Mutation AND Polyploidy

Mutation Cause - mutation
Gene - DNA - Sequence of nucleotide

• The term mutation was coined by Hugo De Vries and is defined as "Sudden change in DNA or chromosome which is heritable".
• The factors which cause mutation are called mutagen. It may be physical or chemical mutagen. Any physical factor like prolonged exposure to sunlight UV ray, IR rays etc are called physical muta (mutagen). The high energy of them changes sequence of nucleotides in DNA or chromosome size or number.
• Any chemical factor that changes sequence of nucleotide in DNA or chromosomes is called chemical mutagen.

Types of Mutation

• Based on the cell involved mutation is of two types: Somatic mutation and Germinal mutation.

-> When mutation occurs in somatic cells it is called somatic mutation which cannot be transmitted. When protooncogene is changed and become oncogene it causes cancer.

-> When mutation occurs in reproductive cells like sperms and ova it is called germinal mutation which is heritable.

• Based on origin mutation is of two types:
  Gene mutation : chromosomal mutation.

1) Gene mutation

• A segment of DNA that determines characters is called Gene which occupies specific position in chromosome this position is called locus. The segment of DNA is a sequence of deoxyribonucleotide.
• When a deoxyribonucleotide is added or lost it changes whole sequence of deoxyribonucleotides. Sometimes a deoxyribonucleotide is replaced with another deoxyribonucleotide. Based on it gene mutation has two sub-types:

a) Frame shift mutation:

• When deoxyribonucleotide is added or lost from the segment of DNA it is called frame shift mutation. When addition or deletion occurs at the beginning it bring more change.
  It can be represented as,
  THE CAT HAD HAT
  ↓ On missing H of first segment from the it becomes
  TEC ATH ADH ...

b) Substitution mutation:

• When deoxyribonucleotide of a kind replaced with deoxyribonucleotide of some kind or different kind is called substitution mutation. It is called of sub-type

i) Transversion, transition

1. The substitution mutation in which purine is replaced with purine and pyrimidine is replaced with pyrimidine. It is called transition.
2. Some time purine is replaced with pyrimidine & vice-versa, this kind of substitution is called transversion.

2) Chromosomal mutation

The mutation caused by alteration of chromosome size and chromosome number is called chromosomal mutation. It is of two types structural & numerical chromosomal mutation.

a) Structural chromosomal mutation:

When mistakes are made during gamete formation the size of chromosome might be changed if so then genes are either blocks or added this kind of mutation is called structural chromosomal mutation. Following events are essential for this purpose.

Deletion:
When certain segment chromosome is lost during exchange of non-sister chromatids it is called deletion. In this case certain body traits are not appeared and is mostly lethal.

Inversion:
When the segment of chromosome is rejoin at opposite orientation it is called inversion.

Translocation (Non-homologous chromosome)
-> When segment of chromosome are exchanged between non-homologous chromosome it is called translocation. It is lethal.

Duplication:
-> When a segment of chromosome is added to the homologous chromosome then certain genes are repeated this phenomenon is called Duplication.

b) Numerical chromosomal mutation

It is also called chromosomal aberration in which number of chromosome is altered in zygote.

Each sexually reproducing organism has two sets of chromosome one from father and another from mother. In case of human maternal set has 23 chromosome and Paternal 23 chromosome. Each set of chromosome is called ploid. And zygote has two. This condition is called diploid. The gamete has single ploid and is called haploid.

The exact multiple of ploid is called euploid like diploid for (2n), triploid for (3n) tetraploid for (4n) and so on.

When number of chromosome is changed in Ploidy or the number of ploid is changed it is called Numerical chromosomal mutation.

1) Aneuploidy:

-> When one or one pair of chromosome is added or deleted from zygote it is called Aneuploidy. It is further classified as hypoploidy and hyperploidy.

a. Hypoploidy:

When one or one pair of chromosome is deleted from zygote it is called hypoploidy. When one chromosome is lossed from zygote it is called monosomy (2n-1) in this case certain chromosome does not have pair and is single in the cell. Turner syndrome is monosomy for sex chromosome (XO).

When one pair of chromosome is lossed from zygote it is called nullisomy (2n-2) pair. In this case certain chromosome is lossed from zygote.

b. Hyperploidy:

When one or one pair of chromosome is added to zygote it is called Hyperploidy. In this case numbers of chromosome are increased. It is classified as trisomy and tetrasomy. When one chromosome is added to zygote it is called tri-somy. In this case certain chromosome is available in three number. When chromosome number 21 has three chromosome it is called trisomy 21 that causes Down syndrome. Similarly tri-somy 18 causes Edward syndrome. Tri-somy 13 causes Patau's syndrome and trisomy of sex chromosome causes Klinefelter's syndrome (XXY).

When one pair of chromosome is added to zygote it is called tetrasomy. In this case certain chromosome is available in 4 number.

2. Polyploidy:

-> Ploidy is set of chromosome.
-> When chromosome numbers are multiplies.

Autopolyploidy

-> The process of multiplying number of ploidy in zygote it is called polyploidy. This method is widely used in plants to develop new variety or species.

• It is of two types:
  • Autopolyploidy
  • Allopolyploidy

a) Autopolyploidy:

When different varieties of a species are used to increased numbers of ploid it is called Autopolyploid. It is widely to used in developing new variety of a species. Autopolyploidy might be trip-ploidy and tetraploidy etc. But trip-ploidy is seed less.

b) Allopolyploidy:

When members of different species are crops in order to multiply numbers of ploid it is called Allopolyploidy. It is widely used in plants to develop new species.

Example: 1
Development of Raphanobrassica
-> George Karperchenko performed experiments on radish and cabbage which belongs to the same family brassica. they have (2n) equals (18) and are Allide species. Karperchenko has following crosses.

After many crosses he obtain fertile plant and is called Raphanobrassica which is tetra-ploid. It is non-economical as it had root of Cabbage and leaves of raddish.

Example: 2
Development of modern day wheat (Triticum aestivum)
Triticum aestivum is a hexaploid and is an example of yellow polyploid the development of modern day wheat can be represented as:

Significance of Polyploidy

1. It is an important Source of Variation and helps in evolution of species and Varieties.
2. Disease resistance and high yielding Varieties can be prepared through allopolyploidy.
3. Polyploidy results in the change in season of flowering and fruiting.
4. Seedless varieties of watermelon, tomato, grape others alike can be prepared through autopolyploidy.