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Opposite sex in identical twins: Does it really happen?

From conventional wisdom, we know that in humans twinning results from one of two possible events:  The mother's ovaries release two oocytes (eggs) and two sperm from the father fertilize each the eggs = dizygotic or fraternal twins. The ovaries release one oocyte and it is fertilized by one sperm; however, the zygote (the fertilized egg) splits into two separate embryos = monozygotic or identical twins . Since fraternal twins come from completely unique gametes (sperm and egg), fraternal twins can be of opposite sex or the same sex. For example, if a sperm carrying a Y chromosome fertilized one oocyte and another sperm carrying an X chromosome fertilized the other (remember: the oocytes from the mother all carry one X chromosome) the result would be one boy (XY) and one girl (XX) fetus. If sex chromosomes from each sperm were both X chromosomes, both fetuses would be female. Similarly, if both spermatozoa carried Y chromosomes, the resulting fetuses would both be
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Male genital tract infection is a risk factor for developing infertility

In May of this year, Hans-Christian Schuppe , Wolfgang Weidner and colleagues from Justus-Liebig University in Germany published the article "Urogenital Infection as a Risk Factor for Male Infertility" Infertility is a global health issue that affects an estimated 15% of reproductive-age couples. Infertility is defined by the World Health Organization (WHO) as the inability to conceive after 1 full year of unprotected intercourse. The causes of infertility in males and females are numerous, and it is believed that at least half of all cases of infertility in couples are caused by issues with the male partner. Though there are several identified causes of male infertility such as varicocele (varicose veins in the testis) and chromosome defects, the review article by Schuppe et al.  highlighted the contribution of urogenital infections to male infertility. From their literature review that included over 90 articles on the subject, the authors summarized 4 disease presentat
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