Podcast
Questions and Answers
Which of the following scenarios best illustrates allelic heterogeneity?
Which of the following scenarios best illustrates allelic heterogeneity?
- A mutation in the _CFTR_ gene causing cystic fibrosis, while a mutation in a separate gene causes similar lung dysfunction.
- A single mutation in the _PAH_ gene causing a complete loss of phenylalanine hydroxylase activity.
- Mutations in the _LDLR_, _PCSK9_, and _APOB_ genes all resulting in familial hypercholesterolemia.
- Over 100 different mutations within the _PAH_ gene each capable of causing phenylketonuria. (correct)
In a population, a genetic variant is identified that is neither advantageous nor disadvantageous to the organism's survival. Over generations, this variant becomes the most prevalent form of the gene. How would this allele be best characterized according to standard genetic terminology?
In a population, a genetic variant is identified that is neither advantageous nor disadvantageous to the organism's survival. Over generations, this variant becomes the most prevalent form of the gene. How would this allele be best characterized according to standard genetic terminology?
- Recessive allele, assuming it does not cause a dominant phenotype.
- Mutant allele, due to its deviation from the ancestral sequence.
- Haplotype, because it represents a common genetic variant in a population.
- Wild-type allele, because it is the most common in the population. (correct)
Consider a scenario where a researcher is studying a novel genetic disease in humans. Upon analyzing several affected individuals, the researcher discovers that the disease can result from mutations in any one of five different genes, each encoding a protein involved in a common metabolic pathway. Which genetic term best describes this phenomenon?
Consider a scenario where a researcher is studying a novel genetic disease in humans. Upon analyzing several affected individuals, the researcher discovers that the disease can result from mutations in any one of five different genes, each encoding a protein involved in a common metabolic pathway. Which genetic term best describes this phenomenon?
- Locus heterogeneity (correct)
- Compound heterozygosity
- Allelic heterogeneity
- Haplotype insufficiency
A researcher is studying a family with a history of a rare autosomal recessive disorder. Upon genetic testing, an affected child is found to have two different mutations in the disease-causing gene. One mutation was inherited from the mother, and the other from the father. Neither parent exhibits symptoms of the disorder. What is the most likely genetic explanation for the child's condition?
A researcher is studying a family with a history of a rare autosomal recessive disorder. Upon genetic testing, an affected child is found to have two different mutations in the disease-causing gene. One mutation was inherited from the mother, and the other from the father. Neither parent exhibits symptoms of the disorder. What is the most likely genetic explanation for the child's condition?
In a species with a diploid number of 24, what is the expected number of chromosomes present in each gamete following meiosis?
In a species with a diploid number of 24, what is the expected number of chromosomes present in each gamete following meiosis?
A geneticist discovers a new gene in mice. This gene has multiple variants, but one is significantly more common across different wild populations. However, artificial selection in a lab produces new breeds where previously less frequent variants are now dominant. How should the geneticist define the alleles in the wild type population, considering the artificial selection scenario?
A geneticist discovers a new gene in mice. This gene has multiple variants, but one is significantly more common across different wild populations. However, artificial selection in a lab produces new breeds where previously less frequent variants are now dominant. How should the geneticist define the alleles in the wild type population, considering the artificial selection scenario?
If a gene on the X chromosome has two alleles, 'A' and 'a', and a female is heterozygous (Aa), while a male is hemizygous for 'a', what percentage of their male offspring will inherit the 'a' allele?
If a gene on the X chromosome has two alleles, 'A' and 'a', and a female is heterozygous (Aa), while a male is hemizygous for 'a', what percentage of their male offspring will inherit the 'a' allele?
A diplotype consists of:
A diplotype consists of:
Consider a scenario where a common genetic variant is identified in a population. This variant includes three single nucleotide polymorphisms (SNPs) that are located very close to each other on the same chromosome. Statistical analyses reveal that these three SNPs are almost always inherited together, with very few instances of recombination separating them. Which term best describes this set of genetic variants?
Consider a scenario where a common genetic variant is identified in a population. This variant includes three single nucleotide polymorphisms (SNPs) that are located very close to each other on the same chromosome. Statistical analyses reveal that these three SNPs are almost always inherited together, with very few instances of recombination separating them. Which term best describes this set of genetic variants?
