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tissue culture hybridization


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tissue culture hybridization

  1. 2. The process of combining different varieties or species of organisms to create a hybrid. Hybrid refers to offspring resulting from the interbreeding between two animals or plants of different taxa.
  2. 3. <ul><li>Depending on the parents, there are a number of different types of hybrids; </li></ul><ul><li>Single cross hybrids  — result from the cross between two true breeding organisms and produces an F1 generation called an F1 hybrid (F1 is short for Filial 1, meaning &quot;first offspring&quot;). The cross between two different homozygous lines produces an F1 hybrid that is heterozygous; having two alleles, one contributed by each parent and typically one is dominant and the other recessive. The F1 generation is also phenotypically homogeneous, producing offspring that are all similar to each other. </li></ul><ul><li>Double cross hybrids  — result from the cross between two different F1 hybrids. </li></ul><ul><li>Three-way cross hybrids  — result from the cross between one parent that is an F1 hybrid and the other is from an inbred line. </li></ul><ul><li>Triple cross hybrids  — result from the crossing of two different three-way cross hybrids. </li></ul><ul><li>Population hybrids  — result from the crossing of plants or animals in a population with another population. These include crosses between organisms such as interspecific hybrids or crosses between different races. </li></ul>
  3. 4. Interspecific hybrids Sterility is often attributed to the different number of chromosomes the two species have, for example donkeys have 62 chromosomes, while horses have 64 chromosomes, and mules and hinnies have 63 chromosomes. Mules, hinnies, and other normally sterile interspecific hybrids cannot produce viable gametes, because, the extra chromosome cannot make a homologous pair at meiosis, meiosis is disrupted, and viable sperm and eggs are not formed.  Interspecific hybrids are bred by mating two species, normally from within the same genus. The offspring display traits and characteristics of both parents. The offspring of an interspecific cross are very often sterile; thus, hybrid sterility prevents the movement of genes from one species to the other, keeping both species distinct.
  4. 6. <ul><li>Zebroids </li></ul><ul><li>Zeedonk or Zonkey, a zebra/donkey cross. </li></ul><ul><li>Zorse, a zebra/horse cross </li></ul><ul><li>Zony or Zetland, a zebra/pony cross </li></ul>
  5. 7. Ligers and Tiglons (crosses between a lion and a tiger) and other Panthera hybrids such as the lijagulep. Various other wild cat crosses are known involving the lynx, bobcat, leopard, serval, etc.
  6. 8. Wholphin, a fertile but very rare cross between a false killer whale and a bottlenose dolphin. Cage bird breeders sometimes breed hybrids between species of finch, such as goldfinch x canary. These birds are known as mules.
  7. 9. Dzo, zo or yakow; a cross between a domestic cow/bull and a yak. The red wolf is considered by some to be a coyote/wolf hybrid.
  8. 10. A Cama is a hybrid between a camel and a llama. They are born via artificial insemination due to the huge difference in sizes of the animals which disallow natural breeding. A Cama usually has the short ears and long tails of a camel but the cloven hooves of a llama. Also most noticeably is the absence of the hump.
  9. 11. Crop yields increase dramatically when hybridization is used to exceed one or more of the parents in size and reproductive potential. Plants hybridize much more frequently and successfully than animals do. Pollen from flowering plants disperses widely and may land on flowers of other species. Chromosomal doubling (polyploidy) occurs more frequently in plants and facilitates the fertility of the hybrid offspring. Finally, plant forms are less stringently controlled than animal forms, and so the intermediate form of a plant hybrid is more likely to be physiologically successful.
  10. 13. Recently DNA analysis of a bear shot by a hunter in the North West Territories confirmed the existence of naturally-occurring and fertile grizzly–polar bear hybrids. There have been reports of similar supposed hybrids, but this is the first to be confirmed by DNA analysis. In 1943, Clara Helgason described a male bear shot by hunters during her childhood. It was large and off-white with hair all over its paws. The presence of hair on the bottom of the feet suggests it was a natural hybrid of Kodiak and Polar bear.
  11. 14. Consequences Hybridization can be a less discussed way toward Extinction then within detection of where a population lies along the hybrid continuum. The dispute of hybridization is how to manage the resulting hybrids. When a population experiences hybridization with substantial introgression, there still exists parent types of each set of individuals. When a complete hybrid swarm is created, all the individuals are hybrids.
  12. 15. Ma nagement of h ybrids Cons erv ationists disagree on when is the pr ope r time to give up on a population that is becoming a hybrid swarm or to try and save the still existing pure individuals. Once it becomes a complete mixture, we should look to conserve those hybrids to avoid their loss. Most leave it as a case-by-case basis, depending on detecting of hybrids within the group. It is nearly impossible to regulate hybridization via policy because hybridization can occur beneficially when it occurs &quot;naturally&quot; and there is the matter of protecting those previously mentioned hybrid swarms because if they are the only remaining evidence of prior species, they need to be conserved as well.