Linkage and crossing over are biological events that occur during the meiosis cycle of sexual reproduction in eukaryotic organisms. Each of the genetic events leads to the offspring inheriting a distinct set of chromosome pairs. Notably, George Mendel’s Law of Independent Assortment does not apply to genetic linkage or linkage. The law said that each feature is acquired independently of other traits, although expectations were discovered quickly after his works were rediscovered. While Frans Alfons Janssens discovered chromosomal crossover or crossing over in 1909, Thomas Morgan developed the hypothesis in his publication Mechanism of Mendelian Heredity (1915).
Genetic Linkage
Genetic linkage, or simply linkage, is the inclination of genes or DNA sequences in a chromosome to be acquired together during the meiosis phase of sexual reproduction. British geneticists were the first to notice this trend. They attempted to duplicate Mendel’s findings in terms of bloom colour (purple and red) and pollen grain shape (long and round). When they mated purebreds of purple flowers with long pollen and red flowers with round pollen, they got purple flowers with long pollen and red flowers with round pollen. Purple-coloured flowers with lengthy pollen were more common in progeny than expected. Similarly, crimson flowers with spherical pollen yielded comparable results. However, recombinant alleles of the traits in question were far less than Mendel’s Law of Independent Assortment predicted. The close proximity of the genes for such features on a chromosome led to the conclusion that they were connected.
Crossing over
Crossing over or chromosomal crossover occurs when genetic material is shared across non-sister chromatids of homologous chromosomes during sexual reproduction. Crossing over of genetic elements occurs frequently in matching regions of comparable chromosomes. Unlinked genetic markers are more likely to communicate information. Furthermore, as genes are separated further apart, the frequency of crossing rises, resulting in crossover. Genetic repair theory and bacterial transformation theory are two popular ideas that state the concept of such genetic occurrences. Damaged sections or broken strands of DNA are replaced during meiosis, according to genetic repair theories. The bacterial transformation theory, on the other hand, claims that meiosis developed from bacterial transformation to spread genetic diversity. Evidence suggests, however, that crossing over may have originated from bacterial transformation, which evolved from DNA repair, thus intertwining the processes.
Difference between linkage and crossing over
|
Linkage |
Crossing over |
|
Linkage guarantees that related genes on the same chromosome are passed down in the same family. |
Crossing over causes genes on the same chromosome to be separated and segregated into different gametes. |
|
The linkage of a pair of genes being inherited together is inversely proportional to their chromosome distance. |
The spacing between genes on the chromosome is directly proportional to their odds of being segregated into separate gametes. |
|
As the distance between two genes reduces, the linkage strength between them increases. |
As the distance between two genes grows, the likelihood of chromosomal crossing increases |
|
The linkage strength, on the other hand, decreases as the genes are separated. |
The occurrence, on the other hand, diminishes as the genes get closer together. |
|
The parental traits are passed down to the progenies due to linkage. |
The paternal traits alternate in the progenies due to chromosomal crossover |
|
It minimises the linkage of a progeny’s attributes differing from their parents during sexual reproduction. |
Gene segregation could lead to trait alternation or the emergence of new traits in the future. |
Conclusion
The tendency for alleles to inherit together on the same chromosome is known as linkage. The degree of linkage is inversely proportional to the distance between the genes. Crossing over, on the other hand, is the tendency for genes on the same chromosome to split into multiple gametes. It causes genetic recombination, which results in genetic variety. The influence of each method on genes on the same chromosome is the key distinction between linkage and crossing over.