The Basic Difference in Constitution between the Mammalian X and the Drosophila X
During the course of evolution progressive genetic deterioration occurred to the Y-chromosome. As a result, the Y-chromosome of placental mammals became a highly specialized male-determiner, having but one function namely to induce the indifferent embryonic gonad to develop as testis. The consequence of this specialization by the Y was that almost all of the original Mendelian genes which had been maintained by the X-chromosome, had to accommodate themselves to a hemizygous existence in the heterogametic male sex. The hemizygous existence for all the genes on the X should be very perilous since monosomy for even the smallest autosome (only one-fourth the size of the X) is apparently lethal in man.
KeywordsInterphase Nucleus Placental Mammal Dosage Compensation Meiotic Prophase Heterochromatic Region
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