Transmitted from parent to child, it is contained in genes carried by chromosomes in the nucleus.
We inherit our DNA and our genes from our parents. Half of our DNA comes from the mother, and the other half of our DNA comes from the father.
By knowing what types of genes two parents have, we can predict the likelihood that the children will inherit certain characteristics. This is useful when parents know that they may carry a genetic condition.
Let’s look at our DNA which is organized into chromosomes. You can also tell that these chromosomes come in pairs. One chromosome in each pair came from the mother, the other from the father.
Chromosomes and genes
A gene is a section of DNA that carries the code for a particular protein. Different genes control the development of different characteristics of an organism.
Many genes are needed to carry all the genetic information of a complete organism. Chromosomes, which are found in the cell nucleus, contain many genes.
The number of genes and chromosomes varies from one species to another. For example, cells in humans have 46 chromosomes that carry approximately 30,000 genes in each cell; and cells in fruit flies have eight chromosomes that carry approximately 13,600 genes.
Uses of genetic information
In a sense, almost all information about health and fitness can be called ‘genetic information’. A casual glance reveals information about a person’s gender, race, height, weight, and characteristics of two people that are related, in whole or in part, to inherited genetics.
Doctors and insurers have been using general family medical records for more than 100 years to make inferences about the present and future health of individuals.
Doctors and healthcare professionals were making clinical observations on genetic conditions long before technology was developed to directly test for such conditions.
Similarly, information that a person has high blood pressure , high cholesterol levels, diabetes, or cancer can also provide information about that person’s genetic heritage.
Plants can be cloned artificially by cuttings or tissue culture. Animals can be cloned using embryo transplants or fusion cell cloning. Genetic information from one species can be transferred to another species through genetic engineering.
Sequence of genetic information
The genetic information of an organism is stored in DNA molecules.
How can one type of molecule contain all the instructions to make complicated living things like us?
What component or characteristic of DNA can contain this information?
It has to come from the nitrogen bases, because, as you know, the backbone of all DNA molecules is the same.
But there are only four bases in DNA: G, A, C, and T. The sequence of these four bases can provide all the instructions necessary to build any living organism.
It can be difficult to imagine that 4 different “letters” could communicate so much information. But think of the English language, which can represent a large amount of information using only 26 letters.
Even deeper is the binary code used to write computer programs. This code contains only ones and zeros, and think of all the things your computer can do.
The DNA alphabet can encode very complex instructions using just four letters, although the messages end up being very long. For example, the bacterium E. coli carries its genetic instructions in a DNA molecule that contains more than five million nucleotides.
The human genome (all the DNA in an organism) consists of around three billion nucleotides divided between 23 paired DNA molecules or chromosomes.
The information stored in the order of the bases is organized in genes: each gene contains information to make a functional product. The genetic information is first copied to another nucleic acid polymer, RNA (ribonucleic acid), preserving the order of the nucleotide bases.
Genes that contain instructions for making proteins are converted into messenger RNA (mRNA). Some specialized genes contain instructions for making functional RNA molecules that do not make proteins.
These RNA molecules work by affecting cellular processes directly; for example, some of these RNA molecules regulate mRNA expression.
Other genes produce RNA molecules that are required for protein synthesis, transfer RNA (tRNA) and ribosomal RNA (rRNA).
For DNA to function effectively in storing information, two key processes are required. First, the information stored in the DNA molecule must be copied, with minimal errors, each time a cell divides.
This ensures that both daughter cells inherit the full set of genetic information from the parent cell. Second, the information stored in the DNA molecule must be translated or expressed.
For stored information to be useful, cells must be able to access instructions for making specific proteins so that the right proteins are made in the right place at the right time.
Both the copying and reading of information stored in DNA depend on the base pairing between two nucleic acid polymer chains. Remember that the structure of DNA is a double helix.
The sugar deoxyribose with the phosphate group forms the scaffold or backbone of the molecule. The bases point inwards. The complementary bases form hydrogen bonds with each other within the double helix.
See how the larger bases (purines) pair up with the smaller ones (pyrimidines). This keeps the width of the double helix constant. More specifically, A pairs with the pairs T and C with G.
As we discuss DNA function in later sections, keep in mind that there is a chemical reason for specific base pairing.
To illustrate the connection between information in DNA and an observable characteristic of an organism, let’s consider a gene that provides the instructions for building the hormone insulin.
Insulin is responsible for regulating blood sugar levels. The insulin gene contains instructions for assembling insulin from individual amino acids.
Changing the nucleotide sequence in the DNA molecule can change the amino acids in the final protein, leading to a malfunction of the protein. If insulin is not working properly, it may not be able to bind to another protein (insulin receptor).
At the organismal level of organization, this molecular event (DNA sequence change) can lead to a disease state, in this case, diabetes.