Mutation Chromosomal Abberation

Mutation
Chromosomal Abberation
Change in chromosome
Chromosomal Arrangements
Diseases
Causes
Effects

1. “MUTATION”

2. Definition Cause of mutations (mutagen) Mutation frequency Types of mutations Chromosome mutations Point mutations Gene mutations Somatic mutations Kinds of gene mutation CONTENTS

3. “A mutation is a change in amount or structure of DNA of an organism.” A mutation may result in the change in appearance of a characteristic in a population. Definition:

4. There are certain physical and chemical agents which cause an Inheritable changes in a gene and thus produce its allele. These are Called Mutagens. These are three main categories of mutagens. Cause of Mutation (Mutagens)

5. These are high energy radiations like Alpha, beta, gamma and cosmic rays. They are called ionizing b/c they penetrate the tissues deeply causing ionization of molecules encountered. Ionizing Radiation:

6. As they penetrate the cells, electrons are forced to flow out of molecules, thus stable molecules and atoms are transferred into free radicals and reactive ions. These radiation affect the genetic material altering the purines and pyrimidines in the DNA and resulting in point mutation.

7. These include UV rays. These cannot ionize the target tissue. The UV light effect pyrimidines mainly to cause a change in DNA. Non Ionizing Radiation:

8. Certain chemicals such as nitrous acid hydroxylamine, dimethyl Sulfonate etc act as mutagens. In addition a variety of other Chemical substances including Mustard gas, caffeine, formaldehyde, certain components of tobacco & an increasing no. of drugs, food preservatives and pesticides also cause mutation. Chemical Mutagens:

9. Mutation occurs randomly and spontaneously, therefore any gene can undergoes mutation at any time. The rates at which occur also vary from species to species. The factors that alter mutation frequency include temperature, aging and malnutrition. MUTATION FREQUENCY:

10. The work of H.J Miller (1920) showed that frequency can be increased by X –rays. Since it has been shown the rate of mutation can by increased by the effect of different mutagens.

11. CHROMOSOME MUTATION

12. These changes may involve the loss or gain of single chromosomes, a condition called aneuploidy (2n-1 or 2n+1), or the increase in whole sets of chromosomes, a condition called euploidy (Polyploidy –3n, 4n, 5n & so on). CHANGE IN NO. Of CHROMOSOMES:

13. Zygotes containing less than the diploid no. of chromosomes (aneuploidy) usually fail to develop, but those with polysomic chromosomes may develop. In most cases where aneuploidy occurs in animals, it produces severe abnormalities. Chromosomal mutation in human are:

14. Down's Syndrome:

15. Patau Syndrome:

16. Edward Syndrome:

17. Turner Syndrome:

18. Metafemale Syndrome:

19. Klinefilter Syndrome:

20. Jacobsen Syndrome:

21. Structural change in chromosomes results from: Deletion and Duplication. Inversion and Translocation. Change in Structure of chromosome :

22. During these changes the no. of gene loci on chromosomes is changed and this has profound effect on phenotypes. Deletion and Duplication:

23. These changes result in change in allele sequence of parental linkage group and produced recombinant.But no change loci are lost.These produced profound effect of phenotype. b) Inversion and Translocation:

24. Point Mutation

25. “A change in nucleotides sequence of DNA molecule in a particular region of the chromosome is called a point mutation”. Such a change in the base sequence of a gene is transmitted to mRNA during transcription Point Mutation:

26. and may result in a change in the amino acid sequence of polypeptide chain produced from it during translation in ribosome .Since point mutations are changes in DNA, some occurs in any type of cell, somatic (somatic mutation)as well as germ cells (gene mutation).

27. Somatic mutation tends to remains undetected because dominant allele is present at that locus of homologous chromosome. They affect the organism in which these occur and lost on the death of an organism. In case of human mutation may produce cells with increased rate of growth and division. Somatic Mutation:

28. Gene Mutation

29. Gene mutations occurring during gamete formation are transmitted to all the cells of the offspring and from one generation to next therefore may be significant for the future of the species. Ge ne Mutation:

30. Most minor gene mutations are recessive; therefore pass unnoticed in the phenotype. However, there are cases where a change in single base have a profound effect on the phenotype, for example “sickle cell anemia” in humans, where mutation affect only single base in one of genes involved in the production of hemoglobin.

31. Kinds of Gene Mutation

32. “The mutation which arises for no apparent reason and cause a genetic alteration is called spontaneous mutation.” Spontaneous mutation is a random and natural. It may occur at any site of chromosome. It is found that majority of them produces just a slight effect and is harmful. Spontaneous Mutation :

33. The frequency of spontaneous mutations is 1-10/million gametes, but it should not be underestimated, as any higher organism contains thousands of gene loci.

34. Total mutation rate in Drosophila indicate in one generation there is probability that 5% of the gamete will contain a mutation which arose in that generation time. Drosophila :

35. Overall mutation frequency per generation in Humans is calculated to be 5% also. Humans:

36. “A mutation that is produced artificially during experimentation by using mutagens such as X-rays, UV rays, etc. is called induced mutation.” b) Induced Mutation :

37. c) Lethal & Detrimental Mutation

38. “Whose effect is drastic enough to eliminate the individual before reproductive age” Lethal Mutation :

39. “It may not kill the individual possessing it, but the gene is adversely affected him in some way and is decreasing his probability of survival”. Deterimental Mutation :

40. Once a gene has mutated to an allelic form, this mutant gene will continue to duplicate itself until it is eliminated together. However, at times the mutant gene may mutate back to the original or wild form of the gene. d ) Back Mutation :

41. This is called back mutation or reverse mutation. The frequency of back mutation is rare than the forward mutation, the change from wild to mutant.