Difference Between Linkage and Crossing Over

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Difference Between Linkage and Crossing Over for NEET

NEET is an all-India pre-Medical Exam conducted by NTA (National Testing Agency) annually for admission in undergraduate Medical colleges. With the ease of accessibility of resources, the level of competitiveness has increased many folds.


To help the students level up their preparation the experts at Vedantu have compiled a set of authentic study material specially designed for the benefits of the NEET aspirants. In this article, we will learn the following concept of Linkage and Crossing Over. 


Table of Content - 

  • Linkage and Crossing Over - An introduction 

  • Genetic Linkage

  • Crossing Over 

  • Difference between Linkage and Crossing Over 

  • Tips for preparation 

  • Frequently Asked Questions 


Introduction

Linkage and Crossing Over are two related, yet different phenomena occurring in Eukaryotic Organisms. Genetic Linkage or, simply, 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.


Genetic Linkage

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 the 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 the 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


Tips for preparation - 

To boost your level of preparation for the NEET Examination students can try following  the steps given below - 

  • First understand the syllabus and Exam pattern of the NEET Exam

  • Try to cover each and every topic being mentioned in the syllabus, remember to stick to single-source whichever you choose

  • Start solving past year NEET MCQs to get an idea about the Exam (you can find all the past year solved MCQs on the website of Vedantu)

  • Learn the new concepts from the solutions of past year paper and evaluate your level of preparation

  • Make short notes of the new topics as per your understanding 

  • Keep solving more MCQs and have a regular habit of revising your notes 


With the blessing of your parents and your dedication to work hard, following these steps will make you crack the NEET Exam with great confidence and clarity.

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FAQs (Frequently Asked Questions)

1. What are some of the Examples of Linkage?

  • If you are clear with the concept of Linkage it is very easy to think about some of the Examples of Linkage. Take a clue from the Example given below - 

  • A Linkage between the hair colors and the eye colour is blonde hairs with blue eyes, black hairs with black or brown eyes. 

Here the Linkage is genetic and is inherited in nature.

2. What are the different types of Linkages we need to learn for the NEET Exam?

There are primarily two types of Linkages that are important for the NEET Exam - 

  • Complete Linkage - these are Linkages where the combination of characters appears together in more than two generations in a regular fashion, and due to the complete Linkage, only two types of gametes can be formed. 

  • Incomplete Linkage: these are Linkages where new gene combinations are formed in the progeny or offspring. It occurs due to the formation of a chiasma or Crossing Over between the linked genes.

3. How important is the topic Linkage and Crossing Over for the NEET Exam?

If a student analyzes the past year papers of NEET Exam they will find questions from the given topic. There can be a direct topic from the topic, also there is a good scope of indirect questions which could be solved only when the students have an idea about this particular topic. Therefore, we advise students to understand the topic explained well by the experts at Vedantu and solve the questions related to the topic to check the understanding.

4. What will happen if genes are fully or completely linked?

In a situation where the genes are fully or completely linked, then the probability of recombination is 0 (Zero). For more detail about the topic refer to the notes related to the topic or watch the video related to the topic.

5. What type of questions can we expect in the NEET Exam?

The NEET Exams has in total 180 questions and all the questions are in the form of MCQs. To get the questions right students need to have a strong conceptual clarity. There is also a pattern of negative marking so students need to practice the questions regularly and keep evaluating their level of preparation.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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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