (LOHN)
  • Leigh syndrome (LS)
  • Mitochondril encephalomyopathy wth lactic acidosis and stroke-like episodes (MELAS)
  • Kearns-Sayre syndrome (KSS)
51
Q

What is mosaicism?

A

An individual who’s body contains two or more genetically distinct cell lines

52
Q

How does mosaicism occur?

A

Mutations that occur post-fertilization

53
Q

When is Mosaicism clinically important?

A
  1. Mutant cells have an increased growth tendency
  2. Mutation occurred early in embryogenesis and the mutant cell line make up a significant proportion of the body
  3. Mutation occurs in the Germline
54
Q

What is germline mosaicism?

A
  • mutation exists in the germline
  • may include other tissues
  • can be passed to offspring
55
Q

What is somatic mosaicism?

A
  • mutations that does not occur in the germline but can affect other tissues
  • can’t be passed down to offspring
56
Q

What are some implications of germline mosaicism?

A

My result in multiple affected children even when genetic testing of parent is Negative

57
Q

What are the implications of somatic mosaicism?

A

May result in disease is large enough proportion of cells are affected
-requires genetic testing if multiple tissues samples

58
Q

How can germline mosaicism cause confusion in pedigree?

A

In an asymptomatic couple w/ a child with a dominant disorder, all subsequent children will have increased risk of being affected by same disorder even if the parents are negative for mutation

59
Q

What questions should you ask yourself when you interpret a pedigree?

A
  1. Are there affecteds in multiple generations? (No = autosomal recessive)
    If yes, 2. M/F equally affected?
    If yes, 3. M to M transmission? (Yes= Autosomal dominant)
    If no, 3a. F>M? =XD
    If no, 3b. M>F? = XR

Mcb1 (13 decks)

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