Genetics Quiz: Linked Genes and Epistasis
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Questions and Answers

Which of the following is NOT a characteristic of complementary gene action?

  • It is an example of gene interaction where two genes contribute equally to a phenotype.
  • Two genes act independently to produce the same effect. (correct)
  • It results in a 9:7 phenotypic ratio.
  • Genes in the same linear pathway fully complement each other.

What is the expected phenotypic ratio in a dihybrid cross involving two genes showing epistasis with recessive epistasis?

  • 1:5:1
  • 9:3:4 (correct)
  • 1:2:3:1
  • 9:3:3:1

In a test cross involving linked genes, what is the expected outcome if no crossing over occurs?

  • 50% parental, 50% recombinant gametes
  • The phenotypic ratio will be 9:3:3:1.
  • 100% recombinant gametes
  • 100% parental gametes (correct)

Which of the following scenarios would produce 100% recombinant gametes?

<p>Crossing over occurs before DNA duplication. (B)</p> Signup and view all the answers

What is the significance of a decrease in the frequency of recombinant phenotypes in a dihybrid cross?

<p>It suggests that the genes are linked. (C)</p> Signup and view all the answers

Which of the following is a characteristic of coupling phase in linked genes?

<p>Both recessive alleles are on the same chromosome. (B)</p> Signup and view all the answers

Why are multiple crossing over events between linked genes rarely detectable?

<p>Even numbers of crossovers restore parental combinations. (C)</p> Signup and view all the answers

Which of the following statements is TRUE about the effect of linkage on phenotypic ratios?

<p>Linkage can sometimes alter the phenotypic ratio. (A)</p> Signup and view all the answers

What is the primary cause of non-disjunction?

<p>Unequal distribution of chromosomes during cell division (B)</p> Signup and view all the answers

In which of the following organisms is sex determined by the ratio of sex chromosomes to autosomes?

<p>Drosophila (B)</p> Signup and view all the answers

What is the primary role of the SRY gene in human sex determination?

<p>Triggers the development of male reproductive structures (D)</p> Signup and view all the answers

Which of the following statements concerning X-linked recessive disorders is TRUE?

<p>Females are more likely to be carriers, while males are more likely to express the disorder. (C)</p> Signup and view all the answers

What is the main difference between a karyotype and a ploidy?

<p>A karyotype is a visual representation of chromosomes, while ploidy is a numerical description of chromosome sets. (C)</p> Signup and view all the answers

Which of the following statements MOST accurately describes the relationship between non-disjunction and chromosomal inheritance?

<p>Non-disjunction demonstrates the link between chromosome behavior and inheritance. (A)</p> Signup and view all the answers

Which of these options are examples of how gene interactions can lead to changes in expected phenotypic ratios?

<p>Polygenic inheritance (A), Epistasis (D)</p> Signup and view all the answers

Why is it that males are more likely to be affected by X-linked recessive disorders than females?

<p>Males only have one X chromosome, so if it carries the recessive allele, they will express the disorder. (C)</p> Signup and view all the answers

What is the defining characteristic of a suppressor mutation?

<p>It masks the effects of another mutation. (C)</p> Signup and view all the answers

A dihybrid cross is expected to have a phenotypic ratio of 9:3:3:1. How many degrees of freedom would this cross have in a Chi-Square test?

<p>3 (A)</p> Signup and view all the answers

How can pathway analysis be used to identify allelic mutations?

<p>By observing the growth responses of mutants when supplemented with different biochemicals. (C)</p> Signup and view all the answers

If a trait is autosomal recessive, what is the probability that a child will inherit the trait if both parents are carriers?

<p>25% (A)</p> Signup and view all the answers

In the context of sex-linked inheritance, what is the significance of the SRY gene?

<p>It is located on the Y chromosome and determines male sex. (C)</p> Signup and view all the answers

What is the primary purpose of complementation tests?

<p>To determine if two mutations are on the same gene or different genes. (C)</p> Signup and view all the answers

What is the expected phenotypic ratio in the F2 generation of a dihybrid cross involving additive gene action?

<p>9:3:3:1 (D)</p> Signup and view all the answers

Which of the following statements correctly describes pleiotropy?

<p>A single gene can influence multiple, unrelated phenotypic traits. (B)</p> Signup and view all the answers

What is the defining characteristic of a synthetic lethal mutation?

<p>Two mutations combined lead to cell death, but each individual mutation is viable. (B)</p> Signup and view all the answers

Why does polygenic inheritance lead to continuous variation in phenotypes?

<p>The effects of multiple genes are additive. (D)</p> Signup and view all the answers

What is the primary purpose of a test cross?

