The close relationship of genes or other DNA sequences on the same chromosome is known as linkage. The closer two genes are to each other on the chromosome, the more likely they are to be passed down from parent to child.

And the closer genes are on a chromosome, the more chance of detecting this linkage is more likely to be passed together from grandparents, parents, and offspring because there are fewer recombinations between these genes during meiosis.

Recombination

Breaking and recombining segments of DNA to form new allele combinations is known as recombination. Genetic variety at the gene level originates from this recombination process. It reflects differences in DNA sequences between species.

The test cross progeny's recombination frequency is never greater than 50%. As a result, if two genes are completely linked, the chance of recombination is nearly nil.

Differences and Types

There are two types of Linkages:

Complete Linkage

Due to the lack of crossing over, genes on the same chromosome do not split and are inherited together over generations.

The ability to inherit a combination of parental features is enabled by complete linkage. Although it is uncommon, it has been observed in male Drosophila and other heterogametic creatures.

Incomplete Linkage

Due to crossing over, genes on the same chromosome have a propensity to split, resulting in recombinant progeny that differs from the parental type.

In autonomous assortment, the number of recombinant individuals is frequently lower than expected. Each of the four types (two parental types and two recombinant types) has a 25% chance of being selected in an independent assortment.

In the event of linkage, each of the two parental types has a percentage of more than 25%, while each of the recombinant kind has a percentage of less than 25%.

Types of Genetic Recombination

There are three types of Recombination:

Homologous Recombination

This type arises between DNA molecules with comparable sequences, as the name implies. During meiosis, the cells undergo widespread recombination.

Nonhomologous Recombination

This form of interaction happens between DNA molecules that aren't necessarily related. There will often be some degree of sequence similarity, but it will not be as clear as it would be in homologous recombinations.

Site-specific Recombination

This can be seen between specific, extremely short sequences that are frequently similar.

Differences between Linkage and Recombination

Linkage	Recombination
It happens when two genes are very close to one another.	It occurs when two genes are relatively far apart.
Two different genes at different loci (single: locus) do not separate and are passed down to the next generation.	Recombined genes are changed versions of parental genes that are inherited from two separate genes at different loci of homologous or non-homologous chromosomes.
The linkage between two genes weakens as the distance between them grows, and recombination through crossing over becomes more common.	When the distance between two points diminishes, the likelihood of recombination lowers as well.
The inheritance of the same parental features for more than two generations is known as linkage.	Recombination is the variation of parental qualities in the next generation to exhibit non-parental traits.
It does not support the law of independent assortment.	It supports the law of independent assortment.
Two or more linked genes are usually inherited in the same combination for more than two generations in linkage.	Recombination is the exchange of genetic material between distinct organisms (in the case of sexual reproduction, between male and female), resulting in the development of offspring with a combination of features.

Differences Between Linkage and Crossing Over

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We hope that the difference between linkage and crossing over is very much clear. The next section talks about an important experiment that led to a transition in the field of genetics.

Did You Know About Morgan’s Experiment?

Thomas Hunt Morgan experimented in 1910 at Columbia University. Morgan’s experiment aimed at proving the fact that sexual reproduction produces variations in the off-springs. For experimenting, Morgan started breeding fruit flies (Drosophila). In his experiment, he found that among thousands of red-eyed fruit flies, there was one fly with white-eye and that too, a male fly. After several observations, Morgan inferred that:

Eye color and sex were determined by the same chromosome and thus, chromosomes carry the genes for the inheritance of parental traits in the offspring.

Morgan’s experiment was published in an article, titled “Sex Limited Inheritance in Drosophila”.

Fruit flies were the best alternative for Morgan’s experiment because of the following reasons:

Males and females could be easily differentiable.

Fruit-flies had a short lifespan i.e. 2 weeks.

Many off-springs could be produced by a single mating.

They were easy to cultivate.

Males and females could be easily differentiated.

Thomas Hunt Morgan's experiment also noticed that the white-colored eyes were only present in males. The reason behind this was that the white-colored trait was found only on their X-chromosome and thus, proved that the inheritance of traits can differ by sexes. Females didn’t show white eyes because it was only present on one of their X-chromosome. Thus, Morgan’s experiment was the perfect explanation of linkage and crossing over.

Types of Linkages

Let’s get to the next topic of the discussion, what are the different types of linkages in the genetic inheritance proposed by the Morgan linkage experiment.

So, there are two types of linkages:

Complete Linkage

Complete linkage is a type of linkage where two or more traits are inherited and are visible in two or more further generations. These types of linkages are found together in the chromosomes of the same type.

Incomplete Linkages

Incomplete linkages produce some portion of non-parental combinations. These types of linkages are found at a distance and result in occasional destruction of chromosomal segments while crossing over.

We hope that the concept of types of linkages is very much clear. We’ll be heading towards our next section.

There Are 3 Types of Recombination

Homologous Recombination:

Homologous recombination is one of the types of recombinations where nucleotide sequences are interchanged two identical nucleic acids (DNA/ RNA)

Non-Homologous Recombination:

Non-homologous recombination is a type of recombination by which chromosomal double-strand breaks in the DNA of somatic cells get repaired.

Site-Specific Recombination:

Site-specific recombination is a type of recombination where DNA strands interchange DNA strands among the segments having a certain degree of homology.

We hope that we were able to explain linkage and combination, types of linkage mechanisms, and types of genetic recombinations. Now, we are heading towards our final topic of the discussion i.e. recombination of linked genes.

Recombination of Linked Genes

This is the final topic of the discussion. We will understand the recombination of the linked genes with an example.

The character traits of blonde hair and patchy skin appear on a person because both of these attributes are present in the same chromosome. Homologous recombination leads to a rare splitting of two genes.

The chance of inheritance of the two mentioned attributes is very low in homologous recombination. As a result, most of these traits are inherited at the same time.

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