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The human genome > Pedigrees + inheritance (just key stuff) > Flashcards

Pedigrees + inheritance (just key stuff) Flashcards

1
Q

What is autosomal linkage?

A

When it is located on an autosome (chromosome 1-22)

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2
Q

What it X-linked/Y-linked?

A

Gene located on the X or Y chromosome

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3
Q

What is a locus?

A

The position/site on a chromosome where a gene is located

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4
Q

What is an allele?

A

Alternate forms of a gene

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5
Q

What is a heterozygote?

A

Different alleles at the same locus

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6
Q

What is a homozygote?

A

Identical alleles at the same locus

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7
Q

What is a genotype?

A

An individual’s genetic constitution

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8
Q

What is a phenotype?

A

Observed effect of the action of a gene or genes

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9
Q

What is a propositus vs a proposita?

A

Propositus = A male index case

Proposita = A female index case

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10
Q

What are the 5 patterns of inheritance that we cover?

A
  • Autosomal Dominant
  • Autosomal Recessive
  • X-linked Recessive
  • X-linked dominant
  • Maternal (mitochondrial)
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11
Q

What are the characteristics of autosomal dominant inheritance?

A
  • Found in heterozygous stae
  • Transmitted from one generation to next
  • Can arise thru new mutation
  • Can be followed in family tree
  • Usually affects males & females equally
  • Have a 1 in 2 chance of inheriting from the affected parent
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12
Q

Give examples of Autosomal Dominant diseases:

A
  • Myotonic Dystrophy
  • Huntington’s disease
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13
Q

What are the characteristics of Autosomal Recessive inheritance?

A
  • Heterozygotes are healthy –> carriers
  • Mutation present in homozygous (double dose of mutation)
  • Often cannot be followed in family tree
  • Affects males & females equally
  • If parents heterozygous for same autosomal recessive condition = offspring 1 in 4 chance of inheriting
  • For rare autosomal recessive alleles –> parents of a homozygous may be consanguineous
  • Affected person usually born to unaffected parents (parents usually asymptomatic carriers)
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14
Q

What does consanguineous mean?

A

Mating between 2 closely related relatives

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15
Q

Give an example of an Autosomal Recessive mutation:

A

Cystic Fibrosis

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16
Q

What happens is a homozygote & a heterozygote for an Autosomal recessive condition mate?

A

The condition may appear as dominant as children will either be affected or carriers

(in reality the condition is recessive but high chance of inheriting in this fmaily)

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17
Q

What are the 3 ways heterogeneity can occur?

A
  • Locus
  • Allelic
  • Clinical
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18
Q

What is clinical Genetic Heterogeneity?

A

Mutations in the same gene that leads to 2 or more different genetic conditions

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19
Q

What is allelic Genetic Heterogeneity?

A

Differnt mutations within a given gene give rise to the same condition

(Mutation at point 1 or 2 on the gene but both = same condition phenotypically

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20
Q

What is locus Genetic Heterogeneity?

A

Same clinical phenotype reuslts from mutations at any one of several different loci

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21
Q

When can double heterozgyotes arise?

A

Double heterozygous parents can lead to a homozygous individual w a mutant allele but at a different locus

e.g. there are at least 16 loci that cause sensorineural deafness

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22
Q

What is a compound heterozygote?

A

Where there are 2 different mutations at the same locus

23
Q

What are X-linked recessive mutations determined by?

A

Determined by a gene on the X-chromsome

24
Q

What are the characteristics of an X-linked recessive inheritance?

A
  • Traits usually only show in males (as males have 1 X chromosome)
  • Male w a mutant X is hemizygous
  • X-linked disorder is transmitted by heterozygous female carries to affected males
  • 1 in 2 males from carrier females affected
  • Affected males may transmit to carrier daughters but NOT sons (sons inherit Y from father = no transmission)
  • Pedigrees can show ‘diagonal’ or ‘knights’ move transmission
  • Mother is typically aymptomatic carrier
25
Q

Can male-to-male tranmission occur in X-linked recessive disorders?

A

No male to male transmission

Bc son will inherit Y from dad so cannot physically pass on the disorder

26
Q

Give examples of X-linked recessive disorders:

A
  • Duchenne muscular dystrophy
  • Fragile X syndrome
  • Haemophillia
27
Q

How can females be affected by X-linked recessive disorders?

