Botany lecture notes

Mutation Breeding Technique for the Improvement of Crop Plants (with PPT)


what is mutation breeding

Mutation Breeding
(Induced Mutations for Crop Improvement)

What is mutation?

Mutation is the “Sudden heritable change in an organism”. Mutation may be the change in gene, chromosome or plasmagene (genetic material inside mitochondria and chloroplasts. The mutation produced by change in the base sequence of gene is called point mutation or gene mutation. The gene mutation may be further classified as transition, transversion, deletion, duplication or inversion. Chromosomal mutations are the change in chromosome structure. The change in the structure of chromosome can occur as a result of large deletion, inversion, duplication, translocation and change in chromosome number. Most of the mutations are lethal to the organism. A very small number of mutations are beneficial to the organism. Additionally, by the use of mutation inducing agents, a breeder can induce desirable changes in the genetic constitution of plants and thereby he can improve the performance of a cultivated variety.

Mutation Breeding

Definition: “The utilization of induced mutations in crop improvement is called mutation breeding”

The term mutation breeding was first coined by Freisleben and Lein in 1944 to refer to the deliberate induction and development of mutant lines for crop improvement.

Spontaneous and Induced mutations:

(1). Spontaneous mutation:

Mutation occurs in nature are called spontaneous mutation. Spontaneous mutation occurs in the organism without any treatment at low rate in the nature. The frequency of spontaneous mutation is 10-6 (one in 10 lakhs). Different genes in and organism show different mutation rate.

(2). Induced mutation:

Mutations induced in an organism by treatment with physical or chemical mutagen are called induced mutations. The agents which are used to induce mutation are called mutagens. Certain genes in an organism promote the mutation of other genes nearby in the chromosomes. For example, the gene Dt in Chromosome number 9 of maize increases mutation rate of other genes.

Characteristics of Mutation:

Ø  Mutations are generally recessive; Dominant mutations do occur in nature.

Ø  Mutations are generally harmful to organism; small percentage of mutation is beneficial.

Ø  Mutation occurs at random in the chromosome, may occur in any gene.

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Botany lecture notes

Host Selective and Non-Host Selective Toxins in Host Parasite Interactions and Pathogenesis


toxins in plant pathogen interactions

Toxins in Plant Pathogenesis
Toxins in Plant Pathogen Interaction

The process of pathogenesis (the onset of diseased condition) in plants is facilitated by many factors such as virulence of the pathogen, susceptibility of the host, presence of suitable environmental conditions and various enzymes and metabolites of pathogens. Previously we have discussed the importance of different enzymes involved in plant pathogen interactions. These enzymes facilitate the entry of the pathogen into the host and help to colonize inside the host cell. The production of different hydrolytic enzymes may not always result in the establishment of pathogen inside the host tissue. Certain plant pathogen may successfully invade the host tissue area but fail to induce the onset of disease. These findings highlighted the involvement of certain toxins, microbial toxins or aggressins, in the establishment of diseased conditions in plants. The present post describes the Toxins involved in plant pathogen interaction and pathogenesis with examples.

What is meant by ‘toxin’ in Plant Pathology?

Ø  Definition: Any substances produced by a pathogen which is injurious to host and it directly and immediately play a crucial role in pathogenesis.

Ø  Toxins involved in plant parasite interactions are also called as aggressin.

Ø  According to Koch’s postulates, a substance to be called as a ‘toxin’ should follow the following criterions:

@.   The compound must be isolated from the diseased plant

@.   It should NOT be present in the healthy plant

@.   Compound must be chemically characterized

@.   When isolated toxin is reintroduced to a healthy host, it should produce the original symptoms.

