Question

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

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

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.

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.

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.