Have you ever wondered why parents with brown eyes can have a child with blue eyes, why in the same family there are men with a lot of hair and others with bald heads, or why there are girls who have their first menstruation at the age of 9 and others at 16?
Many of the personal traits are strongly conditioned by genetics so they can have a crucial hereditary character. However, there may be no phenotypic similarities with the parents in many of these traits. This is due to their complex regulation, with an important genetic component, and the presence of important environmental factors that can influence the phenotypic outcome of a given trait.
Below, we explain 3 of the most studied and discussed personal traits: eye color, the appearance of the first period (menarche), and male pattern baldness. What role does genetics play in each of them?
What is the origin of my eye color?
The iris is the colored ring that surrounds the pupil, being in charge of contracting or dilating it depending on the amount of light that must enter the eyeball and reach the retina.
Its color is basically determined by the amount of melanin and its distribution within the first two layers of the iris: the epithelium and the stroma. If there is more of this pigment, the eye will be darker, while if there is less, it will be lighter.
Other factors also play a role in the final color of the eye, such as the relationship between the different forms of melanin (eumelanin and pheomelanin) and the ability of the extracellular components to scatter and absorb light. All this translates into the large number of different colors that people’s eyes present.
From a genetic point of view, the architecture of eye color is complex, with a highly polygenic inheritance, which means that many genes are involved in iris pigmentation.
Until recently, it was believed that eye color followed a simple Mendelian inheritance pattern. However, thanks mainly to the development of the GWAS methodology, more than 50 gene regions associated with this trait have been identified, with important associations of genes involved in pigmentation (such as the widely described HERC2) and in iris morphology and structure, among many others.
However, despite significant advances, studies to date have not yet been able to fully elucidate the role of genetics in determining eye color, with factors still undescribed. It is for this reason that, on occasion, the results obtained by DNA tests may not correspond to reality. The necessary future research will allow us to better understand the complex genetic architecture that determines iris color.
My friend got her period when she was 16, and I got mine when I was 10, why?
Menarche is the name given to the first menstruation in women. It typically occurs approximately two years after the onset of breast development and pubic hair and can occur prematurely before the age of 9 or delayed until the age of 16. It symbolizes a state of maturity characterized by the preparation of the female body for reproduction.
The age of onset of menstruation depends on several factors. Several studies have highlighted the importance of certain distinct environmental factors that may influence the onset of menarche, such as diet, physical activity, or birth weight. However, it appears that the genetic factor is the most important, with a heritability of the trait of up to 82%. Several studies have been carried out to date, having detected more than 150 genes involved, among which the LIN28B gene stands out, previously associated with an earlier onset of puberty and shorter stature.
Therefore, due to its important hereditary character, in many cases, knowing the age of menarche of the mother, it is possible to predict when the daughter is more likely to develop it, although, as we have said before, the environmental factor and genetic factors not identified to date can alter this prediction.
My father is bald, am I going to be bald too?
Hair is in constant renewal and hair loss is a completely normal process. There are 3 different phases in the hair renewal cycle: the growth phase, the resting phase, and the shedding phase.
When this renewal is exhausted in men, generally due to follicle degeneration, we speak of male baldness. This trait is strongly conditioned by genetics and male sex hormones: androgens.
Although hair growth is influenced by various hormones, the effect of androgens is the most important, as they are responsible for hair growth and can stimulate or even inhibit hair growth depending on the location of the body.
At the genetic level, to date, hundreds of genes related to male baldness have been identified, many of them associated with androgen biology. Of these, the most important, responsible for 11% of the heritability of the trait, are found on the X chromosome, which men inherit directly from their mothers. However, there are hundreds of associated variants scattered throughout the genome that we inherit from both parents, so it is difficult to predict whether a man will be bald just by knowing that his father is bald.
These three genetic personality traits exemplify how scientific advances using increasingly complex computational techniques and robust studies are uncovering what lies behind each trait.
In addition, they shed light on the important environmental factor, which can be a determining factor in the expression of a certain phenotype, sometimes with an even greater influence than the individual’s own genetics.
Do you want to know what your DNA says about these traits? You can access this information, and much more, with our DNA test.