Practise AP Biology 5.2.A questions by explaining how crossing over, independent assortment and nondisjunction affect gamete variation.
Crossing over in meiosis I is required for homologous chromosomes to properly align during metaphase and segregate during the first cell division.
Explain why some haploid cells formed after meiosis in this experiment will have only one fluorescent marker.
The scientists then investigated whether attaching individual kinetochore proteins to a specific DNA sequence present in a known crossing-over hotspot on chromosome 8 affected the frequency of crossing over at this location. In their first experiment, they examined three groups of yeast cells containing the modified chromosome 8. Group 1 contained no kinetochore proteins attached to the hotspot, group 2 contained the kinetochore protein CTF attached to the hotspot, and group 3 contained the kinetochore protein IML attached to the hotspot. For each group, the scientists determined the frequency of crossing over between the RFP and GFP genes. To determine the frequency, the scientists added the number of cells emitting both red and green light to the number of cells that emitted no light and divided by the total number of cells (Figure 2).
Figure 2. The frequency of crossing over in a hotspot on yeast chromosome 8 for cell groups treated with different kinetochore proteins. Error bars represent \(\pm 2 \mathrm{SE
Based on Figure 2, describe the effect on the frequency of crossing over when CTF is attached to the chromosome 8 hotspot compared with the effect when IML is attached to the hotspot.
Predict the effect on the number of copies of chromosome 8 likely to be present in the resulting daughter cells when CTF is attached to the hotspot.
Provide reasoning to justify your prediction.
Explain how the presence of hotspots (Figure 1) could increase the likelihood that a population will survive in the presence of selective pressures.
Write your responses to this question only on the designated pages in the separate Free Response booklet. If there are multiple parts to this question, write the part letter with your response.