There are two biological definitions, the classical definition via interfertility
of individuals, and the more recent, based on DNA comparison.
of races, their morphological similarity and occasional co-occurrence on the same host species do not support the idea of distinct parasite species.
However, says Kadar, if an HSP60 test could predict interfertility
as well as the risk of ectopic pregnancy, in many cases it could allow women to bypass the elaborate and costly techniques now used to diagnose infertility.
Differences in reproductive biology, including pollination ecology, degree of self-fertility, and interfertility
relationships all can influence levels of reproductive isolation and can affect patterns and levels of genetic diversity within and among populations (Arnold et al.
These boundary arrangements are distributed such that they enable full interfertility
between adjacent populations (Bloom and Lewis 1972).
Morphometric differentiation, patterns of interfertility
, and the genetic basis of character evolution in Crepis tectorum (Asteraceae).
In palaeontology interfertility
criteria are unusable, and DNA sequencing is very controversial at best, so morphometrics is one of the only ways to reconstruct a supposed genealogical tree of each species by allowing at least the comparison of morphological spaces.
The use of a crop domestication model provides a foundation for the conclusion that breeding by hybridization with the mentioned and other species is justified, while study of chloroplast DNA variation may play an important role in indicating the level of interfertility
in this crop.