Carefully consider the result shown in Figure Q5–13. Each of the two colonies shown on the left is a clump of approximately 100,000 yeast cells that has grown up from a single cell, which is now somewhere in the middle of the colony. The two yeast colonies are genetically different, as shown by the chromosomal maps on the right. The yeast Ade2 gene encodes one of the enzymes required for adenine biosynthesis, and the absence of the Ade2 gene product leads to the accumulation of a red pigment. At its normal chromosome location, Ade2 is expressed in all cells. When it is positioned near the telomere, which is highly condensed, Ade2 is no longer expressed. How do you think the white sectors arise? What can you conclude about the propagation of the transcriptional state of the Ade2 gene from mother to daughter cells?

Transcribed Image Text:

white colony of yeast cells red colony of yeast cells with white sectors telomere Ade2 gene at normal location on chromosome telomere Ade2 gene moved close to telomere Figure Q5-13