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Boy or Girl: How Genetics Determines Your Baby's Gender

By Varsha

Couples expecting a baby are always eager to know every bit of information related to their baby. Right from the health of the fetus, to the baby's overall development, its response to dietary routine or changes as prescribed by the doctor, and so on.

Many of them are also curious to know the gender of the baby, whether they would welcome a baby girl or a baby boy. Are you aware what the deciding factor of the baby's gender is?

How does genetics determine the baby's gender? Which of the parents determine the sex of the baby? If you are curious to know about these aspects, read on to know how genes establish the gender of babies.

The Gender Is Determined At The Time Of Conception

During conception itself, the gender of the baby is determined by one of the chromosomes - X or Y- from the sperm cell of the father. When the sperm cell fertilizes the egg, the chromosome in it fuse with the X chromosome in the egg cell to form the baby which may be:

X (egg cell) + X (sperm cell) = XX, i.e., female, or

X (egg cell) + Y (sperm cell) = XY, i.e., male

Basically, the possibility of a boy or a girl may be taken as 50% each for almost everyone.

According to a study conducted on mice, a baby is genetically more like the father, than the mother. The reason for this being the DNA passed down from the father, which is more than what is passed down from the mother. The study concluded that this most likely applies to all mammals (including humans) as well.

Sexual Development And Differentiation Of A Fetus

During the 2nd month of pregnancy, i.e., roughly seven to eight weeks after conception, the fetus starts developing the external sexual organs. Till then, it looks neutral, i.e., neither as a female or a male. Gradually after the 2nd month, the fetus starts producing hormones, thereby causing the sex organs to grow further to be male or female organs. This process is known as the sexual development and sexual differentiation.

The Shuffling And Re-Shuffling Of Genes Over Generations

Yes! You read that right. The genes do get shuffled and re-shuffled as each generation progresses. It's a known fact that mother is the source of half of genes of a baby, and the other half comes from the father. Similarly, each parent would have inherited half genes from each of their respective parents. Which means, the grandparents would be the source of one quarter of genes of the baby.

Is It Possible To Predict The Gender Of The Baby By The Family History?

A study by the Newcastle University involves assisting numerous prospective parents figure out the probability of them having daughters or sons. The findings of the research state that men inherit the tendency to have daughters or sons from their parents. In simple terms, if a man has more brothers, he may have sons, and if he has more sisters, he may have daughters.

How Do Genes Determine Whether It Would Be A Boy Or A Girl?

Genes are inherited from both the parents, and comprise two parts called as alleles. Following are the three combinations which manage the X & Y chromosomes in a man's sperm:

1. mm: This combination is responsible for more sons for the man, since it produces more Y chromosome.

2. mf: It produces the equal number of X and Y, which leads to an equal number of sons and daughters.

3. ff: This combination produces more X chromosome, and therefore results in more daughters.

Myths Vs Facts About Predicting The Baby's Gender

• Fetal heart rate: Determining the baby's gender by its heart-rate per minute has been a popular theory. In case the fetal heart rate is more than 140BPM , i.e., beats per minute, then the baby may be a girl, and if it is less than 140 BPM, then it is more likely to be a boy.

However, it may be confusing if the heart rate is within the normal beat range of 120-140BPM. Although this seems to be an interesting way of predicting the gender, there is no scientific proof of it!

Several studies were conducted to figure out the connection, if any. However, the results were always negative. So, we can say this method can sort of help predict the baby's gender, but is only assumption-based.

• Carrying the baby weight high or around the middle: It is said that a woman carrying her baby high or around the middle, may have a baby girl. However, if the baby bump is in front, then it may be a baby boy! This is an outright myth, since the shape, size, height, weight, etc. of the mother's belly will have absolutely no relation to the baby's gender.

• Oily skin or pimples: Another classic example of a myth in pregnancy is - 'In case the mother is carrying a baby girl, it may lead to her skin becoming oily and breaking out.' There is no fact in this, and only the hormones need to be blamed for it!

• Terrible and unpredictable mood swings: A baby girl is termed a reason for extreme mood swings, however, in actual, it will only be related to any sort of hormonal changes within the mother, and could even happen to mothers carrying a baby boy.

• Sweet or salt cravings: Sweet cravings during pregnancy are attributed to a baby girl, and salt cravings to a baby boy. But, this is not true. The cravings only happen due to the deficiency of certain nutrients, and have no connection to the gender.

Other Possible Ways/Situations To Determine The Baby's Gender

An ultrasound after 20-22 weeks into pregnancy is helpful in providing around 90% accurate information regarding the baby's gender. Also, in case of mothers experiencing genetic disorders or chromosomal anomalies in their fetus could get to know the gender through invasive tests such as amniocentesis or chorionic villus sampling.


Apart from genetics-related mechanisms, certain environmental aspects have a probability of influencing the gender of the baby. However, there has not been any definite information regarding this.

Numerous studies conducted on multiple environmental factors have yielded inconsistent and unreliable results. Therefore, only the genetics mechanisms happen to be the most reliable way of predicting the baby's gender as of now.

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