A Father’s Genes Determine the Sex of a Baby

During a pregnancy, some of the most anticipated news an expecting couple wants to hear about is the gender of their new baby. Whether the baby is a boy or a girl really just depends on chance… or does it? According to a study by Newcastle University, new research suggests that the father’s genes actually play a key role in the likelihood of which gender a baby will be. Work done by Corry Gellatly, a research scientist at the university, has shown that males determine the gender of a baby because of an inherited tendency to have either more sons or daughters that they got from their own parents.

To understand this research, it is important to know that basic reproduction and inheritance shows that a man determines the baby’s gender. The man will combine either an X or Y chromosome with the mother’s X chromosome to produce a girl with the chromosomes XX or a boy with the chromosomes XY. Looking at only this, it would be fair to draw the conclusion that having a baby girl or a baby boy would be a 50/50 toss-up. Up until recently, however, this was the conclusion that was commonly accepted by scientists to explain the seemingly random sex outcomes.

The study conducted by Newcastle University in 2008 would shift the focus of what people thought about reproductive outcomes onto a basis of genes and inherited tendencies. Researchers started by gathering data from 927 family trees containing information from 556,387 people from both Europe and North America dating to the year 1600. With this information, researchers were able to recognize and evaluate the patterns regarding gender inheritance between generations. They found that in families where there were more brothers than sisters, the male offspring would be more likely to have his own kids be boys. Likewise, if a family has more sisters than brothers, the male offspring would be more likely to have his own kids be girls. This pattern can be attributed to an as-yet undiscovered gene that controls whether a man’s sperm contains more X or Y chromosomes that he inherited from his parents.

On a similar note, this gene may also be responsible for the sex ratio in humans, the ratio between men and women, because it determines the liklihood of baby girls and baby boys. “The gene that is passed on from both parents, which causes some men to have more sons and some to have more daughters, may explain why we see the number of men and women roughly balanced in a population,” Gellatly said. “If there are too many males in the population, for example, females will more easily find a mate, so men who have more daughters will pass on more of their genes, causing more females to be born in later generations.”

Because of this research, people are now better able to understand why gender unfolds the way it does. And although we may not have all of the answers regarding this reproductive likelihood, scientists and researchers get closer and closer everyday to understanding nature’s most complex mysteries.

About Mr. Mohn

Biology Teacher

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