Genetics3 - 41 Exceptions to Mendelian Inheritance...

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Exceptions to Mendelian Inheritance • Incomplete Dominance • Codominance • Epistasis • Linkage 41
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10-12 Incomplete dominance follows Mendel’s laws 42 If dominance=complete Heterozygote = dominant phenotype Heterozygotes show intermediate phenotype F1 appears blended F2 = parental traits reappear
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Codominance • Both alleles of a gene can express their phenotype simultaneously • Alleles follow normal Mendelian inheritance patterns so genotypic patterns are identical with simple dominant/recessive alleles. Phenotype of heterozygote is critical difference • ABO blood groups are an example 43
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Early attempts at blood transfusion frequently killed patients because of incompatible blood groups Around 1900, Austrian scientist = Karl Landsteiner Mixed blood cells and serum from different individuals Found only certain combinations were compatible Otherwise rbc formed clumps when mixed with serum from others Clumps form because of antibodies in serum that react with foreign Proteins on surface of non-self cells ( antigens )
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Figure 10.13 ABO Blood Reactions Are Important in Transfusions 44
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Structural Basis of ABO Antigens 45
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ABO blood groups in US population ABO blood groups in US population 46 Often alleles don’t show simple dominant-recessive pattern
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Existing alleles are subject to mutation = give rise to new alleles = multiple alleles for 1 character Mutant alleles = different phenotype Many genes have multiple alleles
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• Alleles occupy same genetic locus on homologous chromosomes • Segregate with Mendelian monohybrid ratios, 3:1, 1:2:1, 1:1 depending on cross. • A gene can have many hundreds of different alleles but each diploid individual carries only two alleles for each gene. 47
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This note was uploaded on 10/16/2010 for the course MCDB MCDB 1A taught by Professor Senghuilow during the Spring '09 term at UCSB.

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Genetics3 - 41 Exceptions to Mendelian Inheritance...

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