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Questions and Answers
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?
- Haplotype, because it represents a common genetic variant in a population.
- Recessive allele, assuming it does not cause a dominant phenotype.
- Wild-type allele, because it is the most common in the population. (correct)
- Mutant allele, due to its deviation from the ancestral sequence.
Which of the following scenarios best illustrates allelic heterogeneity?
Which of the following scenarios best illustrates allelic heterogeneity?
- Mutations in the LDLR, PCSK9, and APOB genes all resulting in familial hypercholesterolemia.
- A single mutation in the PAH gene causing a complete loss of phenylalanine hydroxylase activity.
- A mutation in the CFTR gene causing cystic fibrosis, while a mutation in a separate gene causes similar lung dysfunction.
- Over 100 different mutations within the PAH gene each capable of causing phenylketonuria. (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?
- Allelic heterogeneity
- Locus heterogeneity (correct)
- Haplotype insufficiency
- Compound heterozygosity
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?
If a mother with a heterozygous genotype for an X-linked gene (one mutant allele, one wild-type allele) has children with a father who has the wild-type allele on his X chromosome, what is the probability that their son will express the mutant phenotype?
If a mother with a heterozygous genotype for an X-linked gene (one mutant allele, one wild-type allele) has children with a father who has the wild-type allele on his X chromosome, what is the probability that their son will express the mutant phenotype?
In a scenario where multiple alleles exist for a single gene within a population, which of the following statements accurately describes the relationship between these alleles and the resulting phenotypes?
In a scenario where multiple alleles exist for a single gene within a population, which of the following statements accurately describes the relationship between these alleles and the resulting phenotypes?
Which of the following best describes the difference between a gene and an allele?
Which of the following best describes the difference between a gene and an allele?
How does the concept of a haplotype contribute to our understanding of genetic inheritance and disease mapping?
How does the concept of a haplotype contribute to our understanding of genetic inheritance and disease mapping?
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 of a gene at a specific location (locus) on a chromosome. It's a different version of the same gene.
Haploid
Haploid
Having only one set of chromosomes (n), as in gametes (sperm and ova).
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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Allelic Heterogeneity
Allelic Heterogeneity
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Study Notes
Key Genetics Terminology
- The official definition of a gene is a distinct sequence of nucleotides forming part of a chromosome, the order of which determines the order of monomers in a polypeptide or nucleic acid molecule that a cell or a virus may synthesize.
- Genes can transcribe into non-coding RNAs like microRNAs (miRNAs), long non-coding RNAs (lncRNAs), ribosomal RNAs (rRNAs) and transfer RNAs (tRNAs).
- In humans, a gene is a single DNA region that can be transcribed into RNA and may be translated into a protein.
- An allele refers to one copy of DNA that covers a gene.
- The term allele is only used when more than one variant of a gene exists in a population.
- Blood type alleles A, B, and O are examples.
- The most common allele found in a population is referred to as the Wild-type allele.
- Any variant of the gene that differs from the wild-type is called a Mutant allele.
- "Mutant" does not always mean disease-causing.
- Some alleles, like those for blood type, are all considered wild-type because they are common and not harmful.
- A cell with only one set of chromosomes is called Haploid (n).
- Gametes (sperm and ova) are haploid and carry one copy of each chromosome.
- A cell with two sets of chromosomes is called Diploid (2n).
- Almost all cells in the human body are diploid and carry two copies of each chromosome (one from each parent).
- When a sperm (haploid) fertilizes an ovum (haploid), they form a zygote (diploid).
- A haplotype is a set of genetic variants that are inherited together because they are physically close on the chromosome and rarely separated by recombination.
- A hypothetical genetic sequence with three common variants: TGC and CAT, is a haplotype example.
- Because these variants are close together, they are usually inherited as a single unit.
- A Diplotype is a combination of two haplotypes that an individual inherits.
- A person who has two identical haplotypes has the diplotype TGC/TGC.
- A person who has two different haplotypes has the diplotype TGC/CAT.
- Homozygous means an individual inherits two identical alleles for a given gene.
- CC (homozygous C) and DD (homozygous D) are examples of homozygous.
- Heterozygous means an individual inherits two different alleles for a given gene.
- CD (heterozygous C and D) are examples of heterozygous
- In most genes, it does not matter whether the maternal allele or paternal allele is inherited.
- A male inherits only one copy of a gene on the X chromosome because males have one X and one Y chromosome.
- Hemizygous refers to having only one copy of a gene instead of the usual two.
- Daughters inherit an X from both parents and some daughters will be homozygous (blue/blue), while others will be heterozygous (blue/red).
- Sons inherit an X from their mother and a Y from their father with some sons will be hemizygous (blue), while others will be hemizygous (red).
- Allelic heterogeneity: Different mutations in the same gene can cause the same disease.
- Phenylketonuria (PKU) is caused by mutations in the PAH gene (over 100 different variants exist).
- Cystic Fibrosis (CF) is caused by mutations in the CFTR gene (many different variants exist).
- Locus Heterogeneity: Mutations in different genes can cause the same disease.
- Familial Hypercholesterolemia can be caused by mutations in LDLR, PCSK9, or APOB genes.
- Retinitis Pigmentosa can be caused by mutations in over 50 different genes.
- Compound Heterozygosity occurs when an individual has two different disease-causing variants in the same gene.
- Consanguinity and recessive diseases involves when parents are related, their child is more likely to inherit two identical disease-causing mutations (homozygous).
- When parents are not related, the child is more likely to inherit two different disease-causing mutations (compound heterozygosity).
Key Genetics Concepts
- Wild-type allele is typically defined as the most common allele in a population.
- The definition can be context-dependent and may not always imply functional superiority or ancestral origin.
- Allelic heterogeneity refers to the phenomenon where multiple different mutations within the same gene locus cause the same or similar phenotype.
- Locus heterogeneity occurs when mutations in different gene loci can independently cause the same or a very similar phenotype.
- Compound heterozygosity is the state of carrying two different mutant alleles at the same gene locus, one on each chromosome.
- Since the disorder is autosomal recessive, the child must have two non-functional alleles to express the phenotype.
- A haplotype is a set of genetic variants (such as SNPs) located close together on a chromosome that tend to be inherited together.
- The low rate of recombination between them results in their co-inheritance.
- Allelic heterogeneity involves different mutations within the same gene causing the same phenotype, while locus heterogeneity involves different genes causing the same phenotype.
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