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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.
- Fall '14