Plant materials brought into a country must be free from pathogens. It may lead to outbreak of new disease or introduction of a new pathogen into the environment. Thus plant materials (seeds / saplings) are tested in plant quarantine.

Genetically Modified Organisms:
(i) Genetic modification refers to the alteration or manipulation of genes in the organisms using rDNA techniques in order to produce the desired characteristics.
(ii) The DNA fragment inserted is called transgene. Plants or animals expressing a modified endogenous gene or a foreign gene are also known as transgenic organisms.
Advantages:
(i) The transgenic plants are much stable, with improved nutritional quality, resistant to diseases and tolerant to various environment conditions.
(ii) Similarly transgenic animals are used to produce proteins of medicinal importance at low cost and improve livestock quality. eg Golden Rice is a genetically modified Rice which can produce Beta carotene.

(i) The human genome has 3 billion base pairs. Each person's DNA sequence is unique due to the small difference in the base pairs.
(ii) DNA finger printing is the easier & quicker method to compare the genetic difference among the two individuals. This technique was developed by Alec Jeffrey.
(iii) The technique analyses each individual's unique DNA sequences and provides distinctive characteristics of individual which helps in identification.
(iv) Variable Number of Tandem Repeat sequences (VNTRs) serve as molecular markers for identification.
(v) In human beings, 99% of the DNA base sequences are the same and this is called as bulk genomic DNA.
(vi) The remaining 1% DNA sequence differs from one individual to another. and is present as small stretch of repeated sequences which is known as satellite DNA.
(vii) The number of copies of the repeat sequence also called as VNTRs differs from one individual to another, and results in variation in the size of the DNA segment.
(viii) Satellite DNA bring about variation within the population. Variation in DNA banding pattern reveals differences among the individuals.
Applications of DNA Fingerprinting:
(ix) DNA fingerprinting technique is widely used in forensic applications like crime investigation such as identifying the culprit. It is also used for paternity testing in case of disputes.
(x) It also helps in the study of genetic diversity

(i) Sexually reproducing organisms have two complete set of chromosomes in their somatic cells. This is called diploid (2n).
(ii) The gametic cells have only one set of chromosome. This is called haploid (n).
(iii)  An organism having more than two sets of chromosomes is called polyploid. Such condition is called Polyploidy.
(iv) It can be induced by physical agents such as heat or cold treatments, X-rays, Chemical agents like colchicine.
Achievements of polyploidy breeding:
(i) Seedless watermelons (3n) and bananas (3n).
(ii) TV-29 (triploid variety of tea) with larger shoots and drought tolerance
(iii) Triticale (6n) is a hybrid of wheat and rye. To make this plant fertile polyploidy is induced. It has higher dietary fibre and protein.
(iv) Raphano brassica is a allotetraploid by colchicine treatment.

Selection is one of the oldest methods of plant breeding in which individual plants or groups of plants are sorted out from a mixed population based on the morphological characters.
Methods of selection:
There are three methods of selection. They are
a) Mass selection
b) Pure line selection
c) Clonal selection
a) Mass selection:
(i) Seeds of best plants showing desired characters are collected from a mixed population.
(ii) The collected seeds are allowed to raise the second generation. This process is carried out for seven or eight generations.
(iii) At the end, they will be multiplied and distributed to the farmers for cultivation. Eg: Groundnut varieties like TMV-2 and AK-10.
b) Pureline selection :
(i) Pureline is "the progeny of a single individual obtained by self breeding":
(ii) This is also called as individual plant selection. In pureline selection large numbers of plants are selected from a self pollinated crop and harvested individually.
(iii) Individual plant progenies from them are evaluated separately. The best one is released as a pureline variety.
(iv) Progeny is similar both genotypically and phenotypically.
c) Clonal selection:
(i) A group of plants produced from a single plant through vegetative or asexual reproduction are called clones.
(ii) All the plants of a clone are similar both in genotype and phenotype.
(iii) Selection of desirable clones from the mixed population of vegetatively propagated crop is called clonal selection.