DNA and heredity biology lesson for kids

DNA and heredity biology lesson for kids: 1st, 2nd, 3rd, 4th, 5th, 6th and 7th grades biology lesson.


DNA is a very big molecule that has a code that determines pretty much everything about an organism. In many organisms, including humans, DNA is kept safe in the nucleus (plural: nuclei) of most the cell. Your eye color, skin color, height, and even how your organs work are all written in your DNA, and your cells read this code to do all their jobs.  
Every strand of DNA is a chain of four types of much smaller molecules. Scientists gave every one of the four types a letter to make them easier to remember: T, C, A, and G. To keep the code safe, every molecule of DNA is a double-helix; that means it has two long strands that curl around each other. Every one of the smaller molecules in the chain pairs up with specific partner on the other chain: T with C and A with G.
DNA strands are made up of stretches of code called genes. In humans, these genes can have anywhere from just a few hundred to more than 2 million individual letters! Human cells also have 23 pairs of DNA molecules in their cell nuclei, which means a total of 46. Of every pair, one DNA sequence came from your mother, and the other came from your father. That means that you have two copies of every gene you have, one on each of the molecules in this pair.
Having two copies of every gene is an important concept in heredity, the passing down of genes from parent to child. These two copies could be exactly the same, but they might be different. How they interact controls how your body works. A copy of a gene can be: dominant, which means it overpowers the other copy; recessive, which means the other copy overpowers it, or codominant, which means it is just as strong as the other copy. A good example of how this works is in your blood type.
There are four blood type genes that we will talk about here: A, B, and O. A and B dominate O. That means that if you have one A copy and one O copy, you will have blood type A. The same is true if you have a B copy and an O copy; your blood type will be B because of the B copy. If you have two identical copies of the gene (two As, two Bs, or two Os), though, you will have that blood type (A, B, or O, respectively) because both copies are exactly the same. It gets even more interesting if you have one copy of A and one of B. A and B are codominant with each other, so your blood type will be AB.
This table demonstrates the concept:

Possible Gene Combinations

Blood Type

A and A


A and O


B and B


B and O


A and B


O and O


This means that you can tell if somebody is related to you by looking at their blood! A parent with blood type O can never have a child with blood type AB because they don’t have an A or B gene to give to their children. Doctors and other scientists use this kind of information to help with medical treatments, like knowing the chances of a baby having a hereditary disease.

DNA is a really useful molecule, isn’t it?
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