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Chapter 6-1.docx

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BIOL 2000
Joseph Rasmussen

Chapter 6-1 Definition Pleiotropic mutation- a mutation that affects several different phenotypic charactertistcs Haplosufficiency- a single dose of the wild type allele can confer the wild type phenotype in a diploid cell Haploinsufficiency- a single dose of the wild type allele cannot confer the wild type phenotype in a diploid cell/organism Dominant negative- a mutant allele that in one dose as in a heterozygous individual, can eliminate the wild type function resulting in the mutant phenotype Co-dominance- alleles which, when combined in the heterozygote show aspects fo both homozygotes Incomplete dominance- Alleles which, when combined in the heterozygote show a phenotype intermediate between the homozygotes Mendel’s findings  One gene, two alleles  Each gene controls a single different character  One alleles is completely dominant to the other Ratios:  3:1 = 1:2:1 monohybrid selfed  9:3:3:1 Dihybrid selfed  1:1 Monohybrid test crosses  1:1:1:1 Dihybrid test crosses  If genes in Dihybrid are linked, frequencies shift towards parental  Complexity arises: o A gene may have multiple alleles o A gene may be pleiotropic  More then one gene may control a single characteristic Interaction between alleles of a single gene: Variations of dominance  So farm we have considered only cases where one allele is fully (completely) dominant over another o Aa = AA phenotype  Case I: Wild type allele is fully dominant to the mutant allele o One dose of the wild type allele is enough for wild type phenotype= haplosufficent  Case II: Mutant allele is fully dominant to the wild type (recessive wild type) o One doe of the wild type allele is not enough for wild phenotype= haploinsufficent  Wild allele makes up 30 units of a protein, and 40 are required for wild type phenotype. A null mutation (0units ) will be dominant  + = 30 units  ++ = 60 units  m = 0 units  +m= 30 units o Mutant phenotype as less then 40 units  For leaky: o +=30 units o ++ = 60 units o l = 15 units o +l = 45 units  Phenotype is wild type. Leaky allele is recessive to wild type. o OR The mutant allele (dominant negative) makes the wild type allele non-functional  Gene product forms a homodimer, and one defective polypeptide interferes with its function Clicker  For gene wg controls formation of wings. For a cell to become part of the wing, it requires 50 units of the wg gene product; if a cell has less then 50 units it will not become part of the wing. The wild type wg+ allele makes 30 units of the wg gene product; a mutant allele (wg) makes 0 units of the wg
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