File:Human idiogram-chromosome 21.jpg

Human Idiogram - Chromosome 21

Idiogram (karyogram) - A drawing or photograph of the chromosomes of a particular cell.

Links: chromosome 21 idiogram | Genome View - chromosome 21 | Trisomy 21 | Image - T21 female karyotype | Image - T21 male karyotype

Chromosome 21

• the smallest human chromosome
• about 47 million base pair
• about 1.5 % of the total DNA in cells
• contains between 300 and 400 genes (of human estimated 20,000 to 25,000 total genes)
• trisomy 21 or Downs Syndrome - additional copy of this chromosome
• partial monosomy 21 - missing segment of the chromosome in each cell
• ring chromosome 21 - circular structure, occurs when there are two breaks in a chromosome and the ends of the chromosome then fuse together

Idiogram Chromosome Banding - The term refers to the light and dark pattern, seen after staining with a dye, of individual chromosomes identified in metaphase. It is only in meiosis and mitosis during metaphase that chromosomes can be easily identified, during the normal cell life (interphase) the chromosomes are unravelled and distributed within the nucleus in chromosome territories. A band is that part of a chromosome which is clearly distinguishable from nearby regions by appearing darker or brighter with one or more banding techniques.

Human Idiogram: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | X | Y

Genetic abnormality locations: 1-4 | 5-8 | 9-12 | 13-16 | 17-20 | 21-XY

Inheritance Pattern images: Autosomal dominant inheritance | Autosomal recessive inheritance | X-Linked dominant (affected father) | X-Linked dominant (affected mother) | X-Linked recessive (affected father) | X-Linked recessive (carrier mother) | Mitochondrial genome inheritance | Codominant inheritance | Genogram symbols | Genetics

Links: Genetics | Abnormal Development - Genetic