BIOL239 Study Guide - Final Guide: Dihybrid Cross, Allele Frequency, Genotype Frequency
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16 Oct 2011
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Phenotype - observable characteristic (largely determined by genotype). Monohybrid cross matings between individuals that only differ in one trait. Allele alternative form of a single gene. Polymorphic more then one wildtype allele; allele frequency greater than 1% Monomorphic only one wildtype allele; only one allele above 1% frequency. The two alleles for each trait separate (segregate) during gamete formation then unite at random, one from each parent, at fertilization. At the dna level, alleles vary in nucleotide sequence. This can result in: new amino acid sequence, change in the amount of protein, e. g. Garden peas r gives the pea a round shape because this version of the starch. The r allele as a different amino acid sequence and the enzyme is non-functional (i. e. no branched starch). Test cross breeding an unknown genotype with the homozygous recessive will reveal its genotype. If it was homozygous dominant, all progeny are heterozygous and have the same phenotype.
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These all relate to exceptions to the inheritance patterns encountered by Mendel.â
Why do multiple and lethal alleles often result in modifications of the classic Mendelian monohybrid and dihybrid ratios?
Select the four correct statements.
-When an essential gene is mutated, it can result in a lethal phenotype. There are no classic Mendelian monohybrid and dihybrid ratios. |
-In the case of codominance, heterozygotes produce gene products from both alleles of a gene. Classic Mendelian monohybrid and dihybrid ratios are modified by codominance. |
-In the case of incomplete dominance, the phenotype of the heterozygote is distinct from and often intermediate to the phenotypes of homozygous individuals. Classic Mendelian monohybrid and dihybrid ratios are modified by incomplete dominance. |
-Genes exist in a large number of allelic versions and a diploid organism has two homologous gene loci that may be occupied by different alleles of the same gene. This can result in many different phenotypes for traits, which may not follow typical Mendelian ratios. |
-When an essential gene is mutated, it can result in a lethal phenotype. This results in a modification of classic Mendelian ratios. |
-The phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. The joint expression of both alleles in a heterozygote is called codominance. There are no classic Mendelian monohybrid and dihybrid ratios. |
-Genes exist in a large number of allelic versions, but in a diploid organism, only one allele of the gene can occupy one homologous gene loci. Classic Mendelian inheritance cannot explain this phenomenon. |
-Each gene produces a unique gene product. The effect of one allele in a heterozygote completely masks the effect of the other. Classic Mendelian genetics cannot explain this phenomenon. |