Maternal influence on sex determination

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In humans and many other species of animals, the father determines the sex of the child. In the XY sex-determination system, the female-provided ovum contributes an X chromosome and the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively.

Hormone levels in the male parent affect the sex ratio of sperm in humans.[1] Maternal influences also impact which sperm are more likely to achieve conception.

Human ova, like those of other mammals, are covered with a thick translucent layer called the zona pellucida, which the sperm must penetrate to fertilize the egg. Once viewed simply as an impediment to fertilization, recent research indicates the zona pellucida may instead function as a sophisticated biological security system that chemically controls the entry of the sperm into the egg and protects the fertilized egg from additional sperm.[2]

Recent research indicates that human ova may produce a chemical which appears to attract sperm and influence their swimming motion. However, not all sperm are positively impacted; some appear to remain uninfluenced and some actually move away from the egg.[3]

The time at which insemination occurs during the oestrus cycle has been found to affect the sex ratio of the offspring of humans, cattle, hamsters, and other mammals.[1] Hormonal and pH conditions within the female reproductive tract vary with time, and this affects the sex ratio of the sperm that reach the egg.[1]

Sex-specific mortality of embryos also occurs.[1]

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References[edit]

  1. ^ a b c d Krackow, S. (1995). "Potential mechanisms for sex ratio adjustment in mammals and birds". Biological Reviews 70 (2): 225–241. doi:10.1111/j.1469-185X.1995.tb01066.x. 
  2. ^ Suzanne Wymelenberg, Science and Babies, National Academy Press, 1990, page 17
  3. ^ Richard E. Jones and Kristin H. Lopez, Human Reproductive Biology, Third Edition, Elsevier, 2006, page 238

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