The Difference Between Linkage and Crossing Over
Genetics is a fascinating subject, and the different mechanisms that give rise to variability in offspring have been the subject of extensive research. Two such mechanisms are linkage and crossing over. These two concepts are related to how genes are distributed and segregated during meiosis, the process of cell division that leads to the production of gametes (sperm or eggs). In this article, we will explore the difference between linkage and crossing over.
What is Linkage?
Linkage refers to the physical proximity of two or more genes on the same chromosome. When genes are located close together on a chromosome, they tend to be inherited together as a unit, rather than independently. This is because during meiosis, the two chromosomes of a homologous pair may not always separate, and there is a chance that both chromosomes with the linked genes will be passed down to the same gamete. The phenomenon of linked genes is called linkage.
The degree of linkage between two genes is measured by the distance between them on the chromosome, in units called centimorgans (cM). The higher the distance between two genes, the lower the linkage, and the more likely they are to be separated during meiosis.
What is Crossing Over?
Crossing over is the exchange of genetic material between homologous chromosomes that occurs during prophase I of meiosis. During this stage, the homologous chromosomes pair up and exchange segments of DNA. This exchange occurs at specific points called chiasmata, which are formed when the chromosomes break and rejoin in a different pattern. Crossing over results in new combinations of alleles, which increases genetic diversity in offspring.
The likelihood of crossing over between two genes is related to the distance between them on the chromosome. Genes that are far apart are more likely to experience crossing over, while genes that are tightly linked are less likely to do so.
The Difference Between Linkage and Crossing Over
While both linkage and crossing over are related to how genes are inherited, they are not the same thing. Linkage refers to the physical proximity of genes on the same chromosome, while crossing over is the exchange of genetic material between homologous chromosomes. Linkage tends to result in the co-inheritance of linked genes, while crossing over results in new combinations of alleles.
In summary, linkage and crossing over are two important mechanisms that influence the inheritance of genes, and their effects can be seen in the diversity of the offspring. Understanding these mechanisms is crucial for genetic research, as well as for predicting and managing inherited diseases.
Table difference between linkage and crossing over
| Linkage | Crossing over | |
|---|---|---|
| Definition | When two or more genes are located on the same chromosome and tend to be inherited together. | The exchange of genetic material between homologous chromosomes during meiosis, resulting in the creation of new combinations of alleles. |
| Action | Reduces the number of possible genetic combinations between linked genes. | Increases the number of possible genetic combinations between genes that are not linked. |
| Result | Increases the likelihood that certain traits will be inherited together. | Creates new combinations of traits that were not present in the parents. |
| Frequency | Occurs when genes are located closely together on the same chromosome. | Occurs when homologous chromosomes exchange genetic material during meiosis. |
| Effect on genetic diversity | Reduces genetic diversity by limiting the number of possible combinations of alleles. | Increases genetic diversity by creating new combinations of alleles. |