Difference Between Linkage and Crossing Over

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Linkage and crossing over are two related, yet different phenomena occurring in eukaryotic organisms. Genetic linkage or, simply, the linkage is the tendency of genes to stay together in a chromosome while crossing over is a phenomenon through which genetic information is exchanged in the germline. Both of these play an important role in heredity. Both the events are somewhat related to each other. However, Linkage is more about the tendency of genes in a chromosome to inherit together. Through crossing over, the genes separate and segregate into different gametes.

We will learn more about genetic linkage and crossing over and the differences between them in this article.


Genetic Linkage

As explained above, genetic linkage means the tendency of the genes or DNA sequences on a chromosome to be inherited together during meiosis of sexual reproduction. Linked genes are the ones located on the same chromosome. For example, genes on hair colour and eye colour. That is why some individuals inherit hair and eye colours together. Such as black hair with brown eyes or individuals with brown hair and blue eyes inherited from parents.


Crossing Over

The exchange of chromosomes between non-sister chromatids to form gametes is crossing over. Crossing over shuffles the alleles on parental chromosomes, so that the gametes carry the combination of genes from mother and father. In simple language, it is the swapping of genetic material in the germline. During meiosis, or formation of an egg cell and sperm cells, paired chromosomes get aligned so that similar DNA sequences from the paired chromosomes come against one another. This phenomenon accounts for genetic variation in sexually reproducing organisms and it is also essential for normal segregation of chromosomes.


The Difference Between Linkage and Crossing Over

  • Crossing over is the process of separation of genes between homologous pairs into various gametes. Linkage is the tendency of inheriting genes together on the same chromosome.

  • Linkage occurs when two genes are closer to each other on the same chromosome. On the other hand, crossing over takes place when two genes are located far apart on the same chromosome.

  • Crossing over may disrupt the gene groups made by linkage.

  • Unlike the linkage, crossing over only occurs during the prophase of meiosis I and it produces recombinant alleles, which is not the case in the linkage.

Linkage

Crossing Over

Ensures that the genes stay in a chromosome to inherit together

Crossing over enables the separation of genes in a chromosome and separates it into various gametes

The strength of the genetic linkage between two genes is thought to be inversely proportional to the distance between them in the chromosome

The probability of two genes crossing over is directly proportional to the distance between them in the chromosome

The strength of the linkage between two genes can increase if the distance between them decreases

The probability of two genes crossing over decreases if the distance between them decreases

Ensures the continuity of the parental trait in the offspring

Causes alterations in the parental traits in the offspring

Reduces the probability of variation through sexual reproduction

Increases the probability of introducing variability in sexual reproduction

FAQ (Frequently Asked Questions)

1. What is Linkage and What Are Its Two Faces?

Genetic linkage means the tendency of the genes or DNA sequences on a chromosome to be inherited together during meiosis of sexual reproduction. Linked genes are the ones located on the same chromosome. The two faces of linkage are coupling and repulsion.

2. What is Crossing Over?

The exchange of chromosomes between non-sister chromatids to form gametes is crossing over. Crossing over shuffles the alleles on parental chromosomes, so that the gametes carry the combination of genes from mother and father. In simple language, it is the swapping of genetic material in the germline.

3. What is the Basic Difference Between Crossing Over and Linkage?

Crossing over is the process of separation of genes between homologous pairs into various gametes. Linkage is the tendency of inheriting genes together on the same chromosome. 

4. How Are Crossing Over and Linkage the Two Events of Heredity Related to Each Other?

Linked genes are the ones that are located on the same chromosome. Alleles of these genes tend to segregate together during the meiosis phase unless they are separated by the process of crossing over. When two homologous chromosomes exchange genetic material, it is called crossing over. The closer the genes are on a chromosome, less likely it is for them to get separated during crossing over.

5. Why Didn’t Mendel Recognise the Phenomenon of Linkage During His Experiments?

Mendel performed early experiments on pea plants to establish the concept of genes and heredity and from the conclusions of his experiments, he postulated three laws of inheritance The law of segregation, the law of dominance and the law of independent assortment. However, Mendel could not recognise genetic linkage through his experiments because the characteristics Mendel studied were located on different chromosomes.

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