Cytogenetics of South American Akodont rodents (Cricetidae). VII. Origin of sex chromosome polymorphism in Akodon azarae.

Publisher Website
Google Scholar
Abstract
A. azarae (Rodentia; Cricetidae) has a sex chromosome polymorphism which gives rise to XX females and females with a partial or total deletion of one X chromosome. Two hypotheses were proposed to explain the findings in A. azarae. In the 1st it is assumed that XX, Xx and XO females are fertile and able to produce X, x and O ova to give XX, Xx and XO females after fertilization by a X-bearing sperm. The 2nd hypothesis proposes and extreme mechanism of sex dosage compensation ranging from X-chromosome inactivation, to partial or total X chromosome elimination. These hypotheses are tested by analyzing the chromosome complement in the offspring derived from mating pairs of A. azarae of known chromosome constitution. The offspring obtained from XX .times. XY mating pairs showed: a sex ratio of 0.67 females/male, an average litter size of 3.8 pups, the lack of Xx or XO femles. The offspring derived from Xx females had: a sex ratio of 1.7 females/male, a ratio of 0.64 XX females per each Xx female, an average litter size of 4.8 pups. The results obtained do not fit the predictions of the fertilization or the sex dosage compensation hypothesis. They can be explained by combining the fertilization hypothesis with a rate of lethality of XX zygotes. The possible cause of the XX zygote lethality and the eventual relationship between sex chromosomal polymorphism and density cycles in natural populations of A. azarae are discussed. Evidence is presented stressing the instability of deleted X chromosomes.