Phenotypic Variability Flashcards

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1
Q

What is meant by phenotypic variability?

A

variation of gene expression in the same disease in different individuals, such that individuals with the same genetic disease may not have the same symptoms or presentations

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2
Q

What are the 5 reasons as to why phenotypic variablity exists? MUMES

A

Mutations
Unstable
Modifiers
Environment
Sex

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3
Q

What is meant by modifiers?

A

When the expression of one gene directly affects the presence of other genes

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4
Q

What is meant by the effects of mutations on the phenotype of a disease?

A

Different subtypes of the same disease have different presentations, due to mutations within the same gene

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5
Q

What is an example of how sex affects the phenotype of a disease?

A

In hereditary haemochromatosis - women lose blood through mensturation and therefore generally have lower iron levels

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6
Q

What is an example of how mutations affect the phenotype of a disease?

A

Duchenne vs Becker muscular dystrophy - slightly different mutations of the same gene cause different presentations

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7
Q

What is an example of how modifiers affect the phenotype of a disease?

A

In CF, the variety of genes present can increase the degree of CF

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8
Q

What are trinucleotide repeat disorders?

A

Where an increased number of nucleotide repeats (>27) cause more severe phenotypes throughout generations

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9
Q

What affect do trinucleotide repeats have on the proteins produced?

A

Changes protein function

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10
Q

What does a larger number of trinucleotide repeats result in?

A

More severe phenotype and earlier onset of disease

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11
Q

If you have less than how many TNR’s is the mutation considered stable?

A

Less than 27

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12
Q

If individuals are identical, and there is variation in the phenotype, what is likely to have caused the variation?

A

The environment

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13
Q

In non-identical individuals with the same mutation, what could cause the variation in phenotype?

A

The presence of other genes as well as the environment

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14
Q

In unrelated individuals, how does phenotypic variability arise?

A

Due to unstable mutations like TNRs

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15
Q

If there is a binary presentation of a condition eg half a family have a condition and half don’t, what is likely to cause the variation?

A

The presence of a second gene modifying the disease phenotype

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16
Q

If there are two forms of the same disease, and one is a milder phenotype, what is likely to cause the variation?

A

Mutations - Different mutations of the same gene results in different diseases

17
Q

When there is wide variation in a condition but the variation does not apply to monozygotic twins, what is likely to be causing the variation?

A

A second gene which the twins did not inherit

18
Q

When there is marked variability and no two members being affected in the same way, what is likely to cause the variation?

A

Environment

19
Q

When there is a large difference in the age of onset between family members, what is likely to cause this variation?

A

Unstable mutations

20
Q

What cause of variation is more likely to have transgenerational effects?

A

The expansion of unstable trinucleotide repeats