Single Gene Disorders Overview

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Questions and Answers

Which statement accurately describes euploidy?

Euploidy occurs exclusively in triploid organisms.

Euploidy results in structural chromosomal abnormalities.

Euploidy refers to any multiple of the haploid number of chromosomes. (correct)

Euploidy leads to a higher incidence of congenital diseases.

Identify the type of mutation that leads to a premature stop codon in protein synthesis.

Point mutation

Gene deletion

Nonsense mutation (correct)

Missense mutation

How can a somatic cell mutation affect an individual?

It can be inherited by the next generation.

It has no impact on the individual.

It may contribute to cancer development. (correct)

It can lead to hereditary diseases.

Which best describes a conservative missense mutation?

It substitutes one amino acid for a biochemically similar one. Signup and view all the answers

Which of the following is NOT a characteristic of Mendelian disorders?

They are exclusively inherited from the parents. Signup and view all the answers

What is the outcome of a deletion in chromosomal mutations?

It causes a total loss of the affected gene. Signup and view all the answers

Which scenario is associated with polyploidy?

A condition leading to spontaneous abortion. Signup and view all the answers

What characterizes an aneuploid condition?

It includes any number of chromosomes that is not a multiple of n. Signup and view all the answers

What is the result of a silent mutation?

It occurs in non-coding regions and does not affect protein function. Signup and view all the answers

Which mutation type would most likely cause a drastic change in the protein produced?

Frame Shift Mutation Signup and view all the answers

Which pattern of inheritance is characterized by a 50% chance for siblings to inherit the trait?

Autosomal Dominant Signup and view all the answers

What is a characteristic of autosomal dominant disorders regarding parental inheritance?

Affected individuals can have unaffected parents due to new mutations. Signup and view all the answers

What is one potential outcome of a mutation in a single gene?

It can lead to multiple phenotypic effects. Signup and view all the answers

Which of the following mutations is characterized by the amplification of a sequence of three nucleotides?

Trinucleotide Repeat Mutation Signup and view all the answers

What does it mean when a disorder exhibits incomplete penetrance?

Some individuals with the mutant gene do not express the phenotype. Signup and view all the answers

Which disorder is associated with the BRCA1 and BRCA2 variants?

Hereditary breast and ovarian cancer Signup and view all the answers

Which statement is true regarding variable expressivity in genetic mutations?

Individuals carrying the same mutant gene can express different symptoms. Signup and view all the answers

What is the primary manifestation of autosomal recessive disorders?

Parents of affected individuals are usually carriers. Signup and view all the answers

What is a characteristic feature of X-linked disorders?

Males are hemizygous, which means they have only one allele for the X-linked gene. Signup and view all the answers

What risk do siblings of an affected individual with an autosomal recessive disorder face?

25% chance of inheriting the disorder. Signup and view all the answers

How does complete penetrance relate to autosomal recessive disorders?

It means that the majority of individuals with the mutation will express the disorder. Signup and view all the answers

What is true about no father-son transmission in X-linked disorders?

Fathers cannot pass the disorder to their sons, but they can to their daughters. Signup and view all the answers

In terms of disease characteristics, what distinguishes late-onset disorders?

Symptoms often manifest in adulthood. Signup and view all the answers

What is a common misconception regarding enzyme-encoding mutations in autosomal recessive disorders?

All autosomal recessive disorders involve mutations in enzyme-encoding genes. Signup and view all the answers

Study Notes

Single Gene Disorders

Genetic Basis: Single-gene disorders, also known as Mendelian or unifactorial disorders, arise from mutations affecting a single gene.
Prevalence: More than 5,000 such disorders are identified, accounting for 1% of adult hospital admissions and 6-8% of pediatric admissions.
Mutation Types: Mutations encompass changes in the DNA sequence, including:
- Chromosome Mutations: Structural alterations (e.g., translocations, deletions) or gain/loss of whole chromosomes (e.g., monosomy, trisomy).
- Gene Mutations: Changes at the level of individual genes, affecting the nucleotide sequence.
  - Germ Cell Mutations: Inherited and cause hereditary diseases.
  - Somatic Cell Mutations: Do not cause hereditary diseases but may lead to cancers or congenital malformations.

