Have you ever looked at a child and felt an overwhelming sense of familiarity, as though you somehow recognize the face, but not the child to whom it belongs? Later, has it ever turned out to be the child of a couple you know? If this hasn’t happened, then perhaps you have remarked about the striking resemblance of a child to their father or mother? On the other hand, however, sometimes you see two children from the same couple that look utterly different from one another.
This begs the question: how can two children from the same parents look so different?
Meet the Chromosomes
The journey of a child from being an embryo to a full-grown baby is quite amazing in and of itself. It all starts when sperm from a male meets the egg in the ovaries of a female. The fusion results in the formation of an embryo, and this embryo, after going through various stages of development over the course of nine months, becomes a baby.
The Packets of Personality
Every human being has a set of chromosomes. If you are hearing this term for the first time, then there are a few things you should know. Basically, a chromosome is a package that contains the majority of the DNA in a living being.
Now, before this concepts confuses you any further, just remember that DNA (Deoxyribonucleic acid) is a molecule that carries most of the genetic instructions used in the reproduction and development of human beings. In short, if you’re a fetus, then chromosomes are the packages that carry information about how you’re going to be once you are born.
If you look at an image of a chromosome, it looks like an ‘X’ in the English alphabet. This ‘X’ is actually formed by the combination of two separate halves; one comes from the mother and the other from the father. Essentially, each chromosome contains a set of genes, and each chromosome contains two copies of every gene (one from the mother and one from the father). The one gene that is more dominant is expressed in the features of the baby.
Mix and Match
There are just 23 pairs of chromosomes, but almost 20,000 genes strung on these chromosomes. Parents don’t pass genes to their offspring, they pass chromosomes. Every cell in a father contains a set of genes that are exactly alike. The same thing is true with every mother. In fact, they got these genes from their own parents (through their chromosomes).
While making a sperm cell, half of the X-shaped chromosomes are added to the mix, which decides half the set of genes in the child. Similarly half of the mother’s chromosomes are contributed which decides the other half set of child’s genes. Hence the child gets new chromosomes, the genes in which contain a mix of both their father’s and mother’s genes.
Note that there is no specific protocol that is followed while loading a sperm cell or an egg with chromosomes; instead, nature randomly picks chromosomes from the bodies of the father (or the bodies of grandparents). The same thing happens with the mother’s chromosomal contribution!
Before trying to puzzle out this problem any further, try looking at it this way. Your physical features are decided by a random mix-and-match of the genes from your four grandparents (two from the father’s side and two from the mother’s). This is the reason that siblings from the same parents can sometimes look so dissimilar, because the set of genes in one person can be immensely different from the other, despite having the same parents.
Role of the environment
It’s not just the genes that shape your physical personality, environmental factors also play a significant role. In genetic language, ‘environment’ means the conditions in which you grow, the foods that you eat, the level of physical activities you engage in; all these affect how you are going to look as you grow old. Since the environment of your siblings can be quite different from yours, therefore they can look very different from you.
Nature has its own way of selective, yet random, choosing of the genes that shape your personality and the environment that plays a vital role in your upbringing; this is why there’s no point in fretting about how different you may look from your sibling!