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Genomics > Inheritance Patterns > Flashcards

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
Q

What is somatic mosaicism feature in ADI?

A

New mutation arising at early stage in embryogenesis

- Present in only some tissues/cells

26
Q

What is germ-line mosaicism feature in ADI?

A

New mutation arises during oogenesis or spermatogenesis

27
Q

What is anticipation in ADI?

A

worsening of disease severity in successive generations

- Occurs in triplet repeat disorders/expansion disorders

28
Q

Define autosomal recessive inheritance

A
  • 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
Q

What is compound heterozygote in ARI?

A

2 mutations in the same gene and the mutations are different

30
Q

What is homozygote in ARI?

A

2 mutations in the same gene and the mutations are identical which may suggest consanguinity

31
Q

Example of compound heterozygote

A

Deletion at position 508 on the cystic fibrosis gene. Two different mutations can cause cystic fibrosis

32
Q

atures of ARI

A
  • 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
Q

Define X-linked inheritance

A

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
Q

Where does recessive X-linked inheritance occur?

A

Women are carriers + unaffected

No male to male transmission - men will give their Y chromosome to son

35
Q

Where does dominant X-linked inheritance occur?

A

Women are affected

Males more severly affected/lethal.

36
Q

What are some important aspecfts of X-linked recessive inheritance?

A
  • 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
Q

What is skewed X-inactivation?

A

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
Q

What are manifesting carriers?

A

Having some symptoms in X-linked recessive conditions e.g. cardiomyopathy in DMD

39
Q

What is Y-linked inheritance?

A

Always and only passed from fathers to sons

40
Q

Mutation

A

A change in the genetic material

41
Q

Pathogenic mutation

A

An alteration of the function of the gene product and can cause a disease phenotype.

42
Q

What types of mutations are there?

A

Substitutions (point mutations)
Deletions
Insertions

43
Q

Where are mutations found?

A

In coding DNA

Non-coding DNA (such as promoters and introns)

44
Q

What is a silent or synonymous base substitutions?

A

Nucleotide change without amino acid change; synonymous substitution

45
Q

What is a point mutation - missense?

A

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
Q

What is a nonsense point mutation?

A
  • 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
Q

Two types of indels

A

In Frame (multiple of three) or Frameshift (not multiple of three)

48
Q

What type of mutation is a frameshift?

A

Can be pathogenic

Genomics (19 decks)

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