As you have learned, there are several types of asexual reproduction, which involves an organism becoming two organisms. For example, a potato, which is a tuber, produces another potato by vegetative reproduction. In this type of asexual reproduction, a modified stem or root of the parent plant grows offspring that stay attached to it. But all of the different forms of asexual reproduction have a common result: a new organism that is genetically identical to its parent. What does it mean to be genetically identical? It means that the new offspring has the same DNA as its parent. Asexual reproduction by binary fission demonstrates this process clearly, as modeled in the illustration below of a bacterium becoming two bacteria.
An illustration shows four stages of the binary fission in bacteria.
Source: Amit John. Pearson India Education Services Pvt. Ltd
The first stage shows a cell with a DNA inside the nucleus. The second stage shows the two ends of the cell’s DNA going to opposite sides of the cell, and the cell starts to grow larger and develop more organelles and more cytoplasm. The third stage shows the cell starting to divide, and the DNA separates into two separate strands, one on each side of the cell. A membrane starts to form in the middle of the cell. The fourth stage shows the cell splitting in half producing two identical daughter cells.
For bacteria, binary fission occurs in four stages. In the first stage, the cell prepares to split in two. Its DNA uncoils and then replicates. In the second stage, the two ends of the cell’s DNA go to opposite sides of the cell, and the cell starts to grow larger and develop more organelles and more cytoplasm. In the third stage, the cell starts to divide, and the DNA separates into two separate strands, one on each side of the cell. A membrane starts to form in the middle of the cell. In the fourth and final stage, the cell splits in half, and the parent cell has produced two identical daughter cells.
Being genetically identical means that the offspring has the same DNA as its parent. In the context of asexual reproduction, this means that the genetic information of the parent organism is replicated and passed on to the offspring without any alteration or recombination. The offspring inherits all the genetic traits and characteristics of its parent, resulting in a clone or replica of the parent organism. This genetic similarity ensures that the offspring will have the same physical and physiological attributes as the parent.
During binary fission, the genetic material in the form of DNA replicates inside the cell, resulting in two identical copies of the DNA. These copies then move to opposite ends of the cell. As the cell grows larger and develops more organelles and cytoplasm, a membrane begins to form in the middle, separating the two copies of DNA. Finally, the cell splits in half, resulting in two new cells, known as daughter cells, that are genetically identical to the parent cell. This means that the DNA sequence of the daughter cells is exactly the same as that of the parent cell. This process ensures the transmission of the exact genetic information from one generation to the next without any variations or genetic recombination.
To understand what it means for organisms to be genetically identical, let's start by explaining what DNA is. DNA, or deoxyribonucleic acid, is a molecule that contains the genetic instructions used in the development and functioning of all known living organisms. It is often described as the "blueprint" or "code" of life.
DNA is made up of sequences of nucleotides, which are the building blocks of the molecule. Each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base. The four nitrogenous bases found in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). These bases pair with each other in a precise manner: A always pairs with T, and C always pairs with G. This pairing is known as base pairing.
When an organism reproduces sexually, it inherits half of its DNA from each parent, leading to genetic variation. However, in asexual reproduction, the offspring is created from a single parent and inherits its entire set of DNA. This results in the offspring being genetically identical to the parent.
In the case of binary fission in bacteria, the first stage involves DNA replication. The DNA strands within the cell uncoil and each strand serves as a template for the creation of a new complementary strand. This process ensures that each daughter cell will receive a complete copy of the parent cell's DNA.
During the third stage, the cell starts to divide, and the DNA separates into two separate strands, one on each side of the cell. A membrane begins to form in the middle of the cell, eventually dividing it into two separate cells during the fourth stage. These daughter cells are genetically identical to the parent cell because they each contain an exact copy of the parent cell's DNA.
In summary, genetic identity refers to the offspring having the same DNA sequence as its parent. Asexual reproduction, such as binary fission in bacteria, leads to genetic identity as the offspring receive a complete and identical copy of the parent's DNA.