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    Chromosomal Theory of Inheritance – An Overview and Basis of Inheritance

    Chromosomal Theory of Inheritance was proposed by two scientist Theodor Boveri and Walter Sutton. According to this Theory, chromosomes are the carriers of genetic material.

    BiologyBiology ArticleChromosomal Theory Of Inheritance

    Chromosomal Theory of Inheritance

    Chromosomal Theory of Inheritance What are Chromosomes?

    Chromosomes are a thread-like structure of nucleic acids and protein located within the nucleus of the living cells and are mainly involved in carrying genetic information in the form of genes.

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    The Chromosomal Theory of Inheritance

    The chromosomal theory of inheritance was given by Boveri and Sutton in the early 1900s. It is the fundamental theory of genetics. According to this theory, genes are the units of heredity and are found in the chromosomes.

    Chromosomal Theory of Inheritance came into existence long after Mendelian genetics. During Mendel’s experimentation, the society was not acceptable to such drastic changes in their scientific ideas. They could not believe the existence of such discrete factors such as genes which would segregate without mixing as this did not support their idea of the constant changes leading to evolution. Moreover, the means of communication was poor at that time as a result of which, the information could not be conveyed to the masses. Also, Mendel’s mathematical approach to prove biological laws was unacceptable.

    As time passed, scientists Vries, Correns and Tschermak discovered chromosomes which existed inside the nucleus. Sutton and Boveri discovered observed the behaviour of the chromosomes when the cells were divided. With the advancements in the microscope, this task became easier. Hence, they proved Mendel’s laws with the help of chromosomal movement. They showed the segregation of the chromosomes during the Anaphase of cell division. The idea of chromosomal segregation combined with the Mendelian principles gave rise to the chromosomal theory of Inheritance. The work was further carried forward and proved by T.H. Morgan, who used Drosophila melanogaster to show how sexual reproduction gave rise to variations.

    Chromosomal theory: Linkage and Genetic Recombination

    Morgan observed that while crossing a set of characteristics, two genes did not segregate as per Mendel’s law. If two genes were present on the same chromosome, the probability of getting a parental combination was much higher in the next generation compared to the non-parental combination. This physical association of genes was termed as linkage. The term genetic recombination described the non-parental gene combinations in a dihybrid cross. Once, linked genes were discovered, the frequency of linked genes also influenced the appearance of traits in the next generation. A student of Morgan, Sturtevant discovered the position of linked genes on a chromosome by calculating their frequency of genetic recombination by the process of gene mapping. This method of generating a link map was extensively used during the Human Genome Project.

    Also, read  Human Genome Project

    Observations of Chromosomal Theory of Inheritance

    The Chromosomal Theory of Inheritance supports Mendel’s laws. Listed below are the observations of this theory:

    During the process of cell division-meiosis, the pairs of homologous chromosome move as discrete structures, which are independent of other pairs of chromosomes.

    There is a random distribution of chromosomes into the pre-gametes from each homologous pair.

    Each parent synthesizes gametes, which constitute only half of their chromosomal complement.

    Even though female (egg) and male (sperm) gametes differ in their size and morphology, they have the same number of chromosomes, submitting equal genetic contributions from each parent.

    The gametic chromosomes fuse during fertilization to produce offspring with the same number of a chromosome as their parents.

    Some Important Questions on Chromosomal Theory of Inheritance

    Who discovered chromosomes?

    Carl Wilhelm von Nageli, a Swiss botanist discovered chromosomes and he was a first person to study about the cell divisions

    What is the chromosomal theory of inheritance?

    It is the fundamental theory of genetics which recognizes chromosomes as the carriers of genetic material.

    Who proposed the chromosomal theory of inheritance?

    Theodor Boveri and Walter Sutton are the two scientists who were credited with developing the Chromosomal Theory of Inheritance.

    What is Mutations?

    The mutation is defined as the change or the permanent alteration of the nucleotide sequence of the genome of an organism.

    Stay tuned with BYJU’S to know more in detail about the chromosomal theory of inheritance.

    Quiz of the Day!

    Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

    Select the correct answer and click on the “Finish” button

    Check your score and answers at the end of the quiz

    स्रोत : byjus.com

    Chromosomal Theory of Inheritance

    Learn about Chromosomal Theory of Inheritance topic of Biology in details explained by subject experts on Vedantu.com. Register free for online tutoring session to clear your doubts.

