Character displacement

Morphological differences in two closely related species present in same geographical area while similar morphology when present at different geographical are

1. Niche diversification

2. Co-existence of many species

3. Evolutionary program

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.

TLS Online TPP Program

#Id: 4049

#Unit 2. Cellular Organization

This is used to identify when regulatory proteins bound at an enhancer are in close proximity to the transcriptional machinery at a given promoter—a physical proximity interpreted to show looping out of the DNA

TLS Online TPP Program

#Id: 4050

#Unit 2. Cellular Organization

The interphase nuclei of some tissues of the larvae of dipteran flies contain chromosomes that are greatly enlarged relative to their usual condition. They possess both increased diameter and greater length. shows an example of a chromosome set from the salivary gland of D. melanogaster. The members of this set are called polytene chromosomes.