DNA and Inheritance

The process by which genetic information is passed to us from our parents is called heredity. This determines our inherited characteristics, such as hair colour, eye colour or blood group.

To understand how genetic information is passed on, let’s look at cells.

If you zoom in on a cell, you can identify the nucleus, which controls all the activity in the cell. It contains genetic information, also known as DNA.


DNA stands for deoxyribonucleic acid. It is a molecule that contains the information that determines all of our inherited characteristics. Our DNA is arranged in chromosomes, which are structures within the nucleus.

In humans, we have 23 pairs of chromosomes in each cell, which means 46 individual chromosomes. Each parent contributes one chromosome to each pair, which means that the offspring inherits half of their chromosomes from their mother and the other half from their father.

Polymers are really long molecules that are made up of smaller molecules linked together. DNA is a type of polymer and if we were to unravel the chromosomes, we would see long strands of DNA. The DNA molecule consists of two long strands that wind around each other to form a shape known as a double helix. The two strands are held together by bonds between base pairs.

There are four types of bases in DNA:

  • Adenine (A)
  • Cytosine (C)
  • Guanine (G)
  • Thymine (T)

Adenine always pairs with thymine and cytosine always pairs with guanine. Each pair of bases is held together by weak hydrogen bonds.

Genes and the Genome

A gene is a section of DNA that codes for a particular characteristic. Alleles are different forms of a gene, and one is inherited from each parent.

However, this is just a simple diagram. In reality, there might be many genes that code for a characteristic, which interact together. Just like chromosomes, genes also come in pairs. So, how the two genes in each pair interact will determine your characteristics.

The genome is the complete set of genetic instructions found in an organism. It is made up of all the genes in an organism. Each organism has a unique genome and it is what makes each individual different from one another.

Understanding the genome is important because it can provide insights into how organisms develop and function.

The Discovery of DNA

The discovery of DNA is an important milestone in the field of genetics and biology. In the 1950s, James Watson and Francis Crick made a major discovery about DNA when they figured out its structure. They showed that DNA is a double helix, made up of two strands. This discovery was very important because it helped scientists understand how genetic information is stored and passed on.

Before Watson and Crick’s discovery, scientists knew that DNA played a role in genetics, but they didn’t know how it worked. The work of Rosalind Franklin and Maurice Wilkins also helped Watson and Crick understand DNA’s structure. Franklin made clearer X-ray patterns of DNA molecules, and Wilkins shared his own research with Watson and Crick. Together, their work allowed Watson and Crick to build a model of DNA’s structure that is still used today.

You’ve used 0 of your 10 free revision notes for the month

Sign up to get unlimited access to revision notes, quizzes, audio lessons and more

Sign up