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    What are Chromosomes?

    Where do genes find themselves in a cell? Odds are, you have heard the punchline before: genes lie on chromosomes. You may have even heard the second punchline, the one that is ushered in the modern genetic age: genes are DNA stretches specifying proteins.

    Chromosomes are a thread-like structure of nucleic acids and proteins located within the nucleus of living cells and are primarily involved in gene-shaped genetic information. The Swiss botanist Carl Wilhelm von Nageli discovered chromosomes and was the first person to research the cell divisions.

    The Chromosomal Theory of Inheritance

    It is the fundamental genetic theory that recognizes chromosomes as the bearers of genetic material. Theodor Boveri and Walter Sutton are the two scientists who have been credited with developing the Inheritance Chromosomal Theory. In the early 1900s, Boveri and Sutton gave the chromosomal theory of inheritance. It is the fundamental genetic theory. According to this theory, genes are heredity units, and they are found in the chromosomes. Inheritance chromosomal theory came into being long after Mendelian genetics. Society wasn't acceptable to such drastic changes in their scientific ideas during Mendel's experimentation. They did not believe there were such distinct variables as genes that would Separate without combining, as this did not help their notion of continuous evolutionary shifts.

    In addition, the means of communication at that time were weak, as a result of which the information could not be transmitted to the masses. Mendel's scientific approach to proving biological rules has always been inappropriate. Scientists Vries, Correns, and Tschermak found chromosomes that remained within the nucleus as time passed. Sutton and Boveri discovered when the cells were divided they observed the behaviour of the chromosomes. This task became simpler with the advances in the microscope. Thus, they proved the laws of Mendel with the aid of chromosomal motion. They showed chromosome segregation during the cell division Anaphase. The idea of chromosomal segregation combined with the Mendelian principles has given rise to Inheritance's Chromosomal Theory. The research was carried out further and was proved by T.H. Morgan, who used Drosophila melanogaster to demonstrate how it induced differences in sexual reproduction.

    Chromosomal Theory - Linkage and Genetic Recombination

    Morgan found that two genes did not segregate as per Mendel's law when crossing a range of characteristics. If two genes were present on the same chromosome, the probability of obtaining a parental combination in the next generation was much higher compared with the non-parental combination. This physical gene association was termed a connection. In a dihybrid cross, the word genetic recombination identifies the combinations of non-parental genes. Once connected genes were discovered, the frequency of connected genes also influenced trait appearance in the next generation. A Morgan’s student, Sturtevant, discovered the location of the related genes on a chromosome by measuring their genetic recombination frequency using the gene mapping technique. This method of producing a map of ties was commonly used during the Human Genome Project.

    Observations of Chromosomal Theory of Inheritance

    The inheritance chromosomal theory supports Mendel's laws. The observations of this theory are listed below:

    The pairs of homologous chromosomes migrate as discrete structures independent of other chromosome pairs during the process of cell division-meiosis.;

    Chromosomes of each homologous pair are randomly distributed into pre-gametes.

    Gametes are synthesized by each parent and contain just half of their chromosomal complement.

    While the size and shape of the male and female gametes (sperm and egg) vary, they have the same number of chromosomes, indicating similar genetic contributions for each parent.

    During fertilization, gametic chromosomes combine to produce offspring with the same number of chromosomes as their parents.

    Key Points

    Boveri and Sutton's inheritance chromosome theory states that genes are found at specific chromosome locations, and that chromosome behaviour during meiosis may explain Mendel's inheritance laws. Thomas Hunt Morgan, who studied fruit flies, provided the first strong confirmation of the chromosome theory.

    Morgan discovered a mutation affecting the colour of the fly-eye. He noted male and female flies inherited the mutation differently.

    Following the pattern of inheritance, Morgan assumed that the eye colour gene must be located on the X chromosome.

    What is Mutation?

    The mutation is defined as the change or the permanent alteration of the nucleotide sequence of the genome of an organism. Our DNA can undergo changes in its basic sequences A, C, G and T. This results in changes in proteins that are DNA-synthesized. Generally, the cells can identify and restore any damage that could be done by mutation until it is permanent.

    The Causes of Mutation 

    The mutation results in genetic differences between the species. Few mutations with positive effects are transferred to successive generations. For example, sickle cell anaemia is the result of a mutation in the gene that codes for the synthesis of the protein haemoglobin. The red blood cells take the form of a sickle. Within the African population, however, this mutation also protects against malaria.

