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Questions and Answers
A researcher is studying a novel genetic disorder and observes that individuals with the same disease-causing genotype exhibit a wide range of phenotypic severity. Some individuals are mildly affected, while others experience severe complications. Which genetic principle BEST explains this phenomenon?
A researcher is studying a novel genetic disorder and observes that individuals with the same disease-causing genotype exhibit a wide range of phenotypic severity. Some individuals are mildly affected, while others experience severe complications. Which genetic principle BEST explains this phenomenon?
- Incomplete penetrance
- Anticipation
- Variable expressivity (correct)
- Haploinsufficiency
In a species of flowering plant, the allele for red flowers (R) is incompletely dominant to the allele for white flowers (W). Heterozygous individuals (RW) exhibit pink flowers. If two pink-flowered plants are crossed, what proportion of the offspring is EXPECTED to have the same genotype as the parents?
In a species of flowering plant, the allele for red flowers (R) is incompletely dominant to the allele for white flowers (W). Heterozygous individuals (RW) exhibit pink flowers. If two pink-flowered plants are crossed, what proportion of the offspring is EXPECTED to have the same genotype as the parents?
- 50% (correct)
- 25%
- 0%
- 75%
A genetic counselor is advising a couple where both partners are carriers for an autosomal recessive disorder. They express concerns about their future children inheriting only one copy of the disease allele, but not the disease itself. How should the genetic counselor BEST explain the implications of carrier status to the couple?
A genetic counselor is advising a couple where both partners are carriers for an autosomal recessive disorder. They express concerns about their future children inheriting only one copy of the disease allele, but not the disease itself. How should the genetic counselor BEST explain the implications of carrier status to the couple?
- If a child inherits only one copy of the disease allele, they will also be carriers like you, generally without symptoms, but capable of passing the allele to their own children. (correct)
- If a child inherits only one copy of the disease allele from either parent, the normal allele will compensate, preventing them from becoming carriers.
- A single copy of the disease allele guarantees that the child will develop the disease later in life, regardless of the other parent's genetic contribution.
- If a child inherits only one copy of the disease allele, they will exhibit a milder form of the disorder due to incomplete dominance.
In a herd of sheep, the presence of horns is a sex-limited trait. Both males and females can possess the genes for horns, but only males typically express the trait. If a horned male is crossed with a hornless female, what can be concluded about the genotypes of their offspring regarding the horn trait?
In a herd of sheep, the presence of horns is a sex-limited trait. Both males and females can possess the genes for horns, but only males typically express the trait. If a horned male is crossed with a hornless female, what can be concluded about the genotypes of their offspring regarding the horn trait?
A researcher discovers a new genetic mutation that affects multiple, seemingly unrelated organ systems. Individuals with this mutation exhibit symptoms ranging from skeletal abnormalities to cardiovascular defects and vision problems. Which genetic phenomenon BEST explains this wide range of effects from a single mutation?
A researcher discovers a new genetic mutation that affects multiple, seemingly unrelated organ systems. Individuals with this mutation exhibit symptoms ranging from skeletal abnormalities to cardiovascular defects and vision problems. Which genetic phenomenon BEST explains this wide range of effects from a single mutation?
A doctor is evaluating a family with a history of a trinucleotide repeat disorder. They notice that the age of onset for the disease decreases in successive generations. Which genetic mechanism BEST accounts for this observation?
A doctor is evaluating a family with a history of a trinucleotide repeat disorder. They notice that the age of onset for the disease decreases in successive generations. Which genetic mechanism BEST accounts for this observation?
In a particular species of butterfly, wing color is determined by two genes. Gene A controls the base color (A1 for blue, A2 for green), and Gene B influences whether the color is expressed (B1 allows color expression, B2 inhibits color expression). If a butterfly has the genotype A1A2B2B2, what phenotype will it MOST likely exhibit?
In a particular species of butterfly, wing color is determined by two genes. Gene A controls the base color (A1 for blue, A2 for green), and Gene B influences whether the color is expressed (B1 allows color expression, B2 inhibits color expression). If a butterfly has the genotype A1A2B2B2, what phenotype will it MOST likely exhibit?
A genetic study reveals that a particular mutation in a gene causes disease only when a specific modifier gene is also mutated. Individuals with the disease gene mutation alone do not show any symptoms. Which genetic principle BEST explains this observation?
A genetic study reveals that a particular mutation in a gene causes disease only when a specific modifier gene is also mutated. Individuals with the disease gene mutation alone do not show any symptoms. Which genetic principle BEST explains this observation?
A scientist is studying a newly discovered genetic mutation that they suspect is a dominant negative mutation. How can the scientist BEST confirm this hypothesis?
A scientist is studying a newly discovered genetic mutation that they suspect is a dominant negative mutation. How can the scientist BEST confirm this hypothesis?
A research team is investigating a family with a history of a genetic disorder linked to a specific gene. They find that some individuals with the disease-causing genotype do not express the disease phenotype, while others do, and those that do express the disease vary in the severity of the experienced symptoms. Which combination of genetic principles is MOST likely at play?
A research team is investigating a family with a history of a genetic disorder linked to a specific gene. They find that some individuals with the disease-causing genotype do not express the disease phenotype, while others do, and those that do express the disease vary in the severity of the experienced symptoms. Which combination of genetic principles is MOST likely at play?
Flashcards
Dominant Gene
Dominant Gene
Allele that requires only one copy to express its phenotype.
