Mutations-and-Change-

Mutations and Change in Chromosome Number and Structure

Overview

The changes in the genetic makeup of cells are called mutations.

  • The mutation alters the structure of chromosomes. Sometimes, a mutation occurs in the gamete and is then transmitted to offspring and future generations.
  • Sometimes these mutations hurt the phenotype. In this case, a mutant condition is taken as a genetic disorder or hereditary disease.
  • The creation of mutations is called mutagenesis.
  • Hermann and Muller in the 1920s, in some experiments, discovered the effect of X-rays on the genetic makeup of drosophila.
  • They observed genetic changes and then this mutant was used in his genetic studies.
  • Mutagenesis can occur in a number of ways. Errors during DNA replication, repair, or recombination can lead to insertions, deletions, or other mutations.
  • In this article, you will get to know about some important mutations.
Mutations and Change in Chromosome Number and Structure

Mutations can broadly be classified as (i) chromosomal aberration and (ii) point mutations. Chromosomal aberrations are mega changes that include the presence of an additional chromosome or loss of a chromosome from the diploid number of chromosomes, or changes like deletions, insertions, inversions, etc. in the parts of the chromosome, such chromosomal aberrations cause syndromes like Down’s syndrome, Klinefelter’ssyndrome and so on. Physical and Chemical disruption and errors take place during meiosis.

They can damage chromosomes or modify their number in a cell. There can be the following chromosomal alterations:

Change in Chromosome Number

In this case, the number of chromosomes in an affected person can be increased or decreased. The following types of chromosomal abnormalities are produced due to changes in chromosomal numbers.

Change-in-Chromosome-

(a) Aneuploidy:

It involves the addition or removal of one or a few chromosomes to the normal diploid set of chromosomes. The aneuploids occur due to the failure of the separation of homologous chromosomes of the particular set during meiosis. It is known as non-disjunction. As a result, two types of gametes are produced; one type consists of more chromosomes than the regular number, and the other type of gamete includes fewer chromosomes.

Aneuploidy is of the following types:

  1. Monosomic (2n-1):

They develop by the loss of one chromosome from the diploid set i.e., 2n-l. They can form two kinds of gametes, (n) and (n-1).

  1. Trisomic (2n+1):

These arise by the addition of an extra chromosome to the regular diploid set with the genetic formula, 2n + 1. Such individuals are formed by the union of an (n + 1) gamete with a regular gamete (n).

  1. Tetrasomic

These emerge by the addition of an extra pair of chromosomes to the diploid set with a chromosomal formula 2n + 2. By this, a specific chromosome is represented in 4 doses instead of a normal two.

  1. Nullisomic

These develop by the loss of a specific pair of chromosomes i.e., 2n-2. They occur by the blend of 2 (n-1) kinds of gametes.

(b) Euploidy:

Typically, the organism has two sets of chromosomes i.e., they are diploid (2n). At times there is an addition or loss of complete one set (n) or more than one set of chromosomes is observed. It is called as euploidy.

Euploidy is of the following types:

Euploidy 

(i) Haploidy or Monoploidy:

Out of two sets of chromosomes of a typical organism when one set is lost, the resulting offspring have simply one set of chromosomes (n).

(ii) Polyploidy:

Organisms having more than 2 normal sets of chromosomes (2n) are called polyploids. Organisms with three sets of chromosomes (2n + n) = 3n are triploids; those with four sets of chromosomes (2n + 2n) = 4n are tetraploids and those with 5 sets (2n + 3n) = 5n and six sets (2n + 4n) = 6n are called pentaploids and hexapodids respectively.

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Polyploidy comes from numerous methods. It might arise due to abnormal mitosis. Often diploid spores and gametes are produced due to defective meiotic division in which there is no reduction of chromosome number. Such diploid gametes fuse to form tetraploid individuals. Participation of more than two nuclei in fertilization in endosperm tissue of seed plants leads to polyploidy.

Change in Chromosome Structure

Sometimes there can be damage to chromosomes. It can produce a range of arrangements. These arrangements affect the genes of that chromosome. There are the following kinds of chromosomal structural changes:

1. Deletion:

The loss of part of the chromosome is called a deletion. Fragments without centimeters are usually lost during cell division. Therefore, the chromosome will miss certain genes.

Deletion

2. Duplication:

In this case, the fragment joins to the homologous chromosome with a duplication of genes.

3. Inversion:

In this case, the fragment reattaches to the original chromosome but in reverse orientation.

4. Translocation:

In this case, the fragment may join a non-homologous chromosome. Such change in location is called translocation.