A

If the father is affected & the mother is a carrier

Or

Nonrandom X-inactivation

28
Q

Read thru other possibilities for X-linked recessive disorders

A

Bottom of page 10 notes

29
Q

What are the characteristics of a X-linked Dominant inheritance?

A
  • Males & females may be affected –> demales more common (bc 2 copies of X chromosome)
  • Females usually less severely affected than males
  • Affected females transmit to BOTH sons & daughters
  • Affected males transmit to all daughter but NOT SONS (give sons Y chromosome)
  • Child of an affecte female, regardless of its sex, had 50% chance of being affected
30
Q

Give an example of X-linked Dominant Inheritance:

A

Vitamin D Resistance Rickets

31
Q

What are the characteristica of maternal (mitochondrial) inheritance?

A
  • Mithcochondrial inheritance –> expected to be inhertied from mum as all mitochondria inherited from motehr
  • Maternally inherited so will affect BOTH males & females
  • Note–> incomplete penetrance of phenotype in some examples (due to multiple type of mitochondria (multiple types inherited) - due to different levels of mutations, some individuals might recieve more mutant copies than others)
32
Q

What are the 4 other considerations we must make in pedigrees?

A
  • Pleiotrophy
  • Variable expressivity
  • Penetrance
  • Reduced/incomplete penetrance
33
Q

What is Pleiotrophy?

A

When a single gene affects multiple traits or charateristics in an organism

34
Q

What is Variable Expressivity?

A

Means that the same gene mutation can show up differently in person to person

(Variation in phenotype)

35
Q

What is Pentrance?

A

How likely a gene mutation is to show up in someone

(The proportion of heterozygotes for a dominant gene who express a trait, even if mildly)

36
Q

What is reduced/incomplete penetrance?

A

Means even with a gene mutation, some ppl may not show the expected traits

(A condition where some heterozygotes with a mutation cannot be detected clinically. An individual who is heterozygous for a dominant mutation but shows no symptoms represents non-penetrance)

37
Q

What are the 3 main mutation classes?

A
  • Deletions
  • Insertions
  • Single base substitutions
38
Q

What are the 5 types of singe base substitutions?

A
  • Missense mutations
  • Nonsense mutations
  • Splice site mutations
  • Frameshift mutations
  • Dynamic mutations
39
Q

What are missense mutations?

A

Replace one amino acid with another in the gene product

40
Q

What are nonsense mutations?

A

Replaces an amino acid with another in the gene product

41
Q

What is a splice site mutation?

A

Creaste or destroy signals for exon-intron splicing

42
Q

What is a frameshift mutation?

A

Can be produced by deletions, insertions or splicing errors

43
Q

What is a dynamic mutation?

A

Tandem repeats that often change size on transmission to children

44
Q

What are the 4 mutation functional types?

A
  • Gain-of- function
  • Dominant-Negative
  • Loss-of-function
  • Haploinsufficiency
45
Q

What is a gain of function mutation type?

A

A mutation which produces a NEW FUNCTION in the resulting gene product

46
Q

What is a dominant negative mutation type?

A

A mutation (which in the heterozygous state) results in the LOSS OF FUNCTION/ ACTIVITY of the mutant gene product

This interferes w the function of the gene product from the normal allele (mutant gene distrupts function of the normal gene)

47
Q

What is a loss of function mutation type?

A

Mutation which causes absent or REDUCED activity of the gene product

48
Q

What is a haploinsufficiency mutation type?

A

Mutations in which the heterozygote state produce HALF THE NORMAL LEVELS of a gene product

Results = ina mutant phenotype i.e. dosage sensitivity

49
Q

How is linkage analysis used?

A

No longer used in human genome mapping

Some utility in rare disease gene recovery & risk assessment

Still useful in finding genes in non-human organisms

50
Q

What does linkage describe?

(Linkage analysis)

A

It describes the cosegregaation of genetic variants htat are close to each other

51
Q

Where will linked markers be found?

(Linkage analysis)

A

Linked markers will be on the same chromosome & close together

52
Q

What would stop linked markers from cosegregating?

(Linkage analysis)

A

Linked markers will cosegregate unless a recombination separates them

53
Q

Tighter linkage = ?

A

The tighter linkage = the less recombination there is between them

The human genome (20 decks)

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