For example as shown in f igure 34a if a tall plant

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Unformatted text preview: ype, but of unknown genotype, is crossed to a known homozygous recessive individual. For example, as shown in F igure 3–4(a) , if a tall plant of genotype DD is testcrossed to a dwarf plant, which must have the dd genotype, all offspring will be tall phenotypically and Dd genotypically. However, as shown in F igure 3–4(b), if a tall plant is Dd and it is crossed to a dwarf plant ( dd ), then one-half of the offspring will be tall ( Dd) and the other half will be dwarf ( dd ). Therefore, a 1:1 tall/dwarf ratio demonstrates the heterozygous nature of the tall plant of unknown genotype. The test cross reinforced Mendel’s conclusion that separate unit factors control traits. Dd dd 1/2 tall Dd • Caratteri legati al Cromosoma Y (rari) all tall 1/2 dwarf FIGURE 3-4 Test cross of a single character. In (a), the tall parent is homozygous, but in (b), the tall parent is heterozygous. The genotype of each tall P1 plant can be determined by examining the offspring when each is crossed to a homozygous recessive dwarf plant. 3.3 Mendel’s Dihybrid Cross Generated a Unique F2 Ratio As a natural extension of the monohybri...
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This document was uploaded on 04/02/2014.

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