Huntington's Disease Quiz

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Questions and Answers

What is the chance of children of a carrier female inheriting the mutant allele?

50% (correct)

25%

100%

75%

What is the typical outcome of X-inactivation in a woman's X-chromosomes?

All genes on both X-chromosomes are inactivated

Half of the genes on each X-chromosome are inactivated

All genes on one X-chromosome are inactivated

The majority of genes on one X-chromosome are inactivated (correct)

What is the term for the phenomenon where some women have some symptoms in X-linked recessive conditions?

Skewed X-inactivation

Manifesting carriers (correct)

Obligate carriers

Uneven X-inactivation

What percentage of women have uneven or skewed X-inactivation?

10% Signup and view all the answers

What is the consequence of skewed X-inactivation in some women?

They are more likely to exhibit symptoms of an X-linked recessive condition Signup and view all the answers

What is the term for the daughters of affected males who are carriers of the mutant allele?

Obligate carriers Signup and view all the answers

What is the Hardy-Weinberg equation used to estimate?

The frequency of the carrier state for an autosomal recessive trait Signup and view all the answers

What is the genotype of a male with respect to X-linked genes?

Hemizygous Signup and view all the answers

What is a characteristic of X-linked recessive inheritance?

No male to male transmission Signup and view all the answers

What is the reason for X-inactivation?

To ensure proper gene expression during embryonic development Signup and view all the answers

What is a characteristic of Autosomal Dominant Inheritance?

Variable Expressivity is observed Signup and view all the answers

What is unique about X-linked genes?

They are never passed from father to son Signup and view all the answers

What is the term for the worsening of disease severity in successive generations?

Anticipation Signup and view all the answers

When does Germ-line mosaicism occur?

During oogenesis or spermatogenesis Signup and view all the answers

What is the effect of X-inactivation on one of the X-chromosomes?

It is inactivated Signup and view all the answers

What is the result of a female being a carrier of an X-linked recessive trait?

She is unaffected Signup and view all the answers

What is the term for new mutations arising at an early stage in embryogenesis?

Somatic mosaicism Signup and view all the answers

What is the difference between a female and a male with respect to X-linked genes?

Females have two X-chromosomes and males have one Signup and view all the answers

What is the probability of an individual manifesting a disease with Autosomal Dominant Inheritance if they have a mutated gene?

100% Signup and view all the answers

What is the characteristic of Autosomal Recessive Inheritance?

Manifest in HOMOZYGOUS/COMPOUND HETEROZYGOUS form Signup and view all the answers

What is the probability of an individual being a carrier of an Autosomal Recessive disease if they have one mutated gene?

50% Signup and view all the answers

What is the characteristic of Autosomal Dominant Inheritance that results in an earlier age of onset?

Anticipation Signup and view all the answers

What is the term for the variation in severity or symptoms of a disorder between individuals with the same mutation?

Variable Expressivity Signup and view all the answers

What is the characteristic of Autosomal Recessive Inheritance that results in consanguinity?

May be consanguinity Signup and view all the answers

What is the characteristic of Y-linked inheritance?

It is always passed from fathers to sons. Signup and view all the answers

What is a mutation?

A change in the genetic material of an organism. Signup and view all the answers

What is the result of a pathogenic mutation?

A change in the function of the gene product. Signup and view all the answers

What happens when the amino acid sequence of a protein isn't what it should be?

The protein becomes less functional. Signup and view all the answers

What is the difference between a mutation and a pathogenic mutation?

A mutation is a change in the genetic material, while a pathogenic mutation is a disease-causing mutation. Signup and view all the answers

What is an example of Y-linked inheritance?

Hairy eyes Signup and view all the answers

What is the consequence of a pathogenic mutation?

A disease phenotype or clinical manifestation. Signup and view all the answers

Not all mutations are pathogenic because...

some mutations do not affect the gene product function. Signup and view all the answers

What type of mutation involves the removal of a nucleotide from a DNA sequence?

Deletion Signup and view all the answers

Where can mutations that affect gene expression be found?

Non-coding DNA Signup and view all the answers

What is the direct result of a deletion mutation in a DNA sequence?

A nucleotide is removed from the sequence Signup and view all the answers

What is the effect of a mutation in a non-coding DNA region on the encoded protein?

It affects mRNA processing and translation Signup and view all the answers

What type of mutation involves the addition of a nucleotide to a DNA sequence?

Insertion Signup and view all the answers

Where can mutations that directly impact the amino acid sequence of a protein be found?

Coding DNA Signup and view all the answers

What is the effect of a mutation in a coding DNA region on the encoded protein?

It directly impacts the amino acid sequence Signup and view all the answers

What can be the result of a mutation in a regulatory region of DNA?

