Sequencing revealed a wide range of base composition changes in the yeast genome.Most yeast chromosomes are composed of GC - rich DNA sequences and GC - deficient DNA sequences.This change in GC content is related to chromosome structure, gene density and recombination frequency.GC contains yeast.
The high-volume regions are generally located in the middle of the chromosome arms, and these regions have higher gene density.Regions with low GC content are generally close to telomere and centromere, and the number of genes in these regions is relatively poor.Simchen et al. confirmed that the relative occurrence rate of the genetic recombination of yeast, namely the double chain fracture, is coupled with the GC enrichment area of chromosomes, and the recombination frequency of different chromosomes is different. The recombination frequency of the smaller I, III, IV and IX chromosomes is higher than the average recombination frequency of the whole genome.
Another distinct feature of the yeast genome is that it contains many DNA repeat sequences, some of which are identical DNA sequences, such as rDNA with CUP1 gene, Ty factor and single LTR sequence derived.High attention has been paid to the large number of nucleotide repeats in the spacing region of genes.Some human genetic diseases are caused by changes in the number of nucleotide repeats.There are more DNA sequences known as genetic redundancy that have higher homology with one another.Multiple chromosomes of yeast have high homologous regions of more than a few dozen KB in length, which are the main regions of genetic abundance, and these regions are still undergoing frequent DNA recombination processes.Another form of genetic abundance is single gene duplication, which is most typical of the dispersion type, and another rare type is the clustering distribution of the gene family.Cluster homology region (CHR) is a large homologous fragment in multiple chromosomes revealed by yeast genome sequencing. Each fragment contains multiple homologous genes corresponding to each other, whose order and transcription direction are very conservative, and there may be insertion or deletion of small fragments.These features suggest that the homologous regions of clustering are intermediate between the duplication of large segments of chromosomes and complete differentiation, and are therefore good materials for studying genome evolution, known as fossils of gene duplication.The chromosome end duplication, single gene duplication and clustering homology region constitute the general structure of yeast genome genetic abundance.Studies have shown that a set of genes in genetic abundance often have the same or similar physiological function, so the mutation of one or a few genes in them cannot show the phenotype that can be distinguished, which is very unfavorable to the functional study of yeast genes.Therefore, many yeast geneticists believe that the understanding of the true nature and functional significance of genetic abundance and the development of experimental methods related to it are the main difficulties and central problems in revealing the function of all genes in the yeast genome.
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