Changes

Cell division is arrested during metaphase, when the chromosome material is condensed. Following hypotonic treatment and fixation, the cells are dropped on a slide and then stained. At least 20 metaphase spreads are analyzed and 2 or 3 metaphase spreads are photographed. The chromosomes are arranged from largest to smallest to create a karyotype.  

Cell division is arrested during metaphase, when the chromosome material is condensed. Following hypotonic treatment and fixation, the cells are dropped on a slide and then stained. At least 20 metaphase spreads are analyzed and 2 or 3 metaphase spreads are photographed. The chromosomes are arranged from largest to smallest to create a karyotype.  

Chromosomes vary in size and in shape. The pairs of [[autosomal chromosomes]] are arranged in a karyotype from the biggest to the smallest. The [[sex chromosomes]] are placed to the right of the smallest [[autosomal chromosomes]]. Chromosomes vary in shape depending upon the position of the [[centromere]], the structure that holds the two arms of the chromosomes together. If the [[centromere]] is in the middle, the chromosome is metacentric and the chromosome arms are equal in size. If the centromere is off center, the chromosome is submetacentric with a short arm labeled p (for petite) and a long arm labeled q (the next letter after p). If the centromere is close to the end, the chromosome is acrocentric and the very short arm consists of a stalk and a knob (satellite). Based upon size and shape, human chromosomes are divided into eight groups: A (1 to 3), B (4 and 5), C (6 to 12), D (13 to 15), E (16 to 18), F (19 and 20), G (21 and 22) and the sex chromosomes, XX in females and XY in males.  

Chromosomes vary in size and in shape. The pairs of [[Autosome|autosomal chromosomes]] are arranged in a karyotype from the biggest to the smallest. The [[sex chromosomes]] are placed to the right of the smallest autosomes. Chromosomes vary in shape depending upon the position of the [[centromere]], the structure that holds the two arms of the chromosomes together. If the [[centromere]] is in the middle, the chromosome is metacentric and the chromosome arms are equal in size. If the centromere is off center, the chromosome is submetacentric with a short arm labeled p (for petite) and a long arm labeled q (the next letter after p). If the centromere is close to the end, the chromosome is acrocentric and the very short arm consists of a stalk and a knob (satellite). Based upon size and shape, human chromosomes are divided into eight groups: A (1 to 3), B (4 and 5), C (6 to 12), D (13 to 15), E (16 to 18), F (19 and 20), G (21 and 22) and the sex chromosomes, XX in females and XY in males.  

Chromosomes are further identified by banding patterns created by specialized staining procedures to produce G bands, R bands, C bands, etc. The choice of staining procedure depends upon the information that is desired. Most commonly, chromosomes are stained with trypsin-Giemsa to produce the G-banded pattern. The banding pattern is determined by the degree of chromatin condensation and the specific DNA-protein present at the different sites on the chromosome. These banding patterns are distinct and consistent for each chromosome. Thus, one can reliably identify the chromosome pairs (e.g., although of the same size and shape, the six acrocentric chromosomes in the D group can be differentiated into pairs 13, 14 or 15 based upon banding patterns). The bands are individually numbered (e.g., 11q23 refers to band #23 on the long arm q of chromosome #11). :<ref>http://www.vivo.colostate.edu/hbooks/genetics/medgen/chromo/cytotech.html</ref>

Chromosomes are further identified by banding patterns created by specialized staining procedures to produce G bands, R bands, C bands, etc. The choice of staining procedure depends upon the information that is desired. Most commonly, chromosomes are stained with trypsin-Giemsa to produce the G-banded pattern. The banding pattern is determined by the degree of chromatin condensation and the specific DNA-protein present at the different sites on the chromosome. These banding patterns are distinct and consistent for each chromosome. Thus, one can reliably identify the chromosome pairs (e.g., although of the same size and shape, the six acrocentric chromosomes in the D group can be differentiated into pairs 13, 14 or 15 based upon banding patterns). The bands are individually numbered (e.g., 11q23 refers to band #23 on the long arm q of chromosome #11). :<ref>http://www.vivo.colostate.edu/hbooks/genetics/medgen/chromo/cytotech.html</ref>

[[Category:Biology]]

[[Category:Biology]]