A change in gene expression Signup and view all the answers

Study Notes

Autosomal Dominant Inheritance

100% penetrance, but may have reduced penetrance (~75%) or incomplete penetrance
Features:
- Variable Expressivity: variation in severity/symptoms of disorder between individuals with the same mutation
- New mutation rate: de novo mutation rate varies considerably between AD conditions
- Somatic mosaicism: new mutation arising at early stage in embryogenesis, present in only some tissues/cells
- Germ-line mosaicism (gonadal mosaicism): new mutation arises during oogenesis or spermatogenesis
- Anticipation: worsening of disease severity in successive generations, characteristically occurs in triplet repeat disorders like Huntington's

Autosomal Recessive Inheritance

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, with both parents being carriers
May be consanguinity
Hardy-Weinberg equation: p²+ 2pq+ q² = 1 used to estimate the frequency of the carrier state (2pq) for an autosomal recessive trait

X-Linked Inheritance

Women have two X chromosomes, can be homozygous or heterozygous
Men have one X and a Y, hemizygous
X-linked inheritance can be:
- Recessive: women are carriers + unaffected, no male to male transmission
- Dominant: women are affected, males more severely affected/lethal
X-linked genes 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

X-Linked Recessive Inheritance

Aspects:
- Skewed X-inactivation: normally the majority of genes on one of a woman's X-chromosomes are inactivated
- Manifesting carriers: some women have some symptoms in X-linked recessive conditions

Y-Linked Inheritance

Always and only passed from fathers to sons

Mutations

A change in the genetic material
A pathogenic mutation (pathogenic variant) results in an alteration of the function of the gene product and can cause a disease phenotype
Types of mutations:
- Deletions: removal of a nucleotide from the DNA sequence
- Insertions: addition of an extra nucleotide to the DNA sequence
Mutations can be found in:
- Coding DNA
- Non-coding DNA (such as promoters and introns)

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Test your knowledge about Huntington's disease, its causes, symptoms, and diagnosis. Take this quiz to learn more about this genetic disorder.

Huntington's Disease Quiz

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Questions and Answers

What is the chance of children of a carrier female inheriting the mutant allele?

What is the typical outcome of X-inactivation in a woman's X-chromosomes?

What is the term for the phenomenon where some women have some symptoms in X-linked recessive conditions?

What percentage of women have uneven or skewed X-inactivation?

What is the consequence of skewed X-inactivation in some women?

What is the term for the daughters of affected males who are carriers of the mutant allele?

What is the Hardy-Weinberg equation used to estimate?

What is the genotype of a male with respect to X-linked genes?

What is a characteristic of X-linked recessive inheritance?

What is the reason for X-inactivation?

What is a characteristic of Autosomal Dominant Inheritance?

What is unique about X-linked genes?

What is the term for the worsening of disease severity in successive generations?

When does Germ-line mosaicism occur?

What is the effect of X-inactivation on one of the X-chromosomes?

What is the result of a female being a carrier of an X-linked recessive trait?

What is the term for new mutations arising at an early stage in embryogenesis?

What is the difference between a female and a male with respect to X-linked genes?

What is the probability of an individual manifesting a disease with Autosomal Dominant Inheritance if they have a mutated gene?

What is the characteristic of Autosomal Recessive Inheritance?

What is the probability of an individual being a carrier of an Autosomal Recessive disease if they have one mutated gene?

What is the characteristic of Autosomal Dominant Inheritance that results in an earlier age of onset?

What is the term for the variation in severity or symptoms of a disorder between individuals with the same mutation?

What is the characteristic of Autosomal Recessive Inheritance that results in consanguinity?

What is the characteristic of Y-linked inheritance?

What is a mutation?

What is the result of a pathogenic mutation?

What happens when the amino acid sequence of a protein isn't what it should be?

What is the difference between a mutation and a pathogenic mutation?

What is an example of Y-linked inheritance?

What is the consequence of a pathogenic mutation?

Not all mutations are pathogenic because...

What type of mutation involves the removal of a nucleotide from a DNA sequence?

Where can mutations that affect gene expression be found?

What is the direct result of a deletion mutation in a DNA sequence?

What is the effect of a mutation in a non-coding DNA region on the encoded protein?

What type of mutation involves the addition of a nucleotide to a DNA sequence?

Where can mutations that directly impact the amino acid sequence of a protein be found?

What is the effect of a mutation in a coding DNA region on the encoded protein?

What can be the result of a mutation in a regulatory region of DNA?

Study Notes

Autosomal Dominant Inheritance

Autosomal Recessive Inheritance

X-Linked Inheritance

X-Linked Recessive Inheritance

Y-Linked Inheritance

Mutations

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