lec 5 Gene Interaction_posted

lec 5 Gene Interaction_posted - Understanding the concept...

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Gene (DNA) Gene product (usually protein) Wild-type alleles perform a normal biological function, and are usually dominant function function AA A and a are alleles of a gene, where A is dominant and a is recessive Genotype phenotype aa no function no function Aa function no function Mutated alleles that lack biological function are usually recessive Heterozygosity for wild-type and mutant allele still results in function = Dominance A a a a A A Understanding the concept of Dominance
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The complementation test two recessive mutations (1 and 2) are independently isolated. Homozygosity for these mutations results in similar phenotypes. Are they alleles of the same gene or of different genes? intercross individuals carrying mutations to create a hybrid and score phenotype in hybrid if same gene a 1 / a 1 x a 2 / a 2 a 1 / a 2 a 1 / a 1 a 2 / a 2 a 1 / a 2 no function no function no function phenotype phenotype phenotype if different genes a 1 / a 1 ; b + / b + x a + / a + ; b 2 / b 2 a 1 / a + ; b 2 / b + a 1 / a 1 ; b + / b + a + / a + ; b 2 / b 2 a 1 / a + ; b 2 / b + no A function no B function function phenotype phenotype wild-type mutations in the same gene do NOT complement mutations in different genes complement
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x x x x Incomplete Dominance ( = partial dominance, = semidominance) red white pink pink red white white red 1 red : 2 pink : 1 white AA aa Aa Aa AA aa 0 Enzyme activity genotype 0.5 1.0 AA Aa aa precursor red pigment A compare to complete dominance 0 genotype 0.5 1.0 Gradual response - no threshold Threshold level for full pigmentation A a A a aa AA Aa Aa 1 2 1
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Multiple alleles Genes can be mutated in many ways e.g. a typical size gene of 2,000 base pairs could have 6,000 different forms Rules: - a gamete can normally contain only one allele - an organism or cell contains up to two different alleles - a population of organisms may contain any number of alleles from Mendel’s principles New antimorphic: antagonizes normal function (poison) amorphic: complete loss of function (= null) Hypomorphic: reduced function wild-type: normal function hypermorphic: increased function neomorphic: new function eyl anti / eyl + eyl 0 / eyl 0 eyl 1 / eyl 1 eyl 2 / eyl 2 eyl + / eyl + eyl hyper / eyl + eyl neo / eyl + Allelic series less function more function Dominant Dominant Dominant Dominant Recessive Recessive
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Multiple alleles and codominance Blood type: I gene Precursor carbohydrate A-antigen (precursor + N-acetylgalactosamine) B-antigen (precursor + galactose) unmodified precursor Recognized by antibody anti - A anti - B none Genotype antigen expressed Blood type antibodies expressed compatible donor blood type* compatible recipient blood types I A I A I A I 0 I B I B I B I 0 I A I B I 0 I 0 A B A,B none A B AB O A, O B, O A, AB B, AB AB A,B, AB , 0 Dominance relationships: I A and I B are dominant over I 0 I A and I B are codominant anti-B I B I A I 0 anti-A none anti-B, anti-A recipient must lack anti-A coagulates RBCs that have B antigen (i.e. B or AB) I o I o is the universal donor O A, B, AB, O Autoimmunity is prevented by suppressing production of antibodies that recognize a host antigen.
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This note was uploaded on 07/17/2011 for the course BIO 151 taught by Professor Grinblat during the Summer '08 term at University of Wisconsin.

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lec 5 Gene Interaction_posted - Understanding the concept...

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