Today, we will discuss ‘genetic linkage and recombination’ patterns of inheritance. All of us have close friends with whom we go out. We sit together, eat together, or go to a mall. Similarly, genes also tend to move along with the genes that are adjacent to them, while they are inherited. We call this ‘genetic linkage’. Sometimes all your friends may not be grouped together, like when being chosen for debate teams. You may have to pair up with other classmates as well. Recombination of genes also shows a similar scenario. Like most sexually reproducing organisms, humans have 23 pairs of chromosomes in each cell. Genes are segments of DNA arranged along a chromosome. There’s a lot more genes than chromosomes; they have 19,000 genes on 23 chromosomes. Each gene isn’t going to get its own chromosome, so the genes line up tightly in a row on each According to Mendel’s ‘Law of Independent Assortment’, genes are independently inherited by the next generation and wouldn’t be affected by the inheritance of any other gene. He illustrated this law by crossing two pure-breeding pea plants of differing colour and shape and discovered four different offspring from the original genetic pair. Where the genes are placed on the chromosome is important. Let’s understand recombination first. When genes are on different sets of chromosomes, they are independent and do not influence one another, but in case of homologous chromosomes, they are likely to be exchanged between the non-sister chromatids during crossing over, resulting in recombinant chromosomes. Similarly, chances of recombination are greater between distant genes, and these genes are not inherited together. But adjacent genes, due to fewer recombination sites are inherited together. This is called ‘genetic linkage’ and such genes are ‘linked genes’. Based on these concepts, the distance between the genes and their recombination frequency can be determined along with a gene map. When 2 genes have traits that are often inherited together, we can say that the two genes are closely located and vice versa as well. The recombination frequency can be determined using the formula: ... Recombination frequency is represented as a percentage, 17 and it has a direct relationship with the distance between the genes. The RF of 1 % is equated to 1 centimorgan or 1 map unit. If the recombination frequency is more than 50 %, then the genes are considered ‘unlinked’ and they are likely to be assorted independently. Determining the recombination frequency for all the genes helps to map the whole genome of an organism Although the chances of recombination in closely located genes are significantly low, the possibility can not be ruled out. Sometimes the crossing over may also occur between genes that are closely located. But the likelihood of such recombination is extremely low due to very few sites of crossing-over. As a result, the degree of randomness for recombination will also be significantly low. If the total of different recombinants is 45 among 1000 offspring, then the recombination frequency would be: Here, the recombination frequency is very low. So, it can be said that the genes are close and are 4.5 Centimorgans or 4.5 map units apart. Similarly, if the RF is 37.5% then the genes are 37.5 CMs or 37.5 map units apart. In this video, we have learned that genes that are closely located are likely to be inherited together due to linkage. Only distantly located genes follow Mendel’s law of independent assortment. Recombination of genes happens due to the crossing-over of paired homologous chromosomes.