Translocation

Point mutations

Point mutations are mutational changes that affect the message itself, producing changes in the sequence of DNA nucleotides. If modifications include only one or a couple of base sets in the coding series, they are called point mutations. While some point mutations happen due to spontaneous pairing errors that occur during DNA replication, others arise from damage to the DNA triggered by mutagens, typically radiations or chemicals.

The latter class of mutations is of particular practical significance because modern industrial industries frequently release lots of chemical mutagens into the environment.

Sickle cell anemia and phenylketonuria are popular examples of point mutation. In sickle cell anemia, a point mutation leads to the modification of amino acid glutamic acid into valine at position 6 from the N terminal end in the hemoglobin P chain. This consequently alters the tertiary structure of the hemoglobin particle, decreasing its ability to carry oxygen.

Point-mutations

In phenylketonuria, phenylalanine is not degraded because of the defective enzyme phenylalanine hydroxylase. Phenylalanine as a result collects in the cells leading to mental retardation, as the brain fails to establish in infancy. This condition is because of the point mutation.

MCQs with Answers: Mutations and Change in Chromosome Number and Structure

  1. What are mutations?
    • A. Only chromosomal changes
    • B. Only point mutations
    • C. Both chromosomal changes and point mutations
    • D. None of the above

    Answer: C

  2. When do mutations occur in gametes?
    • A. Never
    • B. Always
    • C. Occasionally
    • D. Only during DNA replication

    Answer: C

  3. Who discovered the effect of X-rays on the genetic makeup of drosophila?
    • A. Watson and Crick
    • B. Hermann and Muller
    • C. Mendel and Darwin
    • D. Rosalind Franklin

    Answer: B

  4. What is the term for mega changes that include the presence of an additional chromosome or loss of a chromosome?
    • A. Point mutations
    • B. Chromosomal aberrations
    • C. Deletions
    • D. Insertions

    Answer: B

  5. Which of the following is NOT a chromosomal aberration?
    • A. Aneuploidy
    • B. Euploidy
    • C. Duplication
    • D. Point mutation

    Answer: D

  6. What is the condition where there is the addition or removal of one or few chromosomes to the normal diploid set of chromosomes?
    • A. Duplication
    • B. Aneuploidy
    • C. Euploidy
    • D. Inversion

    Answer: B

  7. What type of gametes are produced in Monosomic individuals?
    • A. (n)
    • B. (n-1)
    • C. (n+1)
    • D. (2n)

    Answer: B

  8. What is Polyploidy?
    • A. Loss of a pair of chromosomes
    • B. Addition or loss of complete one set of chromosomes
    • C. Having more than 2 normal sets of chromosomes
    • D. Loss of part of the chromosome

    Answer: C

  9. What is the structural change where the fragment reattaches to the original chromosome but in reverse orientation?
    • A. Deletion
    • B. Duplication
    • C. Inversion
    • D. Translocation

    Answer: C

  10. Which type of mutation affects the sequence of DNA nucleotide?
    • A. Aneuploidy
    • B. Polyploidy
    • C. Point mutations
    • D. Euploidy

    Answer: C

  11. What is the significance of sickle cell anemia in relation to mutations?
    • A. Point mutation causes a change in amino acid sequence
    • B. Deletion of a chromosome
    • C. Inversion of a gene
    • D. Polyploidy

    Answer: A

  12. In phenylketonuria, what causes the condition?
    • A. Duplication
    • B. Aneuploidy
    • C. Point mutation
    • D. Inversion

    Answer: C

  13. What triggers some point mutations?
    • A. Spontaneous pairing errors during DNA replication
    • B. Presence of chromosomes
    • C. Meiosis
    • D. Aneuploidy

    Answer: A

  14. What is the condition where organisms have three sets of chromosomes?
    • A. Triploids
    • B. Tetraploids
    • C. Pentaploids
    • D. Hexaploids

    Answer: A

  15. What is the term for the creation of mutations?
    • A. Mutagenesis
    • B. Mutationation
    • C. Mutatogenesis
    • D. Mutatosynthesis

    Answer: A

  16. Who observed genetic changes in drosophila due to X-rays in the 1920s?
    • A. Watson and Crick
    • B. Rosalind Franklin
    • C. Hermann and Muller
    • D. Mendel and Darwin

    Answer: C

  17. What are chromosomal aberrations?
    • A. Only point mutations
    • B. Only polyploidy
    • C. Mega changes involving chromosomes
    • D. Duplication of chromosomes

    Answer: C

  18. What is the term for the loss of part of the chromosome?
    • A. Insertion
    • B. Deletion
    • C. Duplication
    • D. Inversion

