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Chapter 7: Problem 23

In Creighton and McClintock's experiment demonstrating that crossing over involves physical exchange between chromosomes (see Section 7.6 ), explain the importance of the cytological markers (the translocated segment and the chromosome knob) in the experimental rationale.

Short Answer

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Answer: Cytological markers, such as the translocated segment and the chromosome knob, played a crucial role in Creighton and McClintock's experiment as they allowed the researchers to visually track the exchange of genetic material between homologous chromosomes during meiosis. These markers provided clear, visible proof of the physical exchange of genetic material, making the experimental results more reliable and providing strong evidence for the process of crossing over during meiosis. Without these markers, it would have been extremely difficult to directly observe and verify the physical exchange between chromosomes.

Step by step solution

01

Understanding Creighton and McClintock's experiment

In their experiment, Creighton and McClintock used maize plants to study the process of crossing over. They used a specific type of corn that had chromosomes with unique visible features called cytological markers. One marker was a translocated segment and the other was a chromosome knob. By tracking these markers, they were able to observe the physical exchange of genetic material between homologous chromosomes during meiosis.
02

The role of cytological markers in the experiment

The cytological markers, the translocated segment, and the chromosome knob played a crucial role in Creighton and McClintock's experiment. These visible markers allowed them to visually track the exchange of genetic material between homologous chromosomes during meiosis. The presence of the markers made it easier to observe and analyze the exchange of genetic material and the process of crossing over.
03

The importance of cytological markers in the experimental rationale

The importance of the cytological markers lies in the fact that they provided clear, visible proof of the physical exchange of genetic material during meiosis. Without these markers, it would have been extremely difficult, if not impossible, to directly observe and verify the physical exchange between chromosomes. The presence of the markers made the experimental results more reliable and provided strong evidence for the process of crossing over during meiosis. The cytological markers acted as a vital tool that allowed Creighton and McClintock to show the physical aspect of genetic exchange, thus supporting the importance of crossing over in genetic recombination.

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Most popular questions from this chapter

A female of genotype \\[ \frac{a}{+++} \\] produces 100 meiotic tetrads. Of these, 68 show no crossover events. Of the remaining 32,20 show a crossover between \(a\) and \(b\), 10 show a crossover between \(b\) and \(c,\) and 2 show a double crossover between \(a\) and \(b\) and between \(b\) and \(c .\) Of the 400 gametes produced, how many of each of the eight different genotypes will be produced? Assuming the order \(a-b-c\) and the allele arrangement shown above, what is the map distance between these loci?

What three essential criteria must be met in order to execute a successful mapping cross?

Drosophila females homozygous for the third chromosomal genes pink eye (p) and ebony body (e) were crossed with males homozygous for the second chromosomal gene dumpy wings (dp). Because these genes are recessive, all offspring were wild type (normal). \(F_{1}\) females were testcrossed to triply recessive males. If we assume that the two linked genes ( \(p\) and \(e\) ) are 20 mu apart, predict the results of this cross. If the reciprocal cross were made (F1 males-where no crossing over occurs-with triply recessive females), how would the results vary, if at all?

The genes dumpy wings \((d p),\) clot eyes \((c l),\) and apterous wings \((a p)\) are linked on chromosome II of Drosophila. In a series of twopoint mapping crosses, the genetic distances shown below were determined. What is the sequence of the three genes?

In Drosophila, the two mutations Stubble bristles (Sb) and curled wings ( $c u$ ) are linked on chromosome III. Sb is a dominant gene that is lethal in a homozygous state, and \(c u\) is a recessive gene. If a female of the genotype \\[ \frac{S b}{+} \\] is to be mated to detect recombinants among her offspring, what male genotype would you choose as her mate?
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