Gene Mutations

Point Mutations: Single base substitutions within a DNA sequence:
- Missense Mutation: Replaces one amino acid with another.
  - Conservative: Substituted amino acid is similar to the original, often minimal impact on protein function.
  - Non-Conservative: Substitutes with a biochemically different amino acid, potentially significant consequences for protein function. Example: Sickle cell anemia (mutation in β-globin gene).
- Nonsense Mutation: Converts a codon for an amino acid into a stop codon, leading to premature protein termination. Example: β0-thalassemia (mutation affects glutamine codon, creating a stop codon).
- Silent Mutation: Alters a base pair but does not change the encoded amino acid; often located in non-coding regions and has no impact on protein function.
Frameshift Mutation: Insertion or deletion of nucleotides shifts the reading frame during translation, resulting in a drastically altered protein sequence downstream of the mutation, often leading to non-functional proteins.
Trinucleotide Repeat Mutations: Expansion of a three-nucleotide sequence. Example: Fragile X syndrome (expansion of CGG repeat within the FMR1 gene).

Inheritance Patterns of Single-Gene Disorders

Autosomal Dominant:
- Affected Allele: Manifests with one mutated allele.
- Parent Involvement: Usually, at least one parent is affected.
- Sibling Risk: Siblings have a 50% chance of inheriting the trait.
- New Mutations: Some affected individuals may have unaffected parents due to new mutations.
- Incomplete Penetrance: Individuals may inherit the mutated gene but not exhibit the phenotype.
- Variable Expressivity: The disorder can present differently in individuals carrying the same mutation.
- Late Onset: Symptoms often appear in adulthood.
- Heterozygous Manifestation: The disorder is primarily expressed in heterozygotes.
- Equal Gender Effect: Both males and females are affected equally.
Autosomal Recessive:
- Affected Alleles: Manifests with two mutated alleles.
- Parent Involvement: Parents are typically unaffected carriers.
- Sibling Risk: Siblings have a 25% chance of inheriting the trait.
- Consanguinity: Affected individuals may be the result of consanguineous marriages, especially for rare mutations.
- Uniform Expression: More uniform expression of the disorder compared to dominant disorders.
- Complete Penetrance: High likelihood of individuals with the mutation expressing the disorder.
- Early Onset: Symptoms usually appear early in life.
- Rare New Mutations: New mutations are uncommon.
- Enzyme-Encoding Genes: Many mutated genes in autosomal recessive disorders encode enzymes.
- Inborn Errors of Metabolism: Autosomal recessive disorders include many inborn errors of metabolism.
- X-Linked Disorders:
- No Father-Son Transmission: Fathers cannot transmit the disorder to their sons.
- Obligate Carriers: All daughters of affected males are obligate carriers.
- Hemizygous Males: Males are hemizygous for X-linked genes, meaning they have only one copy.
- Predominantly Recessive: Most X-linked disorders are recessive.
- Sex Distribution: Females are typically carriers, while males are affected.
- Maternal Transmission: Carrier females transmit the disorder to their sons.
- No Paternal Transmission to Sons: Affected males cannot transmit the disease to their sons.
- Rare X-Linked Dominant Disorders: Examples include vitamin D-resistant rickets, Alport's syndrome, Goltz syndrome, and X-linked dominant porphyria.

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Description

Explore the essential aspects of single-gene disorders, including their genetic basis and prevalence in medical settings. This quiz also covers various mutation types, distinguishing between chromosome and gene mutations, as well as the implications of germ cell and somatic cell mutations. Test your knowledge on these important genetic concepts!