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Dwarf parent: t Possible gametes: Tt 100% t Dwarf Tt 50% of F,'s are tall Test parent: Tt Possible gametes: tt 50% T 50% t Test parent: TT Possible gametes: 100% T t 100% of F,'s 50% of F,'s are tall are dwarf FIGURE 16-14 Test crosses to determine whether a plant with the dominant phenotype is heterozygous or homozygous. Of the data in this diagram, you would not know the genotypes of the test parents before the test cross; those data are what you are trying to discover. If you want to find only a single homozygote or heterozygote, you would need to do test crosses on only one or a few plants. Imagine, however, that you had done an experimental cross for a trait that you assumed would give you a 3:1 ratio; it would be necessary to do test crosses on a large number of progeny plants with the dominant phenotype just to confirm your experiment.

Dwarf parent: t Possible gametes: Tt 100% t Dwarf Tt 50% of F,'s are tall Test parent: Tt Possible gametes: tt 50% T 50% t Test parent: TT Possible gametes: 100% T t 100% of F,'s 50% of F,'s are tall are dwarf FIGURE 16-14 Test crosses to determine whether a plant with the dominant phenotype is heterozygous or homozygous. Of the data in this diagram, you would not know the genotypes of the test parents before the test cross; those data are what you are trying to discover. If you want to find only a single homozygote or heterozygote, you would need to do test crosses on only one or a few plants. Imagine, however, that you had done an experimental cross for a trait that you assumed would give you a 3:1 ratio; it would be necessary to do test crosses on a large number of progeny plants with the dominant phenotype just to confirm your experiment.

Human Anatomy & Physiology (11th Edition)
Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN:9780134580999
Author:Elaine N. Marieb, Katja N. Hoehn
Publisher:Elaine N. Marieb, Katja N. Hoehn
Chapter1: The Human Body: An Orientation
Section: Chapter Questions
Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...
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When traits show complete dominance, the genotype can be revealed by a test cross. In the example of tall and dwarf plants (Figure) why is it necessary to use the dwarf parent? In general, why is it necessary to use a parent that is homozygous recessive?

Dwarf parent: t Possible gametes: Tt 100% t Dwarf Tt 50% of F,'s are tall Test parent: Tt Possible gametes: tt 50% T 50% t Test parent: TT Possible gametes: 100% T t 100% of F,'s 50% of F,'s are tall are dwarf FIGURE 16-14 Test crosses to determine whether a plant with the dominant phenotype is heterozygous or homozygous. Of the data in this diagram, you would not know the genotypes of the test parents before the test cross; those data are what you are trying to discover. If you want to find only a single homozygote or heterozygote, you would need to do test crosses on only one or a few plants. Imagine, however, that you had done an experimental cross for a trait that you assumed would give you a 3:1 ratio; it would be necessary to do test crosses on a large number of progeny plants with the dominant phenotype just to confirm your experiment.
Transcribed Image Text:Dwarf parent: t Possible gametes: Tt 100% t Dwarf Tt 50% of F,'s are tall Test parent: Tt Possible gametes: tt 50% T 50% t Test parent: TT Possible gametes: 100% T t 100% of F,'s 50% of F,'s are tall are dwarf FIGURE 16-14 Test crosses to determine whether a plant with the dominant phenotype is heterozygous or homozygous. Of the data in this diagram, you would not know the genotypes of the test parents before the test cross; those data are what you are trying to discover. If you want to find only a single homozygote or heterozygote, you would need to do test crosses on only one or a few plants. Imagine, however, that you had done an experimental cross for a trait that you assumed would give you a 3:1 ratio; it would be necessary to do test crosses on a large number of progeny plants with the dominant phenotype just to confirm your experiment.
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