MAINTENANCE OF CYTOGENETIC STOCKS AND THEIR IMPORTANCE

Genetic stocks are lines that contain various mutant alleles, chromosomal rearrangements, or other cytological abnormalities that are useful only for genetic and basic biological experiment.

Genetic stocks

OTHER CLASSES OF ORGANISMS

• Coliform bacterium Escherichia coli

• Pink bread mold Neurospora crassa

• Fruit fly Drosophila melanogaster

They have no direct economic benefit but that are used solely for the purposes of research and teaching .

Genetic stocks can be divided into three general groups:

Cytological stocks (e.g. chromosome addition/substitution, aneuploids)

Mutants (e.g induced/insertion mutants, tilling populations)

Germplasm sets (e.g. mapping populations, parental lines, reference germplasm)

Cytogenetic StockCytogenetic stocks are desired chromosome , aneuploidy lines

that are useful for genetic and basic biological experiment.

Variants with different chromosome structures.

Variants in chromosome number.

Alien and substitution lines.

With Different chromosome structures.Due to..

Deletion Duplication

Inversion

translocation of specific DNA segments from one chromosome to another

They are important in gene mapping, determination of the chromosomal location of specific genes, and studies of chromosome structure and function.

variants in chromosome number These may include.. changes in whole genomes of plants(haploids or

polyploids)

changes in the number of a single chromosome, chromosome arm, or chromosome segments (nullisomics, monosomics, telosomics, trisomics, or tetrasomics).

Such variants are also valuable in genetic mapping and in basic genetic studies, such as in the study of genetic architecture of chromosomes.

Alien and substitution lines

The wild and the weedy relatives of the major crops are sometimes used as germplasm sources in breeding programs.

A first steps is often the transfer of individuals chromosomes or chromosome segments, carrying identified genes of potential economic importance into the crop species.

The types of alien chromosome segments used to transfer the desired gene into commercial crop varieties are addition lines, and translocation lines.

Aneuploidy

Is a second major category of chromosome mutations in which chromosome number is abnormal.

An aneuploid is an individual organism whose chromosome number differs from the wild type by part of a chromosome set .

Nullisomics (2n − 2) Monosomics (2n − 1) Trisomics (2n + 1)

A) ADDITIONS TO CHROMOSOME NUMBER:

Trisomy [2n + 1]: examples in humans include Klinefelters (XXY), and Down’s syndrome individuals [2n = 47D].

Tetrasomy [2n + 2]: examples are mostly in polyploid plants

B) REDUCTIONS IN CHROMOSOME NUMBER: Monosomy [2n – 1]: example in humans is

Turners (XO).

Nullisomics (2n − 2) Nullisomy is a lethal condition in diploids, an organism

such as bread wheat, which behaves meiotically like a diploid although it is a hexaploid, can tolerate nullisomy.

TRISOMICS (2N + 1)

The trisomic condition also is one of chromosomal imbalance and can result in abnormality or death.

Klinefelter syndrome (XXY)

IMPORTANCE AND USE OF GENETIC STOCK COLLECTIONS

1) To conserve both

Economically important species, corn (Zea mays) and yeasts (Saccharomyces sp.).

Organisms used purely for research such as fruit flies (Drosophila sp.) & bread molds (Neurospora sp.).

2) Used in mapping the genes.

3) Can preserve stocks for many years.

4) Helps in the identification, location, and isolation of specific genes and their manipulation and transfer into economically important plants and animals for breeding programs using molecular genetics tools.

5) Its helps in conserving endangered species.

6)These are used solely for genetic research and teaching.

7) Used for new hybrid production.

USE OF CYTOGENETIC STOCK COLLECTIONS Used to determine the phenotypic effects of loss or

gain of different chromosomes.

Used to produce chromosomal substitution lines.

Find the location of genes as well as of a linkage group onto a specific chromosome.

To Establish homoeology (by to study of nullisomic)

Used to identify the chromosomes ivolved in translocation.

Used to prepare molecular maps.

MAINTAINING GENETIC (or) CYTOGENETIC STOCKIt requires

Technical labours Scientific inputs Mechanised Tools Resources

The broad requirements include the following:

Suitable low-temperature, low-humidity facilities; Access to back-up storage facilities; Adequate seed-handling facilities for drying, cleaning,

packaging, and viability testing of seed samples; and Computerized information storage and retrieval systems.

Special Needs and Requirements Genetic stocks require highly specialized knowledge,

procedures, and care for adequate regeneration and maintenance.

Albino mutants are one obvious example. Some stocks may not routinely survive in the field and need to be grown in a greenhouse, whereas others may need special treatments (long days or vernalizing temperatures) before they flower or may require genetic or cytological screening.

Genetic stock collections are difficult, and sometimes impossible, to maintain as part of national or international germplasm collections.

EXAMPLES OF GENETIC STOCK COLLECTIONS

The Charles M. Rick Tomato Genetics Resource Center

Barley Genetic Stock Collections

The Barley Genetic and Aneuploid Stock

Collection

The Charles M. Rick Tomato Genetics Resource Center

Tomato Genetics Stock Center (TGSC)

Charles M. Rick of the Department of Vegetable Crops at the University of California, Davis

Davis is near the center of the largest tomato-growing area in the world, and in 1987 nearly one-quarter of the world's processing tomatoes were grown in eight counties within a 129-km radius of Davis.

Barley Genetic Stock Collections

Barley geneticists and breeders

Under this scheme, individuals are appointed to coordinate maintenance of each of the different categories of genetic and chromosomal variants commonly found in barley.

coordinators have been appointed for maintaining genetic stocks.

The Barley Genetic and Aneuploid Stock Collection

Barley Genetic and Aneuploid Stock Collection (BGASC)

was established by D. W. Robertson in the Agronomy Department at the Colorado State University, Ft. Collins

for genetic linkage studies in barley. These studies began in the 1920s and emphasized simple morphologic marker genes of value in early linkage studies

Over the years the collection was enriched by the addition of a wide range of naturally and artificially generated variants, linkage testers, and more recently, of cytogenetic stocks from the local program and others in the United States.