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Ch. 3 - Mendelian Genetics
Klug - Concepts of Genetics  12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
Chapter 3, Problem 9

Which of Mendel's postulates can only be demonstrated in crosses involving at least two pairs of traits? State the postulate.

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Identify Mendel's four postulates: (1) Unit factors exist in pairs, (2) Dominance and recessiveness, (3) Segregation, and (4) Independent assortment.
Understand that the postulate of independent assortment states that alleles for different traits segregate independently of one another during gamete formation.
Recognize that independent assortment can only be observed when studying two or more pairs of traits, as it involves the behavior of alleles at different loci.
Consider a dihybrid cross (e.g., AaBb x AaBb) to demonstrate independent assortment, where the alleles for one trait (A/a) segregate independently of the alleles for another trait (B/b).
Conclude that Mendel's postulate of independent assortment is the one that requires crosses involving at least two pairs of traits to be demonstrated.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Mendel's Law of Independent Assortment

Mendel's Law of Independent Assortment states that alleles for different traits segregate independently of one another during gamete formation. This principle can only be observed when examining crosses that involve at least two pairs of traits, as it allows for the combination of different alleles to produce various phenotypes in the offspring.
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Mendel's Laws

Dihybrid Cross

A dihybrid cross is a genetic cross that examines the inheritance of two different traits, each represented by two alleles. This type of cross is essential for demonstrating Mendel's Law of Independent Assortment, as it allows researchers to observe how the alleles for each trait assort independently, leading to a variety of possible combinations in the offspring.
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Punnet Square

Phenotypic Ratio

The phenotypic ratio is the ratio of different phenotypes that appear in the offspring from a genetic cross. In a typical dihybrid cross, the expected phenotypic ratio is 9:3:3:1, which illustrates the independent assortment of alleles for two traits. Understanding this ratio is crucial for analyzing the outcomes of crosses involving multiple traits.
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Related Practice
Textbook Question

What advantages were provided by Mendel's choice of the garden pea in his experiments?

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Textbook Question

Mendel crossed peas having round seeds and yellow cotyledons (seed leaves) with peas having wrinkled seeds and green cotyledons. All the F₁ plants had round seeds with yellow cotyledons. Diagram this cross through the F₂ generation, using both the Punnett square and forked-line, or branch diagram, methods.

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Textbook Question
Based on the preceding cross, what is the probability that an organism in the F₂ generation will have round seeds and green cotyledons and be true breeding?
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Textbook Question

In a cross between a black and a white guinea pig, all members of the F₁ generation are black. The F₂ generation is made up of approximately 3/4 black and 1/4 white guinea pigs. Diagram this cross, showing the genotypes and phenotypes.

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Textbook Question

In a cross between a black and a white guinea pig, all members of the F₁ generation are black. The F₂ generation is made up of approximately 3/4 black and 1/4 white guinea pigs. What will the offspring be like if two F₂ white guinea pigs are mated?

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Textbook Question

In a cross between a black and a white guinea pig, all members of the F₁ generation are black. The F₂ generation is made up of approximately 3/4 black and 1/4 white guinea pigs. Two different matings were made between black members of the F₂ generation, with the following results. Diagram each of the crosses.

Cross Offspring

Cross 1 All black

Cross 2 3/4 black, 1/4 white

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