Crossbreeding (genetics)

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Crossbreeds of different cattle breeds are very successful in Namibia . Here between Brahman , Hereford , Simbra and Brown Swiss

Crossbreeding is a term used in genetics. In plants and animals , on the one hand, the sexual reproduction between two genetically different but relatively closely related species , subspecies or varieties (in plants) or races (in animals) is referred to, and on the other hand their result is called crossbreeding. Deviating from this usage, the term is used in fungi for any sexual reproduction in which haploid individuals of different types of crosses produce diploid spores. A cross here is any sexual reproduction with the participation of compatible, genetically different, (heterothallic) individuals, whereby there can be far more such cross-breeding types than the usual two sexes.

In the case of plants and animals, the terms crossbreeding and crossing usually refer to controlled reproduction in the context of breeding or crossbreeding experiments . The “natural crossing” of different genetic lines through the hybrid with mixed traits, i.e. H. intermediate properties that arise is usually called hybridization. Both in natural populations and in breeding, a possibly unusual and rare hybridization with subsequent backcrossing with one of the parent species is important, so that genetic material can be transferred from the second line to the first; this is called introgression .

Crossings are usually possible without any problems within a biological species. When crossing different species (interspecific crossing), crossing barriers can often be observed which make crossing difficult or impossible. Under certain circumstances it is only possible in one direction, with female germ cells of one type and male of the other type, while crosses in the other direction are unsuccessful. These crossing barriers lead to (reproductive) isolation , in population genetics and evolutionary biology one speaks of isolation mechanisms . Populations without crossing barriers between them form a common gene pool .

Humans have been using crossbreeding in breeding for thousands of years to create new species, plant varieties or breeds of farm animals (ie "crossbreeds"). The descendant from a cross of individuals that can belong to different species (very rarely even different genera ), subspecies or breeding lines is called a hybrid .

Gregor Mendel showed the first laws in the inheritance of properties in 1865. The results of his cross-breeding experiments with pea plants led him to the realization that the inheritance of traits can be described in the form of mathematical proportions. These Mendelian inheritance rules are still applicable today. They went down in history as the basis of genetics . The crossing experiments were extended by Thomas Hunt Morgan with experiments on the fruit fly Drosophila melanogaster . With the help of this knowledge, he was able to build a gene map .

Web links

Individual evidence

  1. Duden online: crossing (see meaning 2 a) and crossing (see meaning 7)
  2. 'Crossing' in the compact lexicon of biology .
  3. ^ Duden online: crossing (see meaning 2 b).
  4. Hans Günter Schlegel: General Microbiology. Thieme-Verlag, 2007. ISBN 978-3-13-444608-1 . on page 68.
  5. Duden online: crossing (see “breeding result”) and crossing (see explanation “for the purpose of breeding”).