Seminario 17 Características de los Cromosomas y Técnicas de citogenética - Rodolfo Rey

Hello, my name is Rodolfo Rey and I welcome you to this molecular biology and genetics class on the characteristics of human chromosomes and classical cytogenetic techniques . In this class we will review the concept of chromosome, the states of chromatin and the cell cycle. We will look at the different types of chromosomes, what

the human karyotype is like and the nomenclature used, and how chromosomal material is studied, its usefulness and the fundamentals of classical and molecular cytogenetic techniques with a focus on banded karyotyping, high-resolution karyotyping and in-situ fluorescent hybridization or fish. We then begin by reviewing what we already know about chromatin and the patterns of

DNA coiling to form a chromosome. As you know, double helix DNA wraps around histones, thus forming nucleosomes. These in turn coil up forming the solenoid fibers that will eventually give rise to the chromatin loops. DNA, if stretched out in an average cell, would measure approximately 2 m in a human cell. Around each nucleodystone there are

approximately 140-150 DNA bases that make up a nucleosome. As we see here, 20 or 60, between 20 and 60 bases further on, that is, there is a spacer before the next nucleosome. Approximately six nucleosomes make up a helical solenoid. The helical solenoids in turn are organized into chromatin loops that are attached to a

protein scaffold. Each loop of chromatin contains approximately 100,000 base pairs or 100 kbases 100 cab. of DNA. Thus, the DNA of a condensed cell, with all these structures we mentioned, measures approximately 10,000 times less than if it were stretched out, that is, approximately 0.2 mm or 200 micrometers. What is the state of chromatin at different