Standard content

A horse and a donkey can have a young one, the mule, and the mule cannot have young. So are the horse and the donkey one species or two? In this course we read three ideas that the main chapter only touches: what a species really is, the finer rules that give each species one name, and how a key and a DNA barcode find a name. Then we solve harder problems and take a NEET style test.

What's inside

1. Extended reading: what is a species?: The main chapter says that a species is a group with fundamental similarities. The biological species concept adds that its members can interbreed and are reproductively isolated from other groups. It works well for animals that mate, and it fails for bacteria and for fossils. A subspecies is a regional form of one species and has a name of three words.
2. Extended reading: the finer rules of naming: A full zoological name carries the author and the year, for example Panthera leo (Linnaeus, 1758). Brackets show that the species was first described in another genus. Zoological names count from 1758 and botanical names from 1753. If one species has several names, the oldest valid name is used and the others are synonyms. Every name is tied to a type specimen, such as a holotype, kept in a museum or a herbarium.
3. Extended reading: counting a key, and DNA barcodes: A key for n species needs n − 1 couplets, because each couplet splits one group into two. A chain key may ask up to n − 1 questions, and a balanced key asks at most the next whole number above log₂ n. A DNA barcode is a short stretch of DNA, for animals about 650 base pairs of the gene COI, used as a label. With 4 bases and n positions, there are 4ⁿ different sequences.