Which statement accurately contrasts allelic and locus heterogeneity?
Which statement accurately contrasts allelic and locus heterogeneity?
Flashcards
Gene
Gene
A distinct sequence of nucleotides forming part of a chromosome that determines the order of monomers in a polypeptide or nucleic acid molecule.
Allele
Allele
A variant form of a gene at a specific locus on a chromosome.
Wild-type allele
Wild-type allele
The most common allele in a natural population.
Haploid
Haploid
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Diploid
Diploid
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Haplotype
Haplotype
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Diplotype
Diplotype
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Homozygous
Homozygous
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Heterozygous
Heterozygous
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Hemizygous
Hemizygous
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Study Notes
Key Genetics Terminology
- According to sequence ontology, a gene is a distinct sequence of nucleotides forming part of a chromosome; the order determines the order of monomers in a polypeptide or nucleic acid molecule synthesized by a cell or virus.
- Historically, genes were thought to code for one protein, however it is now known that many genes transcribe into non-coding RNAs.
- Examples of non-coding RNAs include microRNAs (miRNAs), long non-coding RNAs (lncRNAs), ribosomal RNAs (rRNAs), and transfer RNAs (tRNAs).
- In humans, a gene is a specific DNA region that can be transcribed into RNA and may be translated into a protein.
- An allele is a variant of a gene that exists at a specific location (locus) on a chromosome.
- The term allele is used only when more than one variant of a gene exists in a population.
- Example: A, B, and O alleles code for different blood types.
- The wild-type allele is the most common allele found in a natural population.
- A mutant allele is any variant of the gene that differs from the wild-type, though not always disease-causing.
Haploid vs. Diploid
- Haploid (n) is a cell with only one set of chromosomes, such as gametes (sperm and ova) containing one copy of each chromosome.
- Diploid (2n) is a cell with two sets of chromosomes, most human cells are diploid and contain two copies of each chromosome (one from each parent).
- A zygote (diploid) is formed when a sperm (haploid) fertilizes an ovum (haploid).
Haplotype
- A haplotype is a set of genetic variants inherited together due to physical proximity on the chromosome, rarely separated by recombination.
- Example: Hypothetical genetic sequence with three common variants (TGC and CAT); these are usually inherited as a single unit.
Diplotype
- A diplotype is a combination of two haplotypes that an individual inherits.
- Examples: TGC/TGC (two identical haplotypes), TGC/CAT (two different haplotypes), CAT/CAT (another pair of haplotypes).
Homozygous vs. Heterozygous
- Homozygous: An individual inherits two identical alleles for a given gene (e.g., CC, DD).
- Heterozygous: An individual inherits two different alleles for a given gene (e.g., CD).
- Inheritance does not always affect gene function; for most genes, the maternal or paternal allele is irrelevant.
Hemizygous (X-Linked Genes in Males)
- Hemizygous describes males inheriting only one copy of a gene on the X chromosome because males have one X and one Y chromosome
- Example: Father with a blue gene on the X chromosome, mother with one blue and one red gene.
- Some daughters will be homozygous (blue/blue).
- Some daughters will be heterozygous (blue/red).
- Some sons will be hemizygous (blue) or hemizygous (red).
Allelic vs. Locus Heterogeneity
- Allelic heterogeneity is when different mutations in the same gene cause the same disease.
- Example: Phenylketonuria (PKU) is caused by mutations in the PAH gene (over 100 variants).
- Example: Cystic Fibrosis (CF) is caused by mutations in the CFTR gene (many variants).
- Locus heterogeneity is when mutations in different genes cause the same disease.
- Example: Familial Hypercholesterolemia - mutations in LDLR, PCSK9, or APOB genes.
- Example: Retinitis Pigmentosa - mutations in over 50 genes.
Compound Heterozygosity
- Compound heterozygosity occurs when an individual has two different disease-causing variants in the same gene.
- Common in recessive diseases where parents contribute different defective alleles.
- Example: An individual with cystic fibrosis inherits one mutation from the mother and a different mutation from the father in the CFTR gene.
- Consanguinity vs. non-related parents:
- Related parents are more likely to produce offspring homozygous for a disease-causing mutation.
- Non-related parents are more likely to produce offspring with compound heterozygosity.
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