Question

In some fungi, cell division during meiosis gives rise to an ordered spore sac

containing a row of four haploid spores, as shown in Figure Q19-30A. The
position of each spore within the sac reflects its relation to its neighbors; in other
words, spores that result from the same meiosis II division are positioned next to
each other. You notice that a strain of the fungus produced by crossing a darkcolored
strain with a light-colored strain gives rise mostly to spore sacs as shown
in Figure Q19-30B, with a few spore sacs like those in Figure Q19-30C. Indicate
whether the following statements are correct. Explain your reasoning.
Figure Q19-30
A. Meiosis I and meiosis II in the fungus occur in the reverse order from that
which occurs in humans.
B. Recombination in the fungus can occur during prophase I.
C. Recombination in the fungus cannot occur during prophase II.
D. The spore sacs in Figure Q19-30C result from recombination between the
centromere and the gene responsible for spore color.
E. Recombination has occurred between the gene responsible for spore color
and the end of the chromosome arm.

Answer 1

The studied fungal spore sac patterns suggest that recombination likely occurs during prophase I, not prophase II, and is responsible for the diversity in coloration. Crossovers near the gene responsible for spore color and possibly between the centromere and that gene can produce the observed spore arrangements.

Step-by-step explanation:

The observation of the spore sacs in a strain of fungus resulting in mostly one color pattern with the occasional different spore arrangement can shed light on several aspects of fungal reproduction. To address the given statements:

• Meiosis I and meiosis II occur in the prescribed order in fungi, as they do in humans; therefore, statement A is incorrect.
• Recombination during prophase I is a common feature in most organisms that undergo meiosis, as it happens during the pairing and synapsis of homologous chromosomes; statement B is correct.
• Recombination does not typically occur during prophase II, as the chromosomes are already separated into sister chromatids at this point; statement C is correct.
• The arrangement of spores in the sacs as in Figure Q19-30C could be attributed to a crossover event between the centromere and the color gene; hence, statement D is likely correct.
• The occurrence of different colors in spores within the same sac indicates that recombination could have taken place near the gene responsible for spore color, making statement E correct.

In conclusion, recombination events are responsible for generating the variety in the spore arrangements observed in the fungus, indicating that the color traits are being reshuffled during the sexual reproduction process.