Differentiate between linked genes and unlinked genes?

Genes are specific sequences of DNA that code for proteins and determine traits in an organism. During the study of chromosomal theory of  inheritance, scientists found that not all genes behave the same way. Some genes tend to be inherited together while others assort independently. Based on this behavior, genes are divided into two types: linked genes and unlinked genes. This concept is very important in genetics because it helps in understanding how traits are passed on and how gene positions can be mapped on chromosomes. These differences are explained based on specific criteria:

1. Based on Chromosomal Location

Linked genes are located close to each other on the same chromosome. Because of their close physical proximity, they usually move together during meiosis and are inherited as a group. For example: In Drosophila melanogaster (fruit fly), the genes for eye color and wing shape are located close to each other on the X chromosome.

Unlinked genes are either located on different chromosomes or are far apart on the same chromosome. Their distance is so great that crossing over happens frequently, making them behave as if they are on separate chromosomes.

2. Based on Inheritance Pattern

Linked genes do not follow Mendel's law of independent assortment. They are inherited together more often than not, unless crossing over occurs between them.

Unlinked genes follow Mendel's law of independent assortment and are passed to offspring independently of each other.

3. Based on Recombination Frequency

Linked genes show recombination frequency less than 50%. The closer the genes are on a chromosome, the lower the chance of crossing over between them. This helps in estimating the distance between them.

Unlinked genes show 50% recombination frequency. Crossing over between them occurs so often that it appears as if the genes are assorting randomly.

4. Based on Use in Gene Mapping

Linked genes are very important in gene mapping. The recombination frequency between them helps scientists to construct linkage maps. The lesser the frequency, the closer the genes are on the chromosome.

Unlinked genes do not help in determining distance between each other as their independent assortment gives no specific information about gene location.

5. Based on Historical Observations

Linked genes were first discovered by Bateson and Punnett in 1905 while studying flower color and pollen shape in Lathyrus odoratus (sweet pea). They observed that some traits did not follow expected Mendelian ratios and concluded that certain genes were linked.

Unlinked genes were explained by Gregor Mendel during his experiments with pea plants. He worked with genes located on different chromosomes and observed independent assortment of traits like seed color and seed shape.






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