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Molecular Biology Tutorials

Folded Fibre Model of Chromosomes


Dupraw model of chromosome

Folded Fibre Model of Chromosome
(The Ultra-structural Organization of DNA and Histone Proteins in the Chromosomes)

The chromosomes of eukaryotic organisms are a complex structural organization of DNA and proteins. The exact structural organization of proteins and DNA to form the chromatin material (or chromosomes during cell division) is a curious question in the scientific community. This curiosity becomes a wonder when we realize the total length of DNA in a single cell and size of the nucleus in which this DNA is residing. For example, in a diploid human cell, there will be 46 chromosomes. The DNA in all these 46 chromosomes when joined together, it will have a distance of about 2.2 meters. Thus, the average length of DNA in a single chromosome will be 4.8 cm or 48,000 µm (2.2 X 100/46). On an average, the human chromosome at its metaphase stage is about 6 µm long. This means the 48,000 µm long DNA strand is heavily folded to from the 6 µm long chromosome with a packing ratio of about 8000 : 1. The exact folding pattern of DNA is a highly debated concept.  For explaining the structural organization of DNA and proteins in the chromosome, various theories have been put forward by different scientists. DuPraw Folded Fibre Model and Nucleosome Model are the two such models trying to explain the ultra-structural organization of DNA and proteins in the chromosome. The present post describes the significance of Folded Fibre Model of Chromosomes and its merits and demerits.

Folded Fibre Model of Chromosome

Ø  The Folded Fibre Model of chromosome was proposed by DuPraw in 1965.

Ø  He published this model based on his studies on human chromosomes using electron microscope.

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Molecular Biology Tutorials

Karyotype and Idiogram: Definition and Importance of Karyotype Test (Karyotyping) in Human


what is karyotyping

(image source: wikipedia)

Karyotype, Karyotyping and Preparation of Idiogram

What is a Karyotype?

All species are characterized by a set of chromosomes to carry their genetic information. The chromosomal composition of each species has a number of characteristics. The Karyotype is a set of characteristics that identifies and describes a particular set of chromosome. These characteristics which are described by a karyotype are:-

(1).  The chromosome number

(2).  Relative size of different chromosomes

(3).  Position of centromere and length of chromosomal arms

(4).  Presence of secondary constrictions and satellites

(5).  Banding pattern of the chromosome

(6).  Features of sex chromosomes

What is Karyotyping? How to Prepare the Karyotype of Human?

Ø  The process of preparation of the karyotype of a species is called Karyotyping.

Ø  Karyotyping is now most commonly used in clinical diagnosis and clinical genetics.

Ø  Karyotype is prepared from the microphotographs of metaphase chromosomes.

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Molecular Biology Tutorials

Classification of Chromosomes based on Position of Centromere and Length of Chromosomal Arms

how chromosomes are classified

Classification of Chromosomes Based on Position of Centromere and Length of Arms

Ø  The size and shape of the chromosomes are variable in the different phases of cell cycle.

Ø  Chromosomes in the interphase of cell appear as thin, coiled, elastic and thread-like structures.

Ø  This thread-like stainable interphase chromosome is called chromatin.

Ø  During the mitotic or meiotic cell division, the chromatin materials become thicker in their width and shorter in their length.

Ø  Chromosomes in the metaphase stage of cell division show maximum condensation.

Ø  Each metaphase chromosome contains a centromere (primary constriction).

Ø  The centromere divides the chromosome into two parts called chromosomal arms.

Ø  The small arm of the chromosome is denoted as ‘p’ – arm, whereas the large arm is denoted as the ‘q’ – arm.

Ø  When chromosomes are represented as a karyotype or ideogram, each chromosome is arranged in such a way that the ‘p’ arm is positioned above the centromere and the q arm is represented below the centromere.

Ø  The position of centromere and the relative size of chromosomal arms are used as a criterion for a morphological classification of chromosomes.

Ø  This morphological classification is an important karyotypic feature of an organism.

Classification of chromosome

Ø  Based on the position of centromere and length of chromosomal arms, the chromosomes are classified into 4 groups:

(1).      Telocentric chromosomes

(2).      Acrocentric chromosomes

(3).      Sub-metacentric chromosomes

(4).      Metacentric chromosomes

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