Recessive Gene
Recessive Gene
Allele that requires two copies (homozygous) to express its phenotype.
Co-dominance
Co-dominance
Both alleles are equally expressed in the phenotype.
Haploinsufficiency
Haploinsufficiency
A single functional allele is insufficient for normal function, leading to disease.
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Dominant Negative Disorder
Dominant Negative Disorder
Mutation creates a dysfunctional protein that interferes with the normal protein's function.
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Carrier Status
Carrier Status
Individuals with one normal and one mutated allele for a recessive disease.
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Incomplete Dominance
Incomplete Dominance
Heterozygote shows a blended phenotype, neither allele is fully dominant.
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Penetrance
Penetrance
Proportion of individuals with a genotype that express the associated phenotype.
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Variable Expressivity
Variable Expressivity
Individuals with the same disease genotype show varying severity or symptoms.
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Epistasis
Epistasis
One gene masks the expression of another independently inherited gene.
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Dominant vs. Recessive Genes
- Dominant genes require only one copy to express the associated phenotype.
- Recessive genes require two copies to express the phenotype.
- In Rh factor, the allele for producing the Rh factor (Rh+) is dominant; the allele for not producing it (Rh-) is recessive.
- Genotypes for Rh factor are RH+RH+, RH+RH-, and RH-RH-.
- Phenotypes are Rh positive (RH+) for both homozygous dominant and heterozygous individuals.
- Rh negative (RH-) occurs only in homozygous recessive individuals.
Co-dominance vs. Classic Dominance
- Co-dominance occurs when two alleles are both expressed equally, resulting in a phenotype that shows both traits.
- Blood type AB is co-dominant, with both A and B proteins expressed on the surface of red blood cells.
- Classic dominance is when one allele completely dominates over the other, expressing the dominant allele’s phenotype in heterozygous individuals.
- Blood types A (genotype AO or AA) and B (genotype BO or BB) are examples of classic dominance.
Dominant Inheritance Patterns
- Dominant negative disorders occur when a mutation in one allele causes the gene product to be dysfunctional.
- The presence of one functional allele cannot compensate for the dysfunctional one.
- Huntington's disease is a dominant negative disorder, where the mutated Huntington protein is toxic to nerve cells.
- Mutations in the p53 tumor suppressor gene are also dominant negative, causing cancers.
- Haploinsufficiency occurs when a single functional allele is not enough to maintain normal function.
- Ehlers-Danlos syndrome is an example, where one mutated allele of the collagen gene leads to defective collagen and connective tissue disorders.
Carrier Status
- Carrier status in autosomal recessive diseases involves individuals with one normal allele and one mutated allele.
- Carriers do not express the disease phenotype but can pass on the mutated allele to their offspring.
- Cystic fibrosis is an example, where an individual with genotype Cc does not have cystic fibrosis but can pass the c allele to their children.
Incomplete Dominance
- Incomplete dominance occurs when neither allele is completely dominant.
- The heterozygote shows a blended or intermediate phenotype.
- Snapdragon flowers are an example, where a red flower (RR) crossed with a white flower (WW) results in pink flowers (RW).
- Eye color and hair color in humans can exhibit incomplete dominance.
Penetrance
- Penetrance is the proportion of individuals with a specific genotype that actually express the associated phenotype.
- Complete penetrance is when everyone with the genotype develops the disease phenotype.
- Achondroplasia (dwarfism) has complete penetrance.
- Incomplete penetrance occurs when some individuals with the disease-causing genotype do not express the disease phenotype.
- Hereditary breast cancer (BRCA1 mutation) may not result in cancer for every individual carrying the mutation.
Variable Expressivity
- Variable expressivity occurs when individuals with the same genotype express the same disease, but the severity or symptoms vary.
- Marfan syndrome is an example, where individuals may experience different symptoms, ranging from mild to severe, despite having the same genetic mutation.
Trinucleotide Repeat Disorders
- Trinucleotide repeat disorders are caused by the expansion of a three-nucleotide sequence (e.g., CAG repeats) within a gene.
- Examples include Huntington’s disease (CAG repeats in the HTT gene) and Fragile X syndrome (CGG repeats in the FMR1 gene).
Somatic Instability and Anticipation
- Somatic instability involves the expansion of trinucleotide repeats in somatic cells.
- As individuals with repeat disorders age, their cells may accumulate more repeats, exacerbating the disease.
- Anticipation refers to the phenomenon where offspring of affected individuals experience symptoms of a disease at an earlier age than their parents.
- This is due to the increase in repeat number.
Sex-Influenced and Sex-Limited Traits
- Sex-influenced traits are associated with autosomal genes, but the expression of the trait is influenced by the sex of the individual.
- Male pattern baldness is sex-influenced, with the allele being dominant in males but recessive in females.
- Sex-limited traits are found on autosomes but are expressed only in one sex.
- Horns in sheep are sex-limited, with both male and female sheep carrying the genetic potential, but only males develop them.
Epistasis
- Epistasis occurs when a gene interaction, where one gene can mask the expression of another gene.
- Eye color is influenced by multiple genes.
- The expression of the eye color phenotype depends on the interaction of these genes.
Pleiotropy
- Pleiotropy involves a single gene or variant affecting multiple unrelated traits or systems.
- Marfan syndrome is caused by a mutation in the fibrillin gene.
- This mutation leads to a variety of symptoms, including skeletal deformities, cardiovascular problems, and vision issues.
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