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Inheritance Patterns Flashcards

1
Q

Male shape

A

Square

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2
Q

Female shape

A

Circles

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3
Q

Partners shape

A

Line between the shapes

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4
Q

Siblings shape

A

Line above them

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5
Q

Children shape

A

Line down

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6
Q

Affected people

A

Shaded

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7
Q

Carriers

A

Dots

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8
Q

Double line represents…

A

Union of consanguineous couple

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9
Q

Stillborn baby

A

Diamond with SB

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10
Q

Spontaenous abortion

A

Triangle

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11
Q

Therapeutic abortion

A

Triangle with line

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12
Q

Non-identical Twins

A

Diamond line

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13
Q

Identical twins

A

Line closing diamond

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14
Q

Unknown shape

A

Diamond shape

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15
Q

No offspring

A

Double line

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16
Q

Define autosomal dominant

A
  • Mainfest in Heterozygous form
  • Homozygous is lethal
  • Multiple generations affected
  • Both sexes affected (not sex-linked)
  • Male to female and female to male transmission
  • Affected parent -> dominant conditions are heterzoygous, only need one allele copy
  • May rely on transmissions
  • May rely on de novo mutations
  • 50% risk to offspring
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17
Q

Characteristics of autosomal dominant

A
  • Most individuals have an affected patient
  • Males and females are equally likely to inherit the allele and be affected.
  • Risk for each child of an affected parent is 1/2.
  • If an affected individual’s siblings/children are not affected, and they do not carry the mutation they cannot pass it on to their own offspring.
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18
Q

What is penetrance?

A

Percentage of individuals who carry the mutation and develop symptoms of the disorder. (May have the genotype but not expressed phenotypically)

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19
Q

Age-dependent penetrance

A

Individuals may develop the conditions later in life.

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20
Q

Incomplete penetrance

A

Mutant allele but not having the disease can be due to the interaction of the environment or hormonal protection from conditions.

21
Q

How is penetrance calculated?

A

By the number of individuals and divide by the number of people with the genotype. There are very few diseases that are 100% penetrant.

22
Q

Features of autosomal dominant inheritance

A
  • Penetrance
  • Variable expressivity
  • New mutation rate
  • Somatic mosaicism
  • Germ-line mosaicism
  • Anticipation
23
Q

What is variable expressivity?

A

Variation in severity/symptions of disorder between individuals with the same mutation e.g. neurofibromatosis type 1

24
Q

What is new mutation rate feature in ADI?

A

De novo mutation rate varies considerably between AD conditions

25
What is somatic mosaicism feature in ADI?
New mutation arising at early stage in embryogenesis | - Present in only some tissues/cells
26
What is germ-line mosaicism feature in ADI?
New mutation arises during oogenesis or spermatogenesis
27
What is anticipation in ADI?
worsening of disease severity in successive generations | - Occurs in triplet repeat disorders/expansion disorders
28
Define autosomal recessive inheritance
- Both copies of the gene are affected for the condition to be present - Manifest in homozygous/compound heterozygous form - Carriers (heterozygote) not affected - Both sexes affected - Male to female and female to male transmission - Usually one generation affected - May be consanguinity e.g. cousin marriages
29
What is compound heterozygote in ARI?
2 mutations in the same gene and the mutations are different
30
What is homozygote in ARI?
2 mutations in the same gene and the mutations are identical which may suggest consanguinity
31
Example of compound heterozygote
Deletion at position 508 on the cystic fibrosis gene. Two different mutations can cause cystic fibrosis
32
atures of ARI
- Trait often found in clusters of siblings but not in parents and offspring (unlike dominant inheritance which is seen in multiple generations) - Recurrence risk = 1/4 for each sibling of affected person - Carrier probability = 2/3 for unaffected siblings of affected person - All offspring of affected person are obligate carriers - 25% affected, 50% carriers, 25% unaffected
33
Define X-linked inheritance
In women, can be homozygous or heterozygous as two copies of X-linked genes In men, hemizygous because only one single copy of X-linked genes.
34
Where does recessive X-linked inheritance occur?
Women are carriers + unaffected | No male to male transmission - men will give their Y chromosome to son
35
Where does dominant X-linked inheritance occur?
Women are affected | Males more severly affected/lethal.
36
What are some important aspecfts of X-linked recessive inheritance?
- X-linked genes are never passed from father to son. - All daughters of affected males are obligate carriers. - Children of carrier females have a 50% chance of inheriting mutant allele.
37
What is skewed X-inactivation?
The healthy X-chromosome is switched off. A smaller proportion of cells will have less of the healthy X chromosome and more will have the unhealthy X chromosome even if the condition is homozygous. This leads to manifesting carriers.
38
What are manifesting carriers?
Having some symptoms in X-linked recessive conditions e.g. cardiomyopathy in DMD
39
What is Y-linked inheritance?
Always and only passed from fathers to sons
40
Mutation
A change in the genetic material
41
Pathogenic mutation
An alteration of the function of the gene product and can cause a disease phenotype.
42
What types of mutations are there?
Substitutions (point mutations) Deletions Insertions
43
Where are mutations found?
In coding DNA | Non-coding DNA (such as promoters and introns)
44
What is a silent or synonymous base substitutions?
Nucleotide change without amino acid change; synonymous substitution
45
What is a point mutation - missense?
Base substitution and the amino acid result is a missense change. A change in the bases results in the change of the amino acids.
46
What is a nonsense point mutation?
- Introduction of a stop codon resulting in a truncated protein. - Can cause removal of functional parts of protein - However, mRNA strand can sometiems be degraded via nonsense mediated decay.
47
Two types of indels
In Frame (multiple of three) or Frameshift (not multiple of three)
48
What type of mutation is a frameshift?
Can be pathogenic

Genomics (19 decks)

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