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The plastids heredity
The cytoplasm genetic continuity of organelles was first established for plastids. Many plant species are individuals deprived of color, or those in which the leaves have some unpainted areas of tissue. Their cells have no visible plastids or contain plastids not able to form chlorophyll. Plants deprived of greenness - albinos are not viable and usually die in the phase of the seedlings. But some parts of the tissue without a green color develops in the green leaf, feeding on through normal tissue, which supply their by products of photosynthesis.
In many cases, changes in the structure and function of plastids associated with mutations in one of the chromosomal gene. In maize, barley and other crops studied numerous chlorophyll mutation is inherited by the rules of Mendel. Often, however, the inheritance of such changes are not subject to the laws of Mendel, and it can only be explained on the basis of the concept of genetic continuity of plastids. Using electron-microscopic and autoradiographic methods was proved the existence of plastid DNA-containing areas. They are specific ribosome. Green plastids are able to synthesize DNA, RNA, and protein.
The plants of four-o'clock plant have a variegated variety. At one and the same plant, along with green branches are branches with leaves on which green tissue alternates with colorless stripes and spots. The flowers on the green branches of the variegated plants no matter what pollen pollinate them, provide seeds that always grow normal green plants. Seeds from the branches, the leaves which have no green color, give unpainted non-green sprouts. From seed, knot in variegated shoots, give mixed in various ratios offspring, consisting of green, variegated plants and unpainted.
A similar phenomenon was observed in variegated plants of snapdragons, pelargonium, evening primrose, plantain. These facts can be explained by assuming that the variegated plants have two types of plastids: normal and abnormal, is not able to form chlorophyll. During the multiplication of the normal are formed normal plastids, but from abnormal - abnormal (white) plastids. Of the ovule, which includes both types of plastids by mitotic divisions formed egg carrying only white or both simultaneously plastids.
One-sided, only through the maternal line, the transfer of the traits associated to the example of reciprocal crosses variegated plants and normal green plants. Variegated plant, if it is taken as the parent form, forms three types of eggs: with green, white and mixed plastids. Because of his father's sperm green leaves plant plastids do not contain such crossing will mixed offspring, in which a number of different plants will be determined by the random of the distribution of plastids during macrosporogenesis. In backcross green plant will form an egg with green plastids. Variegated plants are fertilized by sperm, they will give offspring, consisting only of plants with green leaves. Consequently, for reciprocal crosses between normal green plants or flowers with normal green variegated shoots and flowers from plants or shoots carrying abnormal plastids, plastid type and the nature of the offspring is determined by the parent form. Normal mother plant provides only normal offspring, and abnormal - just abnormal phenotype regardless of the paternal form.
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