Mutation is a change in DNA in a plant that can be transmitted through its offspring. It is a rare process taking place with a frequency of about 1 in 100,000. DNA in plants can be found in the nucleus, in chloroplasts and in mitochondria. The mutation can take place in a leaf bud during mitose (a somatic mutation) resulting usually in a change in part of an organism. A mutation in the flower during meiose (pollen or egg cell formation) leads to a change in the whole plant (usually visible only in the second generation).
Mutations can also be divided into two types: nuclear mutations that inherit via both parents, and cytoplasmic mutations i.e., in the DNA of chloroplast or mitochondria that only can be transmitted via the mother (seedparent). If a leaf changes from green to yellow it can be caused indirectly by a nuclear mutation (as is usually the case in hostas) or directly by a mutation in the chloroplast DNA. So the fact that the chloroplast is in the cytoplasm does not mean that a change in its color always gives a non-mendelian inheritance. On the contrary in hostas the change from green to yellow is nearly always due to a nuclear mutation. Without mutation there is no variegation.
When a mutant mutates back to wildtype, such is backmutation. Contrary to generally held opinions, back mutations are as rare as forward - (new) mutations. A yellow-edged plant going back to all green is usually not a back mutation but a chimaeral rearrangement (see Below).
A yellow plant getting a green edge is not backmutated either (or rarely so) but rather is the result of recombination (see bolow).
Recombination or Crossing Over
In diploid plants (and except H. ventricosa and H. Clausa all wild hostas are diploid) each character (gene) is paired with another. If one of a gene pair is mutated usually we do not see anything unless the gene is dominant like most yellow genes in hostas; however, it is possible due to exchange (mitotic...
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