Five necessary attributes

General adaptability to the environment. 

High searching capacity for hosts. 

High rate of increase relative to the hosts. 

Good dispersal ability. 

Minimal time lag effects in responding to changes in host numbers.

TLS Online TPP Program

#Id: 4043

#Unit 2. Cellular Organization

When mitotic chromosomes are subjected to proteolytic enzyme (trypsin) treatment followed by staining with the chemical dye Giemsa, they generate distinct chromosome-specific patterns called G-bands.

p (short; after the French petit) or q (long; for queue, the French word for tail)

TLS Online TPP Program

#Id: 4044

#Unit 2. Cellular Organization

In G-banding, chromosomes are first gently heated and then exposed to Giemsa stain; this DNA dye preferentially darkens certain regions to produce alternating dark and light G bands. Each G band is a very large segment of DNA from 1 to 10 Mb in length, containing many loops. With high-resolution G-banding techniques, a standard diploid human karyotype of 46 chromosomes is seen to contain hundreds of dark and light G bands. Not used in plants.

TLS Online TPP Program

#Id: 4045

#Unit 2. Cellular Organization

G-bands are distinguished from interbands by their lower G-C content. This is a peculiar result. If there are 10 bands on a large chromosome with a total content of 100 megabases (Mb), this means that the chromosome is divided into regions of 5 Mb in length that alternate between low G-C (band) and high G-C (interband) content.

There is a tendency for genes to be enriched in the interband regions.

TLS Online TPP Program

#Id: 4046

#Unit 2. Cellular Organization

In the case of human chromosomes, approximately 300 G bands can usually be distinguished during metaphase. A larger number of G bands (in the range of 800) can be observed in prometaphase chromosomes because they are more extended than metaphase chromosomes.

TLS Online TPP Program

#Id: 4047

#Unit 2. Cellular Organization

Heterochromatic regions, which tend to be rich with adenine and thymine (AT-rich) DNA and relatively gene-poor, stain more darkly in G-banding.

In contrast, less condensed chromatin (Euchromatin)—which tends to be rich with guanine and cytosine (GC-rich) and more transcriptionally active—incorporates less Giemsa stain, and these regions appear as light bands in G-banding.

TLS Online TPP Program

#Id: 4048

#Unit 2. Cellular Organization

Chromatin Immunoprecipitation (ChIP) is same as Chromosome Conformation Capture.

3C assays involve three basic steps:

(1) interacting chromosome segments are cross-linked with formaldehyde, 

(2) the DNA is digested, and

(3) cross-linked DNA fragments are ligated to produce products that are amplified and can be further analyzed.