Editing Hybrid (biology) (section)

===Mechanisms of reproductive isolation===
{{main|Reproductive isolation}}

Interspecific hybrids are bred by mating individuals from two species, normally from within the same genus. The offspring display traits and characteristics of both parents, but are often [[Sterility (physiology)|sterile]], preventing gene flow between the species.<ref>{{cite book |last=Keeton |first=William T. |date=1980 |title=Biological Science |location=New York |publisher=Norton |isbn=9780393950212 |page=800}}</ref> Sterility is often attributed to the different number of chromosomes between the two species. For example, [[donkey]]s have 62 [[chromosomes]], [[horse]]s have 64 chromosomes, and [[mule]]s or [[hinny|hinnies]] have 63 chromosomes. Mules, hinnies, and other normally sterile interspecific hybrids cannot produce viable gametes, because differences in chromosome structure prevent appropriate pairing and segregation during [[meiosis]], meiosis is disrupted, and viable sperm and eggs are not formed. However, fertility in female mules has been reported with a donkey as the father.<ref>{{cite journal |pmid=3378453 |date=1988 |last1=Rong |first1=R. |last2=Chandley |first2=A. C.|last3=Song |first3=J. |last4=McBeath |first4=S. |last5=Tan |first5=P. P. |last6=Bai |first6=Q. |last7=Speed |first7=R. M. |title=A fertile mule and hinny in China |journal=Cytogenetics and Cell Genetics |volume=47 |issue=3 |pages=134–9 |doi=10.1159/000132531}}</ref>

A variety of mechanisms limit the success of hybridization, including the large genetic difference between most species. Barriers include morphological differences, differing times of fertility, mating behaviors and cues, and physiological rejection of sperm cells or the developing embryo. Some act before fertilization; others after it.<ref>{{cite journal |last1=Baker |first1=H. G. |date=1959 |title=Reproductive methods as factors in speciation in flowering plants |journal=Cold Spring Harb Symp Quant Biol |volume=24 |pages=177–191 |doi=10.1101/sqb.1959.024.01.019 |pmid=13796002}}</ref><ref>{{Cite journal |doi=10.1038/hdy.1986.135 |last1=Barton |first1=N. |last2=Bengtsson |first2=B. O. |date=1986 |title=The barrier to genetic exchange between hybridising populations |journal=Heredity |volume=57 |issue=3 |pages=357–376 |pmid=3804765 |s2cid=28978466 |doi-access=free|bibcode=1986Hered..57..357B }}</ref><ref>{{cite book |last=Strickberger |first=M. |date=1978 |title=Genética |language=es |publisher=Omega |location=Barcelona |pages=874–879 |isbn=9788428203692}}</ref><ref>{{cite book |last=Futuyma |first=D. |date=1998 |title=Evolutionary Biology |edition=3rd |publisher=Sinauer |location=Sunderland}}</ref>

In plants, some barriers to hybridization include blooming period differences, different pollinator vectors, inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and structural differences of the chromosomes.<ref>{{cite journal |last1=Hermsen |first1=J. G. Th. |last2=Ramanna |first2=M. S. |title=Barriers to hybridisation of ''Solanum bulbocastanum'' Dun. and ''S. Verrucosum'' Schlechtd. and structural hybridity in their F1 plants |journal=Euphytica |volume=25 |number=1 |date=January 1976 |doi=10.1007/BF00041523 |pages=1–10|bibcode=1976Euphy..25....1H |s2cid=37518270}}</ref>