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Genomics SGUL Sem 3 > Inheritance Patterns > Flashcards

Inheritance Patterns Flashcards

1
Q

What is the symbol for a male on a pedigree?

A

A square

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2
Q

What is the symbol for a female on a pedigree?

A

A circle

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3
Q

How do you show that two people are partners on a pedigree?

A

There is a line between them

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4
Q

How do you show children on a pedigree?

A

There is a line down

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5
Q

How do you show siblings on a pedigree?

A

There is a line above connecting them from the top

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6
Q

How do you show affected people on a pedigree?

A

They are coloured in

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7
Q

How do you show carriers on a pedigree?

A

A shaded dot within the shape

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8
Q

How do you show a consanguineous couple on a pedigree?

A

Double line joining them

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9
Q

What is a stillborn baby of unknown sex on a pedigree?

A

A rhombus with the SB symbol

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10
Q

How is a spontaneous abortion shown on a pedigree?

A

A triangle

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11
Q

How is a therapeutic abortion shown on a pedigree?

A

A triangle with a line through it diagonally

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12
Q

How are twins shown on a pedigree?

A

Two shapes coming from the same vertical line

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13
Q

How is pregnancy shown on a pedigree?

A

A rhombus with a P inside it

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14
Q

What is a rhombus on a pedigree?

A

Unaffected person whose sex is unknown

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15
Q

How do autosomal dominant conditions manifest?

A

Heterozygous form

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16
Q

What are the 5 key things to look for in an autosomal dominant pedigree?

A

→ Multiple generations affected
→ Both sexes
→ Male to female and female to male transmission
→ Most will have an affected parent
→ If both parents possess the trait, but it is absent in any of their offspring, then the parents are both heterozygous (“carriers”) of the recessive allele

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17
Q

How do you know that an autosomal dominant condition is not carried on the sex chromosome?

A

Both genders are affected
Transmission between sexes

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18
Q

What is the risk for each child of an affected parent with an autosomal dominant condition?

A

50% risk

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19
Q

What is penetrance?

A

% of individuals who carry the mutation and develop symptoms of the disorder

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20
Q

What does a 75% penetrance mean?

A

Someone can have the dominant allele but not phenotypically have the disease e.g. Huntingtons

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21
Q

What is variable expressivity?

A

Variation in the severity/symptoms of the disorder

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22
Q

What is a condition that exhibits variable expressivity?

A

Neurofibromatosis I

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23
Q

What is somatic mosaicism?

A

New mutation arises at an early stage of embryogenesis

Present in some tissues or cells

If the majority of cells are not affected then the disease severity is reduced

24
Q

What is germ line mosaicism?

A

New mutation arises during oogenesis or spermatogenesis.

Mutation present in variable proportion of gametes.

Some gametes will have the mutation and some will not

25
Q

Which type of mosaicism can be transmitted to offspring?

A

Germ line mosaicism

26
Q

What is anticipation and what kind of disorders does this occur in?

A

Worsening of the disease severity in successive generations

Occurs in triplet repeat disorders

27
Q

How do autosomal recessive conditions manifest?

A

Homozygous
Compound heterozygous

28
Q

What are the key things to look for in an autosomal recessive pedigree?

A

→ Both sexes affected
→ One generation affected
→ can be consanguinity
→ Affected individual does not have affected parents
→ Carriers (heterozygote) not affected

29
Q

What is a compound heterozygote?

A

2 mutations are in the same gene

Mutations are different

Vast majority of recessive is compound heterozygosity

30
Q

What is a homozygote?

A

2 mutations in the same gene
Identical mutations

31
Q

What is an example of different mutations in genes in a compound heterozygote? (cystic fibrosis)

A

→ delta F508
→ G542X

32
Q

What is an example of the same mutation in genes in a homozygote? (cystic fibrosis)

A

→ Delta F508
→ Delta F508

33
Q

What are features of autosomal recessive inheritance?

A

→ Found in clusters of siblings but not in parents and offspring
→ All offspring of affected person are obligate carriers

34
Q

What is the carrier probability for autosomal recessive inheritance?

A

2/3 for unaffected siblings of affected person

35
Q

What is the recurrence risk for autosomal recessive inheritance?

A

1/4 for each sibling of the affected person

36
Q

What are the 2 features of X linked recessive inheritance?

A

→ Women are unaffected carriers
→ no male to male transmission

Hemizygous - loci on X-chromosome in men

37
Q

What are the 2 features of X linked dominant inheritance?

A

→ Women are affected
→ Males are more severely affected/lethal

38
Q

Why can women be homo or heterozygous for X linked inheritance?

A

They have 2 copies of the X chromosome

39
Q

Why can men not be homo or heterozygous?

A

They only have a single copy of the X linked gene

40
Q

How are X linked genes never passed?

A

Never passed from father to son

41
Q

What are all daughters of affected males with an X linked inheritance?

A

Obligate carriers

42
Q

What is skewed X inactivation?

A

→ The majority of genes on a woman’s X chromosome are inactivate
→ One of the X chromosomes are inactivated in all the cells
→ The healthy X chromosome is switched off more often than not so the mutated protein is expressed

43
Q

What is an example of manifesting carriers in X linked disorders?

A

→ Some women have symptoms
→ Cardiomyopathy in DMD (Duchenne muscular dystrophy)

44
Q

What is Y linked inheritance always passed from and to and what is an example of this?

A

→ Father to son
→ Hirsutism

45
Q

What is a mutation?

A

A change in genetic material

46
Q

What is a pathogenic mutation?

A

Results in an alteration of the function of the gene product which causes a disease phenotype

47
Q

What are 3 types of mutations?

A

→ Substitutions
→ Deletions
→ Insertions

48
Q

What is a silent/synonymous change?

A

A nucleotide change without an amino acid change

49
Q

What is a missense mutation?

A

→ Replacement of a single nucleotide
→ Incorrect amino acid gets produced

50
Q

What is the impact of amino acid substitution?

A

→ Physiochemical similarity between two amino acids
→ Functional role of a specific domain of protein

→ Phylogenetic conservation of amino acid amongst diverse species

51
Q

What is a nonsense mutation?

A

→ Replacement of a nucleotide
→ Stop codon is produced
→ Shortening of protein

52
Q

What does an insertion mutation do?

A

Incorrect amino acid sequence

53
Q

What types of insertion are there?

A

In frame (multiple of 3)
Frameshift (not a multiple of 3)

54
Q

What types of deletion are there?

A

In frame (multiple of 3)
Frameshift (not a multiple of 3)

55
Q

What do most autosomal dominant disorders show?

A

Age-dependant penetrance. As one gets older, they show symptoms. BRCR 1 breast cancer

56
Q

What is reduced penetrance?

A

Reduced penetrance- individuals carry mutation but do not show symptoms

57
Q

Why are frameshift deletions more dangerous than in-frame?

A

Extremely likely to lead to large-scale changes to polypeptide length and chemical composition, resulting in a non-functional protein that often disrupts the biochemical processes of a cell.

Genomics SGUL Sem 3 (21 decks)

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