Chromosomes

Prokaryotic chromosomes The prokaryotic DNA (bacterias) is a molecule, a circular chromosome, floating freely in the cytoplasm and without nuclear membrane.

Eukaryotic chromosomes The eukaryotic chromosomes contain the genetic information in all eukaryotic Mainly all the eukaryotic organisms have between 10 and 50 chromosomes in their body cells. The human cells have 46 chromosomes (23 identical pairs).

¿Do all the living thins have the same number of chromosomes?? No. Each species have a characteristic chromosomes number. For example:

Eukaryotic chromosomes Each chromosome is made up of an only DNA molecule, strongly twisted around. Chromosomes can’t be seen when the cell is not dividing. At that moment we call it chromatin.

Chromosomes in division cells Each chromosome is composed of two sister chromatids, which are attached at a central point, the centromere. Sister chromatids

Elements of the chromosomes

centromers Sister chromatids

Kinetochore Chromatid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Metaphase chromosome Kinetochore microtubules Centromere region of Chromatid

Different types of chromosomes according the centromere:

Karyotipe of a human being

Karyotipe The set of chromosomes ordered according to their size and the position of their centromeres. First 22 pairs are called autosomes. The last pair is the sex chromosomes. XX female and XY male.

The Y chromosome decision Boy or girl? The Y chromosome decision Y - Chromosome X - Chromosome

Woman karyotipe XX decide female sex

Men karyotipe XY decide male sex

Changes in the karyotipe This karyotipe have 3 number 21chromosomes. This disorder is characterystic of Down syndrome (trysomy 21).