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Ch. 5 - Chromosome Mapping in Eukaryotes
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All textbooksKlug 12th EditionCh. 5 - Chromosome Mapping in EukaryotesProblem 7

Chapter 5, Problem 7

What is the proposed basis for positive interference?

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Hello everyone and welcome to today's video. So today we have that. It has been observed that in the maze cross only 7.8% of the double crossover are observed Compared to an expected 9.7%. Which of the following phenomena is responsible for such an observation. Let's go over each of our answer choices so that we may solve the problem and situates a state's linkage. Remember that linkage refers to genes in a chromosome that are very close together. These jeans are going to be linked and they're usually going to be inherited together. This is not really causing the decrease in the observed number of crows over. So we're going to cancel it out. Then we have a p stasis and stasis refers to an interaction Between two genes that could have a certain effect on a phenotype. Again, this is not what the question is asking for. So we're going to cancel it out. Then we have coincidence and coincidence itself is called also the coefficient of coincidence. It measures they observed in this case 7.9 divided by the expected number of crossover events. This is not really what the question is asking for because the question is asking for the phenomenon responsible not the actual coefficient of coincidence. So we're going to cancel it out. And finally we have interference. And interference is when a crossover event on a nearby area of the chromosome inhibits the following crossover events in the nearby area of the chromosomes because of this, the crossover events are going to be decrease. Which is what we're seeing in the problem. So answer choice. The interference is the correct answer to our question. I really hope this video helped you, and I hope to see you on the next one.
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Textbook Question
Why does more crossing over occur between two distantly linked genes than between two genes that are very close together on the same chromosome?
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Explain why a 50 percent recovery of single-crossover products is the upper limit, even when crossing over always occurs between two linked genes?
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Why are double-crossover events expected less frequently than single-crossover events?
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What two essential criteria must be met in order to execute a successful mapping cross?
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The genes dumpy (dp), clot (cl), and apterous (ap) are linked on chromosome II of Drosophila. In a series of two-point mapping crosses, the following genetic distances were determined. What is the sequence of the three genes? dp–ap 42 dp–cl 3 ap–cl 39
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Textbook Question
Colored aleurone in the kernels of corn is due to the dominant allele R. The recessive allele r, when homozygous, produces colorless aleurone. The plant color (not the kernel color) is controlled by another gene with two alleles, Y and y. The dominant Y allele results in green color, whereas the homozygous presence of the recessive y allele causes the plant to appear yellow. In a testcross between a plant of unknown genotype and phenotype and a plant that is homozygous recessive for both traits, the following progeny were obtained: colored, green 88 colored, yellow 12 colorless, green 8 colorless, yellow 92 Explain how these results were obtained by determining the exact genotype and phenotype of the unknown plant, including the precise arrangement of the alleles on the homologs.
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