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Questions and Answers
What phenotype is expressed when gene W has any dominant alleles?
What phenotype is expressed when gene W has any dominant alleles?
In the context of the summer squash, what does dominant epistasis indicate?
In the context of the summer squash, what does dominant epistasis indicate?
What is the genotype of black cats in the all-white cat crossing?
What is the genotype of black cats in the all-white cat crossing?
What phenotypic ratio results from crossing the all-white cats?
What phenotypic ratio results from crossing the all-white cats?
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What molecular basis is responsible for the blue color in harebell flowers?
What molecular basis is responsible for the blue color in harebell flowers?
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Which of the following statements about complementation is true?
Which of the following statements about complementation is true?
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In a complementation test, which outcome indicates that mutations are allelic?
In a complementation test, which outcome indicates that mutations are allelic?
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Which genotype combination leads to the all-white phenotype in the cats?
Which genotype combination leads to the all-white phenotype in the cats?
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Which of the following correctly describes the relationship between genes and phenotypes?
Which of the following correctly describes the relationship between genes and phenotypes?
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What role do regulatory genes play in gene interactions?
What role do regulatory genes play in gene interactions?
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What is meant by the term 'molecular machines' in the context of gene interactions?
What is meant by the term 'molecular machines' in the context of gene interactions?
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How can proteins encoded by one gene influence the function of another gene's protein?
How can proteins encoded by one gene influence the function of another gene's protein?
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In what way can the environment affect gene interactions?
In what way can the environment affect gene interactions?
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Which statement regarding the influence of alleles on phenotypes is correct?
Which statement regarding the influence of alleles on phenotypes is correct?
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What is the role of proteins encoded by one gene in relation to another gene?
What is the role of proteins encoded by one gene in relation to another gene?
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Why is it misleading to view alleles as solely determining phenotypes?
Why is it misleading to view alleles as solely determining phenotypes?
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What genotype leads to a black coat color in Labrador retrievers?
What genotype leads to a black coat color in Labrador retrievers?
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Which genotype represents a brown Labrador retriever?
Which genotype represents a brown Labrador retriever?
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In the context of recessive epistasis, what does the genotype 'ee' indicate for coat color deposition in Labrador retrievers?
In the context of recessive epistasis, what does the genotype 'ee' indicate for coat color deposition in Labrador retrievers?
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When crossing a true-breeding white summer squash plant with a true-breeding green plant, what color will the F1 progeny display?
When crossing a true-breeding white summer squash plant with a true-breeding green plant, what color will the F1 progeny display?
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What is the ratio of yellow to white to green in the F2 generation after self-crossing the F1 white squash plants?
What is the ratio of yellow to white to green in the F2 generation after self-crossing the F1 white squash plants?
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What role does the 'B' allele play in determining coat color in Labrador retrievers?
What role does the 'B' allele play in determining coat color in Labrador retrievers?
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Which of the following genotypes would lead to a yellow coat color in Labrador retrievers?
Which of the following genotypes would lead to a yellow coat color in Labrador retrievers?
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In dominant epistasis affecting the summer squash fruit color, what do the genotypes WWYY and WwYy both result in?
In dominant epistasis affecting the summer squash fruit color, what do the genotypes WWYY and WwYy both result in?
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What is the result when two mutations in different genes complement each other?
What is the result when two mutations in different genes complement each other?
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What is the consequence of a homozygous mutation in an individual gene?
What is the consequence of a homozygous mutation in an individual gene?
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In the context of gene interaction, what does a 9:7 F2 ratio indicate?
In the context of gene interaction, what does a 9:7 F2 ratio indicate?
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What term describes the chain of events triggered by an environmental signal in an organism?
What term describes the chain of events triggered by an environmental signal in an organism?
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What results from a cross between two yellow mice when a lethal allele is involved?
What results from a cross between two yellow mice when a lethal allele is involved?
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What role do specific enzymes encoded by genes play in pigment production?
What role do specific enzymes encoded by genes play in pigment production?
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In the context of gene interaction, what occurs when products of genes at different loci combine to create new phenotypes?
In the context of gene interaction, what occurs when products of genes at different loci combine to create new phenotypes?
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What would be the prediction when crossing mutants $ and ¥?
What would be the prediction when crossing mutants $ and ¥?
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How is the accumulation of a precursor due to mutations described?
How is the accumulation of a precursor due to mutations described?
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What is the role of an epistatic gene in epistasis?
What is the role of an epistatic gene in epistasis?
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What does intercrossing of mutants lead to in terms of gene interaction?
What does intercrossing of mutants lead to in terms of gene interaction?
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Which description best fits recessive epistasis?
Which description best fits recessive epistasis?
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What color expression in Labrador retrievers is controlled by one gene affecting hair color and another affecting color deposition?
What color expression in Labrador retrievers is controlled by one gene affecting hair color and another affecting color deposition?
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What is likely true for plants that are genetically identical but have different pigmentation?
What is likely true for plants that are genetically identical but have different pigmentation?
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What is the effect of gene interaction on the expected phenotypic ratios?
What is the effect of gene interaction on the expected phenotypic ratios?
