Do you hate it when people say, “Wow, you look like your mom”? Have you ever wondered why? It all starts with genetics. Genetics is the science of heredity. Geneticists do research to understand how traits like hair color, eye color and even nose shape are passed on from parents to their children.
For centuries, people have noticed that children, animals and other offspring inherited certain traits from their parents. Long ago, the philosopher Aristotle (who was a student of Plato) believed that traits were controlled by liquid factors in our blood. If a substance from a mother and father blended together, that was how the traits were combined and passed to their child. An example would be one parent having very fair skin and the other having dark skin, and then the child having medium skin.
The three main parts of heredity are DNA, genes and chromosomes. DNA, or deoxyribonucleic acid, is found in the center of every cell in the human body. DNA helps the production of proteins that help with growth, repair, replacement and reproduction of cells. Every person’s DNA is different except for identical siblings; they have the same DNA. The first model of DNA was made in 1953 by Francis Crick and James Watson. The two scientists also had help from another scientist, Maurice Wilkins. Wilkins realized that X-rays could play a part in viewing DNA. The model showed that DNA is shaped like a ladder, called a double helix. The “ladders” are made from deoxyribose sugar, phosphates and molecules called bases. The four bases are thymine, adenine, guanine and cytosine.
A gene is a segment of DNA that contains instructions for making certain protein. On average, a person has 22,500 genes. These genes determine what traits a person will have. When a cell needs a certain protein, it just copies the gene that is needed. This copy is made from another acid called RNA (ribonucleic acid).
There are two different kinds of traits: dominant and recessive. Dominant traits are referring to a gene or trait that is always observable. Recessive traits are traits referring to a gene or trait that is passed on, but not observable when a dominant gene is present. Recessive traits also tend to skip over a generation or two, meaning that if your dad has brown eyes and your mom has green eyes and you have brown eyes, that means you got your eyes from your dad because brown eyes are dominant and green are recessive. With me, I have brown eyes (which are dominant), blonde hair (which is recessive), straight hair (which is recessive) and dimples (which are dominant).
Genes are located on chromosomes. Chromosomes are structures found in a cell’s nucleus. Each chromosome can have up to several thousand genes lining it. Human chromosomes come in pairs. One member of each pair comes from the dad and then the other comes from the mom. There are a total of 46 chromosomes or 23 pairs in all. One pair of chromosomes determines whether the child will be male or female. Females have a pair of X chromosomes and males have one X and one Y chromosome.
So now, whenever someone says “Wow you look like you Mom,” you can give them the basics on why, and maybe even teach them something.