tailieunhanh - Ebook Genetics from genes to genomes: Part 2

(BQ) Part 2 book "Genetics from genes to genomes" presents the following contents: How genes travel on chromosomes, how genes are regulated, beyond the individual gene and genome. Invite you to consult. | CHAPTER Mouse mitotic metaphase chromosomes stained for karyotype analysis magnification 600X . PART IV How Genes Travel on Chromosomes The Eukaryotic Chromosome To build an artificial chromosome able to function as part of a cellular genome what chromosomal components would you need to assemble Three sets of observations help answer this question. In Chapter 4 you saw that when chromosomes segregate during mitosis or meiosis some of the cell s newly elongated spindle fibers attach to the centromere the pinched-in portion of the chromosome viewed under the microscope Fig. . A centromere is therefore essential to proper chromosome segregation. Second scientists have found that the ends of linear chromosomes remain intact even though linear pieces of DNA when introduced into a cell are susceptible to degradation by nucleases. A search for the chromosomal element that prevents degradation revealed that specific repeated DNA sequences and special proteins compose the tips of linear chromosomes. Known as telomeres these protective DNA-protein caps are another critical chromosome component. Finally you know that DNA must replicate before cell division so that each daughter cell receives a complete copy of the genomic DNA. To ensure that your artificial chromosome replicates properly you must include at least one origin of replication. In the 1980s molecular geneticists took these three key chromosomal elements centromeres telomeres and origins of replication and using raw materials from the yeast Saccharomyces cerevi-siae constructed the first artificial eukaryotic chromosome known appropriately as a yeast artificial chromosome or YAC. Single-celled yeast was the organism of choice because it is easy to manipulate its genetic machinery resembles that found in the cells of higher organisms and it is so far the only eukaryotic organism whose origins of replication centromeres and telomeres have been defined as discrete small segments of DNA. Yeast cells have 16 .