One of the problems faced by organisms with a heterogametic sex is successful y
ID: 74005 • Letter: O
Question
One of the problems faced by organisms with a heterogametic sex is successful y pairing and segregating the non-homologous sex chromosomes. During meiotic prophase in mamma s, e sex chromosomes X and Y show a characteristic allocyclic (outside of the normal cycle) behavior, i.e., they condense earlier and remain condensed longer than the autosomes. Light microscopic observations of mammalian meiotic cells reveal the sex chromosomes forming a mass of condensed chromatin attached to the nuclear envelope: the so-called sex vesicle or XY body. This body behaves in a different manner than synapsed homologous chromosomes, but none the less segregates at anaphase I. A research group searched for and found a monoclonal antibody specific for the sex vesicle. The antibody bound only to the sex vesicle. The protein disappears after disjunction. We still don t know what the protein does, but it appears to be involved in the interaction that keeps the non-homologous sex chromosomes paired. Figures 1 and 2 below represent the testis and ovary and the gametogenic process. If you were to use this antibody to the sex vesicle to immunostain the tissues represented here, where would you expect to see staining? Indicate by circling the appropriate cells. Explain.Explanation / Answer
The sex vesicle will be visible in the fertilized egg and the cells after that, in the 2 cell stage, 4, cell stage, blastocyte stage the sex vesicle will be visible. Because the barr body formation occurs after fertilization after which the extra X chromosome in female is inactivated. Hence the above said stages will show the staining of sex vesicle.
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