Discovering the biological sex of the baby is an eagerly anticipated event during pregnancy. A baby's sex is determined during fertilization, but the gender reveal typically happens later with the aid of ultrasound and healthcare professionals.
What Determines a Baby's Sex? Exploring the Role of X and Y Chromosomes at Birth
Factors in Determining the Baby's Sex
The terms "biological sex" and "gender" are often used interchangeably for babies, but they have distinct meanings, according to an article in Health. Biological sex pertains to the male, female, or other sex assigned at birth based on physical characteristics, while gender refers to the sociocultural roles or behaviors associated with one's sex.
An individual's biological sex is determined by the sex chromosome present in the sperm, which could be either X or Y. Human sex chromosomes consist of the X and Y chromosomes, with most people having one pair in their cells.
Those assigned males at birth possess an X and Y chromosome, while those assigned females have two X chromosomes. However, in some cases of fertilization, rare occurrences of additional or missing sex chromosomes may alter the development of biological sex characteristics.
For instance, biologically developing as a male without a Y chromosome can lead to features such as small testes, undescended testes, or a urethra opening on the bottom side of the penis. Some individuals may even have ambiguous genitalia that are neither male nor female in appearance.
On the other hand, developing biologically as a male with an extra Y chromosome typically results in typical male sex features, and the person may be taller than average.
In the case of having both extra X and Y chromosomes, the additional genetic material from the X chromosome can influence the development of biological sex features, resulting in small testes and enlarged breasts.
Gene Regulator Decides a Baby's Sex
Researchers at Melbourne's Murdoch Children's Research Institute revealed a revolutionary finding concerning how a baby's sex is decided in 2018, according to Science Daily. They discovered that it involves a "regulator" that regulates the action of genes that determine whether an individual is male or female.
The study published in Nature Communications focused on enhancers, segments of DNA that do not contain genes but play a critical role in increasing or decreasing gene activity. If these enhancers that control testis genes are disturbed, a kid may be born with a sex development abnormality.
The researchers discovered three enhancers that cooperate to guarantee that the SOX9 gene is activated at a high level in an XY embryo, resulting in proper testis and male development.
Surprisingly, they found XX patients who carried extra copies of these enhancers and developed testes instead of ovaries, and XY patients who lost these enhancers and developed ovaries instead of testes. This demonstrated that human sex reversal can be caused by the gain or loss of these vital enhancers regulating the SOX9 gene.
Professor Andrew Sinclair, the lead author of the study, highlighted the significance of looking beyond the genes and focusing on enhancers to diagnose these conditions properly.
Enhancers, which account for about one million across the human genome, have been found to control about 22,000 genes and reside in the so-called "junk DNA or dark matter." Understanding these enhancers could potentially unlock the key to diagnosing various disorders and shed light on the poorly understood regions of our DNA.
RELATED ARTICLE: Y Chromosomes Shed Light Why Men Function Differently Than Women
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