Explanations of selected Gonzo Genetics Problems

Explanations of selected Gonzo Genetics Problems -...

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Explanations of selected Gonzo Genetics Problems: Questions #1 through 3 . The key here is to realize that the stage in the life cycle of the organism when the phenotype will be revealed is the haploid stage. Therefore there is no dominant and recessive because there is only one homolog and therefore only one allele. Whatever allele the next generation haploid adult inherits, that’s what its phenotype is. All the gametes from an adult will have the same genotype as the adult (no meiosis and segregation of alleles is necessary to produce gametes because it is already haploid – which explains the answer to question #2 ). However, the chromosomes and alleles from two adults mix in the diploid sporophyte and undergo meiosis to generate a haploid adults with new mixtures of chromosomes (which explains why you do get recombination in question #3 ). Another way of thinking of it is that it is just like standard Mendelian genetics except the haploid gametes have the phenotype instead of the diploid adult. Each generation consists of a pair of haploid gametes giving rise to the next generation of haploid gametes via an intermediate diploid stage that undergoes meiosis. Question #4 through #7. The point of these questions is to illustrate the relationship between map distance and recombination frequency. If there is exactly one recombination event per homologous pair of chromosomes then there will be exactly two recombinant chromatids and two non recombinant chromatids (one of each for each homologous chromosome). In question #4 the genes for dumpy and twisted are at the extreme ends of the chromosome, therefore the recombination event must occur in between them. Thus, the gametes from the heterozygote must have equal proportions of each possible genotype. Since you are crossing to a homozygous recessive, so will the progeny. If you calculate the map distance, it will be 50cM. Question #5 is the same except the Clr gene is in the middle of the chromosome. From the previous question we know the total map distance across the chromosome is 50cM (end to end), and map distance is proportional
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This note was uploaded on 04/07/2010 for the course BIOL biol 112 taught by Professor Dent during the Winter '10 term at McGill.

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Explanations of selected Gonzo Genetics Problems -...

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