Why Are the Progeny of a Testcross Generally Used to Map

question 4

Multiple Choice

Why are the progeny of a testcross generally used to map loci? Why not the F₂ progeny from an F₁ × F₁ cross?

• A) Only recombinant offspring would be found in the progeny of an F₁ × F₁ cross.
• B) The progeny of an F₁ × F₁ cross would be found in a 9:3:3:1 ratio when two genes are involved, whereas the progeny of a testcross would result in a 1:1:1:1 ratio.
• C) It is easier to classify recombinant and parental offspring of a testcross than with the progeny of an F₁ × F₁ cross.
• D) In a testcross more of the progeny would be expected to display the dominant phenotype than in the progeny of an F₁ × F₁ cross.
• E) A testcross is more useful for mapping genes that are located near each other but, when genes are quite far apart on the same chromosome, an F₁ × F₁ cross actually is more useful.

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Definitions:

Flatworm

A group of simple, soft-bodied invertebrates that belong to the phylum Platyhelminthes, characterized by their flattened bodies and lack of specialized respiratory and circulatory systems.

Ammonia

A compound of nitrogen and hydrogen (NH3) that is a byproduct of the metabolism of animals and is used in various industrial processes.

Metanephridial Organs

Metanephridial organs are excretory structures in some invertebrates, including annelids, that filter fluid directly from the animal's body cavity.

Mollusks

Invertebrates with a soft body, often protected by a hard shell, belonging to the phylum Mollusca, which includes snails, clams, and squids.