Genetic Recombination - Definition, Types and Examples | Biology Dictionary (original) (raw)

Genetic Recombination Definition

Genetic recombination occurs when genetic material is exchanged between two different chromosomes or between different regions within the same chromosome. We can observe it in both eukaryotes (like animals and plants) and prokaryotes (like archaea and bacteria). Keep in mind that in most cases, in order for an exchange to occur, the sequences containing the swapped regions have to be homologous, or similar, to some degree.

The process occurs naturally and can also be carried out in the lab. Recombination increases the genetic diversity in sexually reproducing organisms and can allow an organism to function in new ways.

Examples of Genetic Recombination

Part of Your Making

Genetic recombination occurs naturally in meiosis. Meiosis is the process of cell division that occurs in eukaryotes, such as humans and other mammals, to produce offspring. In this case, it involves crossing-over. What happens is that two chromosomes, one from each parent, pair up with each other. Next, a segment from one crosses over, or overlaps, a segment of the other. This allows for the swapping of some of their material, as you can see in the illustration below. What we end up with is a new combination of genes that didn’t exist before and is not identical to either parent’s genetic information. Note that recombination is also observed in mitosis, but it doesn’t occur as often in mitosis as it does in meiosis.

Natural Self-Healing

The cell also can also undergo recombinational repair, for example, if it notices that there is a harmful break in the DNA: the kind of break that occurs in both strands. What we observe is an exchange between the broken DNA and a homologous region of DNA that will fill the gaps. There are also other ways that recombination is used to repair DNA.

Functions of Genetic Recombination

We’ve already covered some the consequences of genetic recombination, but in this section we will discuss Recombinant DNA Technology. This is a relatively new technology that is allowing scientists to change genes and organisms by manipulating DNA. What makes this so important is the fact that it has improved our understanding of diseases and, consequently, has expanded our ways of fighting them.

As you might expect, DNA segments are joined together in this Technology. For example, a gene can be cut out from a human and introduced into the DNA of a bacterium. The bacterium will then be able to produce human protein that is otherwise only made by humans. The same thing is done in gene therapy. Let’s assume a person is born without a particular essential gene, and is suffering from an illness due to the absence of that gene. Scientists can now introduce the missing gene into that person’s genome by using a virus that infects humans. First, they join the needed gene with the virus’s DNA and then they expose the person to that virus. Since all viruses blend their DNA with their host’s DNA, the gene that is added by the scientists ends up being part of the person’s genome.

Types of Genetic Recombination

Scientists have observed the following types of recombination in nature:

• • Homologous (general) recombination: As the name implies, this type occurs between DNA molecules of similar sequences. Our cells carry out general recombination during meiosis.
• • Nonhomologous (illegitimate) recombination: Again, the name is self-explanatory. This type occurs between DNA molecules that are not necessarily similar. Often, there will be a degree of similarity between the sequences, but it’s not as obvious as it would be in homologous recombinations.
• • Site-specific recombination: This is observed between particular, very short, sequences, usually containing similarities.
• Mitotic recombination: This doesn’t actually happen during mitosis, but during interphase, which is the resting phase between mitotic divisions. The process is similar to that in meiotic recombination, and has its possible advantages, but it’s usually harmful and can result in tumors. This type of recombination is increased when cells are exposed to radiation.

Prokaryotic cells can undergo recombination through one of these three processes:

• • Conjugation is where genes are donated from one organism to another after they have been in contact. At any point, the contact is lost and the genes that were donated to the recipient replace their equivalents in its chromosome. What the offspring ends up having is a mix of traits from different strains of bacteria.
• • Transformation: This is where the organism acquires new genes by taking up naked DNA from its surroundings. The source of the free DNA is another bacterium that has died, and therefore its DNA was released to the environment.
• Transduction is gene transfer that is mediated by viruses. Viruses called bacteriophages attack bacteria and carry the genes from one bacterium to another.
• Gene – A sequence of nucleotides on a chromosome. Genes are passed on from parents to offspring and are the determinants of an organism’s traits.
• Genome – The complete set of genes that belongs to an organism or a cell. Each human cell containing a nucleus has a copy of the person’s entire genome.
• Homology – Similarity of the structure, origin, or position of two or more structures, regardless of their functions.
• Meiosis – A process of cell division that results in daughter cells containing half the amount of chromosomes that the parent cells contained.

Quiz

1. Recombination decreases the genetic diversity within a species.
A. True
B. False

Answer to Question #1

False. Genetic recombination increases genetic diversity by producing new combinations of genes.

2. Genetic recombination in the process of meiosis involves:
A. Jumping
B. Crossing-over
C. Crawling
D. Repair

Answer to Question #2

B is correct. Crossing over is what results in the exchange of DNA between chromosomes during meiosis.

3. Which of the following is not a form of genetic recombination that occurs in prokaryotes?
A. Transformation
B. Integration
C. Conjugation
D. Transduction

Answer to Question #3

B is correct. Transformation, conjugation, and transduction are the forms of recombination that occur in prokaryotes.