<p>To determine the genotype of an organism with a dominant phenotype. (A)</p> Signup and view all the answers

Which of the following is NOT a basic probability rule used in Mendelian genetics?

<p>Subtractive rule (B)</p> Signup and view all the answers

Which of the following is an example of a monohybrid cross?

<p>Crossing two pea plants, one with yellow seeds and the other with green seeds. (B)</p> Signup and view all the answers

How is the first law of Mendelian genetics demonstrated?

<p>Through the observation of the distribution of alleles in the F1 generation of a monohybrid cross. (D)</p> Signup and view all the answers

What is the key difference between recombinant phenotypes and parental phenotypes in F2 progeny?

<p>Recombinant phenotypes are a result of new combinations of alleles formed through genetic recombination, while parental phenotypes are a result of the same combinations of alleles present in the original parents. (D)</p> Signup and view all the answers

Which of the following statements accurately describes the multiplicative rule of probability in genetics?

<p>It helps calculate combined probabilities of two events occurring simultaneously. (A)</p> Signup and view all the answers

How is the second law of Mendelian genetics evident?

<p>Through the observation of different combinations of traits in F2 progeny resulting from dihybrid crosses. (C)</p> Signup and view all the answers

What is the significance of the independent assortment of alleles in dihybrid crosses?

<p>It leads to increased phenotypic variation in F2 generation. (B)</p> Signup and view all the answers

What is the recombination frequency (RF) in a test cross where 400 progeny exhibit the dominant phenotype and 100 exhibit the recessive phenotype?

<p>0.2 (C)</p> Signup and view all the answers

What is the primary difference between a physical map and a genetic map?

<p>A physical map is based on physical distances measured in base pairs, while a genetic map is based on recombination frequencies. (B)</p> Signup and view all the answers

What is meant by the statement that 'the RF begins to underestimate the map distance'?

<p>The RF is not a reliable measure of genetic distance when the genes are very far apart. (A)</p> Signup and view all the answers

What is the relationship between map distance and recombination frequency according to the content provided?

<p>They have a direct correlation, but only up to a certain point. (D)</p> Signup and view all the answers

How is recombination frequency calculated in a test cross?

<p>By dividing the number of recombinant progeny by total progeny. (A)</p> Signup and view all the answers

Why is a test cross used to determine recombination frequency?

<p>Because it provides a direct measure of the number of recombinant gametes produced by the hybrid parent. (B)</p> Signup and view all the answers

Why is a two-point cross used in building genetic maps?

<p>To determine the relative positions of genes on a chromosome. (C)</p> Signup and view all the answers

What is the primary limitation of genetic mapping?

<p>It cannot be used to map genes that are very close together. (B)</p> Signup and view all the answers

Flashcards

Monohybrid Cross

A cross between two organisms differing in one character, showcasing a single trait's inheritance.

Dihybrid Cross

A cross between organisms differing in two characters, helps understand segregation of traits.

Test Cross

Crossing a dominant phenotype organism with a recessive to determine the dominant's genotype.

Multiplicative Rule

Calculates probability of two independent events occurring together: P(A and B) = P(A) x P(B).

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Additive Rule

Calculates probability of either of two mutually exclusive events: P(A or B) = P(A) + P(B).

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First Law of Mendelian Genetics

States dominance and segregation of alleles; shows predictive probabilities in genetic crosses.

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Second Law of Mendelian Genetics

Describes independent assortment of alleles in dihybrid crosses, leading to genetic variation.

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Recombinant Phenotypes

Phenotypes that arise from the recombination of alleles, distinct from parental types.

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Parental phenotypes

Traits that resemble the combination of parental genes in offspring.

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Second law of inheritance

States that alleles of multiple genes segregate independently during gamete formation.

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Chi-Square Test

A statistical method to determine if observed data fit expected Mendelian ratios.

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Degrees of freedom

Calculated as the number of phenotypic classes minus one.

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Observed vs Expected

In chi-square, 'O' is observed values and 'E' are expected values of traits.

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Autosomal dominant

A pattern where at least one affected parent results in the phenotype appearing in every generation.

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Autosomal recessive

A pattern that can have unaffected parents and may skip generations.

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X-linked inheritance

Traits passed through genes located on the X chromosome, often affecting males more than females.

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Non-disjunction

Failure of chromosomes to separate properly during cell division, leading to abnormal chromosome numbers.

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Sex as a phenotype

An observable characteristic determined by an individual's genetic makeup, specifically related to sex.

