Podcast
Questions and Answers
What is the chance of children of a carrier female inheriting the mutant allele?
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?
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?
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?
What percentage of women have uneven or skewed X-inactivation?
What is the consequence of skewed X-inactivation in some women?
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 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 Hardy-Weinberg equation used to estimate?
What is the genotype of a male with respect to X-linked genes?
What is the genotype of a male with respect to X-linked genes?
What is a characteristic of X-linked recessive inheritance?
What is a characteristic of X-linked recessive inheritance?
What is the reason for X-inactivation?
What is the reason for X-inactivation?
What is a characteristic of Autosomal Dominant Inheritance?
What is a characteristic of Autosomal Dominant Inheritance?
What is unique about X-linked genes?
What is unique about X-linked genes?
What is the term for the worsening of disease severity in successive generations?
What is the term for the worsening of disease severity in successive generations?
When does Germ-line mosaicism occur?
When does Germ-line mosaicism occur?
What is the effect of X-inactivation on one of the X-chromosomes?
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 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 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 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 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 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 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 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 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 Autosomal Recessive Inheritance that results in consanguinity?
What is the characteristic of Y-linked inheritance?
What is the characteristic of Y-linked inheritance?
What is a mutation?
What is a mutation?
What is the result of a pathogenic 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 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 the difference between a mutation and a pathogenic mutation?
What is an example of Y-linked inheritance?
What is an example of Y-linked inheritance?
What is the consequence of a pathogenic mutation?
What is the consequence of a pathogenic mutation?
Not all mutations are pathogenic because...
Not all mutations are pathogenic because...
What type of mutation involves the removal of a nucleotide from a DNA sequence?
What type of mutation involves the removal of a nucleotide from a DNA sequence?
Where can mutations that affect gene expression be found?
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 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 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?
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?
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 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?
What can be the result of a mutation in a regulatory region of DNA?
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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Description
Test your knowledge about Huntington's disease, its causes, symptoms, and diagnosis. Take this quiz to learn more about this genetic disorder.