    Answer: B

  19. What is the genetic formula for Trisomic individuals?
    • A. 2n-1
    • B. 2n+1
    • C. 2n+2
    • D. 2n-2

    Answer: B

  20. How do point mutations caused by mutagens differ from those during DNA replication?
    • A. They have the same origin
    • B. Mutagens cause errors in DNA repair
    • C. Mutagens are caused by radiations or chemicals
    • D. Both A and B

    Answer: C

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FAQs: Mutations and Changes in Chromosome Number and Structure

  1. What are mutations?
    • Mutations are changes in the genetic makeup of cells that alter the structure of chromosomes.
  2. How can mutations affect offspring?
    • Mutations can be transmitted to offspring through gametes, sometimes leading to genetic disorders or hereditary diseases.
  3. Who discovered the effect of X-rays on the genetic makeup of drosophila?
    • Hermann and Muller, in the 1920s, discovered the effect of X-rays on the genetic makeup of drosophila.
  4. What is mutagenesis?
    • Mutagenesis is the creation of mutations, which can occur in various ways such as errors during DNA replication, repair, or recombination.
  5. How are mutations classified?
    • Mutations are broadly classified as chromosomal aberrations and point mutations.
  6. What are chromosomal aberrations?
    • Chromosomal aberrations are mega changes involving chromosomes, including the presence of an additional chromosome or loss of a chromosome, leading to syndromes like Down’s syndrome and Klinefelter’s syndrome.
  7. How can the number of chromosomes change?
    • The number of chromosomes can change through aneuploidy (addition or removal of one or few chromosomes) and euploidy (addition or loss of complete sets of chromosomes).
  8. What is aneuploidy?
    • Aneuploidy involves the addition or removal of one or few chromosomes from the normal diploid set, leading to conditions like monosomy and trisomy.
  9. What is euploidy?
    • Euploidy involves the addition or loss of complete sets of chromosomes, including haploidy (one set) and polyploidy (more than two sets).
  10. How does polyploidy occur?
    • Polyploidy may arise due to abnormal mitosis, defective meiotic division, or the participation of more than two nuclei in fertilization.
  11. What are chromosomal structural changes?
    • Chromosomal structural changes include deletion (loss of part of the chromosome), duplication (duplication of genes), inversion (fragment reattaches in reverse orientation), and translocation (fragment joins a non-homologous chromosome).
  12. What are point mutations?
    • Point mutations are changes in the sequence of DNA nucleotides affecting the message itself. They can be caused by spontaneous pairing errors during DNA replication or by mutagens such as radiations or chemicals.
  13. Can you provide examples of point mutations?
    • Sickle cell anemia and phenylketonuria are examples of point mutations.
  14. How does sickle cell anemia result from a point mutation?
    • In sickle cell anemia, a point mutation leads to the substitution of amino acid glutamic acid into valine, altering the tertiary structure of hemoglobin.
  15. What is the significance of phenylketonuria in relation to point mutations?
    • Phenylketonuria results from a point mutation, leading to the defective enzyme phenylalanine hydroxylase, causing the accumulation of phenylalanine in cells and leading to mental retardation.
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Wrap up

The tutorial provides a comprehensive overview of mutations and alterations in chromosome number and structure. It emphasizes the significance of mutations, which are changes in the genetic makeup of cells, often leading to alterations in chromosome structure. The impact of mutations on offspring and future generations, either causing genetic disorders or hereditary diseases, is explored.

The tutorial delves into the two broad classifications of mutations: chromosomal aberrations and point mutations. Chromosomal aberrations involve significant changes, including the presence of additional or loss of chromosomes, leading to conditions like Down’s syndrome and Klinefelter’s syndrome. The detailed exploration of aneuploidy and euploidy sheds light on abnormalities in chromosomal numbers.

Aneuploidy, characterized by the addition or removal of chromosomes, is further explained through types such as monosomic, trisomic, tetrasomic, and nullisomic. Euploidy, involving the addition or loss of complete sets of chromosomes, includes haploidy (monoploidy) and polyploidy. Various types of polyploidy, such as triploids and tetraploids, are discussed.

The tutorial also addresses changes in chromosome structure, encompassing deletion, duplication, inversion, and translocation. Each structural change is elucidated, providing a comprehensive understanding of how these alterations can impact genes within the chromosome.

The section on point mutations focuses on mutational changes affecting the DNA nucleotide sequence. Examples such as sickle cell anemia and phenylketonuria highlight the practical significance of point mutations and their implications for human health.

In summary, the tutorial offers a detailed exploration of mutations, chromosomal aberrations, alterations in chromosome number and structure, and point mutations. It serves as a valuable resource for understanding the complexities of genetic changes and their diverse consequences.