    स्रोत : www.vedantu.com

    The chromosomal basis of inheritance (article)

    Thomas Hunt Morgan's experiments. The fruit fly (Drosophila melanogaster) as a model system.

    Chromosomal inheritance

    The chromosomal basis of inheritance

    Thomas Hunt Morgan's experiments. The fruit fly (Drosophila melanogaster) as a model system.

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    Key points:

    Boveri and Sutton's chromosome theory of inheritance states that genes are found at specific locations on chromosomes, and that the behavior of chromosomes during meiosis can explain Mendel’s laws of inheritance.

    Thomas Hunt Morgan, who studied fruit flies, provided the first strong confirmation of the chromosome theory.

    Morgan discovered a mutation that affected fly eye color. He observed that the mutation was inherited differently by male and female flies.

    Based on the inheritance pattern, Morgan concluded that the eye color gene must be located on the X chromosome.

    Introduction

    Where are genes found in a cell? Odds are, you've already heard the punchline: genes lie on chromosomes. You may have even have heard the second punchline, the one that ushered in the modern genetic era: genes are stretches of DNA that specify proteins.

    However, these were not always things that you could look up on Khan Academy! When Gregor Mendel began studying heredity in 1843, chromosomes had not yet been observed under a microscope. Only with better microscopes and techniques during the late 1800s could cell biologists begin to stain and observe subcellular structures, seeing what they did during cell divisions (mitosis and meiosis).

    Eventually, some scientists began to study Mendel’s long-ignored work and re-evaluate his model in terms of the behavior of chromosomes. Around the turn of the 20th century, the biology community started to make the first tentative connections between chromosomes, meiosis, and the inheritance of genes

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    The chromosome theory of inheritance

    Who figured out that genes are on chromosomes? Walter Sutton and Theodor Boveri generally get credit for this insight. Sutton, who was American, studied chromosomes and meiosis in grasshoppers. Boveri, who was German, studied the same things in sea urchins.

    In 1902 and 1903, Sutton and Boveri published independent papers proposing what we now call the chromosome theory of inheritance. This theory states that individual genes are found at specific locations on particular chromosomes, and that the behavior of chromosomes during meiosis can explain why genes are inherited according to Mendel’s laws

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    Photographs of Walter Sutton, Theodor Boveri, and Thomas Hunt Morgan.

    _Modified from "Chromosomal theory of inheritance: Figure 1," by OpenStax College, Biology (CC BY 3.0) and from "Thomas Hunt Morgan," (public domain)._

    Observations that support the chromosome theory of inheritance include

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    Chromosomes, like Mendel's genes, come in matched (homologous) pairs in an organism. For both genes and chromosomes, one member of the pair comes from the mother and one from the father. [See diagram]

    The members of a homologous pair separate in meiosis, so each sperm or egg receives just one member. This process mirrors segregation of alleles into gametes in Mendel's law of segregation. [See diagram]

    The members of different chromosome pairs are sorted into gametes independently of one another in meiosis, just like the alleles of different genes in Mendel's law of independent assortment. [See diagram]

    The chromosome theory of inheritance was proposed before there was any direct evidence that traits were carried on chromosomes, and it was controversial at first. In the end, it was confirmed through the work of geneticist Thomas Hunt Morgan and his students, who studied the genetics of fruit flies

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    T. H. Morgan: Fun with fruit flies

    Morgan chose the fruit fly, Drosophila melanogaster, for his genetic studies. What fruit flies may lack in charisma (depending on your taste in insects), they make up for in practicality: they're cheap, easy, and fast to grow. You can raise hundreds of them in a little bottle with sugar sludge at the bottom, and many geneticists still do this today!

    Image of a fruit fly, photographed from the top.

    Image credit: "Drosophila melanogaster - top," by André Karwath (CC BY-SA 2.5).

    Morgan's crucial, chromosome theory-verifying experiments began when he found a mutation in a gene affecting fly eye color. This mutation made a fly's eyes white, rather than their normal red.

    Unexpectedly, Morgan found that the eye color gene was inherited in different patterns by male and female flies

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    . Male flies have an X and a Y chromosome (XY), while female flies have two X chromosomes (XX). It didn't take Morgan long to realize that the eye color gene was being inherited in the same pattern as the X chromosome.

    स्रोत : www.khanacademy.org

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