Chromosomes and karyotype

In short: Chromosomes are thread-like structures in the cell nucleus that package an organism’s DNA in an organized way. The karyotype describes the number, size, and shape of all of an organism’s chromosomes.

In more detail: Humans have 46 chromosomes arranged in 23 pairs, 22 of which are matching autosomes and one pair is the sex chromosomes.

In detail

• Structure: A chromosome consists of DNA tightly wound around histone proteins, allowing the genetic material to be packaged compactly.
• Chromosome pairs: One chromosome comes from the mother, the other from the father; together they form a homologous pair.
• Sex chromosomes: XX determines female sex in humans, XY male, with the Y chromosome being noticeably smaller.
• Karyogram: A photographic representation of all chromosomes in a cell nucleus, arranged by size, used to diagnose chromosomal disorders.
• Trisomies: An extra chromosome, as in trisomy 21 (Down syndrome), usually arises from an error during cell division (mitose-und-meiose).
• Species comparison: Chromosome number varies greatly between animal species and says nothing about an organism’s complexity.
• Condensation during division: During cell division, chromosomes visibly condense; outside of that, they exist as relaxed chromatin (dna-und-rna-unterschiede).