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Drosophila sex determination

In fruit flies, sex is determined by the ratio of sex chromosomes (X) to autosomes; males are XY and females are XX.

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Human sex determination

In humans, sex is determined by the presence of certain chromosomes; males are XY, and females are XX.

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X-linked recessive

A disorder where males are more frequently affected due to having only one X chromosome that can carry a recessive allele.

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Karyotype

A visual representation of an organism's complete set of chromosomes, detailing their number, size, and shape.

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Ploidy

The number of sets of chromosomes within a cell, indicating whether it is haploid or diploid.

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Complementary Gene Action

Interaction where genes in a linear pathway fully cooperate, resulting in a 9:7 ratio.

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Duplication Gene Action

Occurs when two dominant genes perform the same step in a pathway, leading to a 1:5:1 ratio.

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Epistasis

Gene interaction that modifies phenotypic ratios, leading to changes like 9:3:4.

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Linkage

When linked genes show reduced recombination, leading to more parental phenotypes than expected.

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Coupling Phase

Gene arrangement where both recessive alleles are inherited from one parent.

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Repulsion Phase

Gene arrangement with one recessive allele from each parent, combining from different sources.

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Crossing Over

Process during meiosis that exchanges genetic material between homologous chromosomes, leading to recombinant gametes.

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Maximum Recombinant Percentage

The highest percentage of recombinant types possible, capped at 50% during crossing over.

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Pleiotropy

Single gene influences multiple, unrelated traits.

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Polygenic Inheritance

Many genes contribute to a single trait, leading to variations.

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Completion Tests

Determines the number of genes affecting a trait.

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Pathway Analysis

Organizes genes based on growth responses and biochemical interactions.

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Suppressor Mutation

Mutation that suppresses the effects of another mutation.

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Enhancer Mutation

Mutation that enhances the effects of another mutation.

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Synthetic Lethal Mutations

Combination of two mutations causes cell death, despite each being viable alone.

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Additive Gene Action

Independent genes influence the same phenotype, leading to specific ratios.

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Recombination Frequency (RF)

The ratio of total recombinant phenotypes to total progeny produced from a genetic cross.

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F2 Progeny

Offspring from crossing two F1 individuals; reveals recombinant gametes frequency.

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Map Distance

The genetic distance between two loci, expressed in centimorgans or map units.

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Genetic Map

A representation of relative gene positions based on recombination frequencies; also called linkage map.

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Physical Map

Displays the actual positions of genes based on base pairs or kilobases; influenced by recombination rates.

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Crossover Frequency

The average number of crossovers occurring between two points on a chromosome, influencing genetic map distance.

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Two-Point Crosses

Genetic techniques used to determine recombination frequencies between pairs of genes.

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Study Notes

Topic 1 - Fundamental Principles of Inheritance

  • Mendel's controlled crosses investigated inheritance patterns. Monohybrid crosses examined single traits, while dihybrid crosses examined two traits, revealing independent assortment.
  • Test crosses involved crossing an organism with a dominant trait with one having a recessive trait to determine the genotype of the organism with the dominant trait. This helps distinguish between homozygous dominant and heterozygous dominant genotypes.
  • Basic Probability Rules are essential for calculating probabilities of events happening together or separately.
    • Multiplicative Rule: calculates the probability of two independent events occurring together by multiplying their individual probabilities. (P(A and B) = P(A) x P(B))
    • Additive Rule: calculates the probability of either one or the other of two mutually exclusive events occurring by summing their individual probabilities and subtracting the probability of both occurring together. (P(A or B) = P(A) + P(B) - P(A and B))

First Law of Mendelian Genetics

  • Evidence of Dominance: One allele (dominant) overshadows another (recessive). Observed in monohybrid crosses.
  • Segregation of Alleles: Each individual has two alleles for every gene, that segregate during gamete formation, maintaining genetic variation and influencing inheritance patterns.
  • Predictions of Probabilities in Crosses: Genetic predictions are based on probabilities to ensure accurate predictions of genotypes and phenotypes in offspring.

Second Law of Mendelian Genetics

  • Evidence of Assortment: Alleles of different genes segregate independently. This was discovered in dihybrid crosses, resulting in different allele combinations.
  • Identification of Recombinant/Parental Phenotypes: This helps differentiate new combinations (recombinants) from parental combinations, allowing insights into inheritance patterns.

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Description

Test your understanding of the intricate concepts of complementary gene action, dihybrid crosses, and linkage in genetics. This quiz will challenge you with questions about recombinant gametes and the significance of epistasis. Dive deeper into the fascinating world of genetics and learn about the factors affecting phenotypic ratios.

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