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In the context of two separate genes controlling feather color in Budgerigar parakeets, how do these genes interact?
In the context of two separate genes controlling feather color in Budgerigar parakeets, how do these genes interact?
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What is the role of a regulatory gene in gene expression?
What is the role of a regulatory gene in gene expression?
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What is the phenotypic ratio observed in the F2 generation when a dihybrid F1 plant is selfed?
What is the phenotypic ratio observed in the F2 generation when a dihybrid F1 plant is selfed?
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What is an example of a suppressor gene effect?
What is an example of a suppressor gene effect?
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In a dihybrid cross involving regulatory and structural genes, which alleles are necessary for a functional structural protein to be synthesized?
In a dihybrid cross involving regulatory and structural genes, which alleles are necessary for a functional structural protein to be synthesized?
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What phenotype does the genotype pd/pd; su/su express?
What phenotype does the genotype pd/pd; su/su express?
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What happens when both regulatory and target genes are mutant?
What happens when both regulatory and target genes are mutant?
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Which of the following statements about suppressor genes is true?
Which of the following statements about suppressor genes is true?
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In a cross between r/r and a/a lines, what is produced in the F1 generation?
In a cross between r/r and a/a lines, what is produced in the F1 generation?
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Study Notes
Lecture 10: Gene and Environment Interactions
- Genetics success often comes from correlating phenotypes and alleles.
- Initially, alleles were often viewed as sole determinants of phenotypes, but this oversimplifies the relationship between genes and phenotypes.
- Genes cannot act independently; they must work together with other genes and the environment.
- A gene's influence on a phenotype requires interaction with many other genes and environmental factors (internal and external).
- The lecture examines the various ways these interactions occur.
10.1 Introduction
- Early genetic success relied on correlating traits (e.g., yellow vs. green peas) with alleles.
- However, it's crucial to recognize that genes don't act in isolation.
- Genes work together (and with the environment) to produce phenotypes.
- A gene alone—a DNA segment in a test tube—can't do anything meaningful.
10.2 Genes and Environment
- Figure 6-1 shows how genes and environmental factors interact:
- Environmental signals (e.g., light, chemicals) directly influence a gene.
- Environmental supply (e.g., nutrients) impacts gene action.
- Genes for protein modification and regulatory proteins interact with the gene of interest.
- Genes involved in binding proteins also influence the process.
10.2 Gene Interaction that Produces New Phenotypes
- Gene interactions arise when gene products at different loci combine to form novel phenotypes not predictable from individual loci.
- A classic example is pepper color in plants because two separate genes (Y & C) affect the single trait of pepper color and each is independent from the other.
10.3 Gene Interaction with Epistasis
- Epistasis occurs when a gene's genotype influences the expression of another gene.
- This masking effect (one gene masking another) happens at different loci.
- Epistasis leads to new phenotypes not fully explained by single-gene effects.
- Epistatic genes can behave recessively or dominantly.
10.3.1 Recessive Epistasis
- Recessive epistasis involves epistatic genes acting in a recessive manner.
- An example is coat color in Labrador retrievers.
- Two genes determine color: one for black/brown and another determining the deposit of color in the hair/fur.
- The combination of alleles results in different coat colors via gene interaction.
10.3.2 Dominant Epistasis
- Dominant epistasis describes when an epistatic gene behaves in a dominant manner.
- A classic example is color in summer squash, a plant trait influenced by two genes. One gene controls the production of a substrate/enzyme which determines the color. The other gene encodes the enzyme that converts into a final color.
- The F1 generation exhibits a different phenotype ratio from that predicted by simple independent loci.
10.3 Gene Interaction with Complementation
- Complementation is the generation of a wild-type phenotype when two haploid genomes with separate recessive mutations unite in the same cell.
- A complementation test uses homozygous parents with different mutations to determine if mutations are at the same locus.
- If mutations are at different loci, the combined result is a wild-type phenotype. This is a result of the interaction of two genes (i.e., those with different loci).
- An example is anthocyanin production in harebells to generate a blue color from a biochemical pathway involving non-pigments.
10.4 Regulatory Genes
- Regulatory genes control another gene's expression level via interaction with enzymes/proteins, etc.
- Genes can regulate/modify other genes or gene products
- An example is affecting gene transcription by binding to an upstream regulatory site, allowing RNA polymerase access.
10.4 Suppressor Genes
- Suppressors are a particular type of gene interaction where a mutant allele of one gene reverses a mutation in another gene.
- The key distinction between suppression and epistasis is that suppression often results in a wild-type phenotype (or a phenotype that's similar). While epistasis often generates different phenotypic ratios (9:3:4 or 12:3:1 ratios, etc.)
Table 4.4: Modified Dihybrid Phenotypic Ratios
- A table presenting different ratios for genotypic combinations and the types of interactions observed relating to these combinations.
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Description
This lecture explores the intricate relationship between genes and the environment, highlighting how alleles and multiple genes work together to influence phenotypes. It emphasizes that genes do not act in isolation but require environmental interactions for meaningful expression. Various examples illustrate these interactions and their implications in genetics.
