Chapter 3 Extensions to Mendel's Laws
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Sectionsto study3.1Extensions to Mendel for single-gene inheritancePairs of alleles show deviations from complete dominance andrecessiveness.Different forms of the gene are not limited to two alleles.One gene may determine more than one trait.3.2Extensions to Mendel for multifactorialinheritance3-2
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-2 Sections to study Sections to study 3.1 Extensions to Mendel for single 3.1 Extensions to Mendel for single-gene inheritance gene inheritance Pairs of alleles show deviations from complete dominance and Pairs of alleles show deviations from complete dominance and recessiveness recessiveness. Different forms of the gene are not limited to two alleles. Different forms of the gene are not limited to two alleles. One gene may determine more than one trait. One gene may determine more than one trait. 3.2 Extensions to Mendel for 3.2 Extensions to Mendel for multifactorial multifactorial inheritance inheritance
Mendelian pattern of inheritanceSingle-gene traitXYellowpeasGreenpeasTwo alleles(Q:eggs)(:pollen)Clear-cut dominance andrecessivenessAll yellowGenotypic ratio1:2:1Self-fertilizationPhenotypicratio3:16022yellow:2001green3:13-3
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-3 Mendelian Mendelian pattern of inheritance pattern of inheritance Single-gene trait gene trait Two alleles Two alleles Clear-cut dominance and cut dominance and recessiveness recessiveness Genotypic ratio 1: 2: 1 Genotypic ratio 1: 2: 1 Phenotypic ratio 3: 1 Phenotypic ratio 3: 1
Exceptions to Mendelian pattern ofinheritanceSingle-genetraitPairs ofalleles show deviationsfromcomplete dominance andrecessiveness.Differentforms of the gene are not limited totwo alleles.OnegenemaydeterminemorethanonetraitMultifactorialtraitTraits determined by two ormore genes, or by the interaction ofgenes with the environment.3-4
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-4 Exceptions to Exceptions to Mendelian Mendelian pattern of inheritance pattern of inheritance Single-gene trait gene trait Pairs of alleles show deviations from complete dominance and Pairs of alleles show deviations from complete dominance and recessiveness recessiveness. Different forms of the gene are not limited to two alleles. Different forms of the gene are not limited to two alleles. One gene may determine more than one trait. One gene may determine more than one trait. Multifactorial Multifactorial trait Traits determined by two or more genes, or by the interaction of Traits determined by two or more genes, or by the interaction of genes with the environment. genes with the environment
3.1 Extensions to Mendelfor single-gene inheritance3-5
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 3-5 3.1 Extensions to Mendel for single 3.1 Extensions to Mendel for single -gene inheritance gene inheritance