Boy or girl : Who determines gender of the baby, father or mother?
For millennia, scientists and astrologers have attempted to crack the mystery of predicting a baby’s sex
Sure, some of them are fun (like Gender Quiz) but what answers were our ancestors not privy to? What determines the gender of a baby? Put away that telescope— the stars can’t tell you. A microscope might be a better tool for this discovery.
How A Baby’s Gender is Determined: Unlocking the Gender Mystery
We first begin with how a baby is made. We’re referring, of course, to the science of baby-making—not the mechanics.
Let’s start with some reproductive terminology to help paint a picture of what happens on a cellular level.
- Gamete – A gamete is a reproductive cell. Your body is made of a variety of different cells, like muscle cells, immune cells, and brain cells. Each cell has a specific function to help support your body’s health. A gamete’s job is to store your genetic information and use it to create a new life—a baby. There is one type of gamete from each of the two parents – sperm from males and ovum or egg from the females. The sperm and ovum unite to create a baby.
- Sperm – The sperm is the male reproductive cell—also referred to as the male gamete. It holds the father’s DNA and fertilizes the egg to create an embryo, the cluster of cells that grow into a baby. Sperm are made from off puberty, with new cells made daily.
- Ovum or Egg – The ovum is the female reproductive cell, or gamete. It stores the mother’s DNA and is stored and then released from the ovaries. The ovum are developed while the baby is in utero, and no more can be produced. THey are dormant until puberty, and then begin to be releaed with each menstrual cycle.
- Embryo – An embryo is the combination of two cells—a male gamete and a female gamete. When a sperm fertilizes an egg, together, they create an embryo, the cluster of cells that will become a baby.
- Chromosome – The egg and the sperm both carry genetic information in the form of chromosomes. When an egg is fertilized, the male sperm provides half of an embryo’s chromosomes while the egg provides the other half to make a complete set of genetic information—enough to create a new human life.
How does gender fit into this picture?
Chromosomes determine everything from a baby’s eye color to shoe size. The pair of chromosomes that determine a baby’s gender are called sex chromosomes. There are two kinds of sex chromosomes, X or Y.
Women have two X chromosomes while men have one of each kind, an X and Y. To complete the chromosome pair, a mom-to-be’s egg provides one sex chromosome—always an X chromosome—and the sperm provides the other—which has the potential to be either an X or a Y chromosome.
Eggs can only provide an X chromosome because the woman is the source of an egg’s genetic material and women only have X chromosomes. But men have XY chromosomes—that means that a sperm can bring either an X or a Y chromosome to the egg.
If a male sperm carrying an X chromosome fertilizes the egg, it will combine with mom’s X, and the embryo will have two X chromosomes (XX) and become a girl. If a Y-carrying sperm combines with mom’s X, the resulting embryo will have one X and one Y chromosome (XY) and grow up to be a boy.
Men determine the sex of a baby depending on whether their sperm is carrying an X or Y chromosome.
Gender is Determined by the Father
Because sperm cells can carry either of the two sex chromosomes, it’s the male who technically determines the baby’s gender. This raises another interesting question:
Are sperm cells equally likely to contain an X chromosome as they are to contain a Y chromosome?
Thanks to current medical research, it looks like the answer is no.
Evidence 1:
Pew Research investigated the World Bank birth rate data to determine the global sex ratios of males to females.
Historically, they found that the male-to-female birth ratio was around 1.05. Meaning there have been 105 male births for every 100 female births. What’s interesting is that even in countries with the lowest male-to-female birth ratios, they still show a disproportionate share of boys to girls.
It is more likely for a Y chromosome sperm to fuse with an ovam and a boy to be born. This suggests that either there are more Y chromosome sperm cells or that these sperm have a slight edge in the “swimming competition.”
Evidence 2:
The researchers speculate that the creation of sperm cells is likely to be determined by two types of genes. In a simplified scenario:
- If a male has 2 “m” genes, he is more likely to produce Y chromosome sperm and have sons.
- If a male has 1 “m” and 1 “f” gene, he is equally likely to produce either X or Y chromosome sperm.
- If a male has 2 “f” genes, he is more likely to produce X chromosome sperm and have daughters.
Too Many Brothers (or Sisters)
Are there different likelihoods of having a boy or girl?
To summarize, yes, there are different likelihoods of having a boy or a girl. And while the chances may be close to 50-50, evidence suggests that you can look toward the male’s family history and height for some indications as to which direction that chance skews.
The one way to know for sure? An early gender DNA test.
