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Inheritance160-page13 - different from either homozygous...

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Inheritance Patterns - 13 Gene Interactions – Beyond Mendel The characteristics that Mendel observed had dominant and recessive forms and each inheritable trait was found on different chromosomes. Early on, some inheritance patterns did not match the expectations proposed by Mendel's principles. We shall now turn our attention to some of the gene interactions that go beyond the basic Mendelian predictions. Single Gene Variations Lack of Dominance Mendel's F 1 offspring always resembled the dominant parent because each of the genes Mendel chose to study showed complete dominance. That is not always the case with genes and their alleles. For many genes there is no dominant allele. Both alleles are expressed when present and the heterozygote will have a phenotype
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Unformatted text preview: different from either homozygous form. This is sometimes referred to as an intermediate phenotype. There are a number of variations in lack of dominance, but each results in heterozygous conditions that have a phenotype different from either homozygous phenotype. In other words, when a gene lacks dominance, there will be three different phenotypes, two homozygous phenotypes (AA and A'A') and a third heterozygous phenotype (AA'). A . Incomplete Dominance • Failure to completely mask or cover the recessive allele • The heterozygote first generation has some intermediate phenotype between the two homozygous forms, often appearing as a blending of the two alleles. • Examples: snapdragon flowers and human hair texture...
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