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The progress of epigenetic research has led to the discovery and confirmation of age-related markers based on DNA methylation. These DNA methylation indices are called "epigenetic clock/age". The concept of "epigenetic clock/age" and the establishment of its evaluation system are helpful to solve some of the long-standing problems in the field of life and medicine. When facing the current global aging, it is of great significance to refer to the comprehensive health parameters to determine the biological age and life span of an individual, and thus to design a plan to slow down the process of life cycle. This paper has summarized the concept and development of "epigenetic clock/age" in recent years.

Two novel body marking mutants were discovered during silkworm (Bombyx mori) breeding. The mutants have no obvious eye-spots compared with normal marking (+) individuals, but their star spots and semilunar markings on dorsal sides are normal, and there are dots and lines with longitudinal wave markings on dorsal sides of the 6th to 7th abdominal segments which consist quail markings in between star spots and semilunar markings. The whole body markings are very similar to that of quail mutant (q); thus these mutants are named as quail-like mutants (q-l). Young larvae of one mutant are in brown color, and develop normally. Their cocoons are regular and uniform in size. Thus, this mutant is designated as brown quail-like (q-lb). Another mutant's larvae are in light purple skin; thus this mutant is named as purple quail-like (q-lp). They take little amount of mulberry leaves, and are weak and develop slowly and unevenly. Their larval bodies and cocoons are small. Genetic analysis revealed that both q-lb and q-lp were recessive genes, and they were allelic, with q-lb recessive to q-lp. These genes are different from quail mutant (q) and located on the chromosome 8 after tested by the morphological markers, P3(2), p(2), Ze(3), L(4), re(5), E(6), q(7), I-a(9), ms(12), ch(13), oa(14), cts(16), mln(18), msn(19), rb(21) and so(26) and SSR markers.