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The concept of cytoplasmic inheritance
Student: Yana Bortnyk
Group IES 204
Leader: Vasylchenko O.A
1. The concept of cytoplasmic inheritance.
2. Forms of cytoplasmic heredity.
2.1. The plastids heredity.
2.2. Cytoplasmic male sterility.
3. Extranuclear inheritance of organelles.
4. Extranuclear inheritance of parasites.
5. Types of extranuclear inheritance.
6. Emerging Discoveries in cytoplasmic inheritance.
The concept of cytoplasmic inheritance
The сhromosome theory of heredity has established a leading role of nuclei and containing in it chromosomes in the phenomena of heredity. But at the same time in the early years of formation of the science of genetics was know the facts, which show that the inheritance of certain traits associated with non-chromosomal components of the cell and does not obey to Mendel laws, based on the distribution of chromosomes during meiosis.
In 1908 - 1909 years. C. Correns and simultaneously E. Baur described the variegation in four-o'clock plant and snapdragon, which is inherited through the cytoplasm(Fig.1) In subsequent years similar observations have been made on other sites. All are correct interpreted as examples of cytoplasmic inheritance, but at least they have long regarded simply as individual deviations from the laws of Mendel.
Fig.1: Leaf variegation in Mirabilis Jalapa
Further study of the phenomena of heredity led to the need to establish not only the mechanism of gene transfer of chromosomes from one generation of organisms to another, but also how these genes control the processes of cell metabolism and the development of certain characters and properties. Therefore, the cell was seen as a single integrated system, which defines the transmission and reproduction traits in the offspring of resulting from the interaction nucleus components (genes of chromosomes) and the cytoplasm, which can be illustrated by acquiring of its ability to photosynthesize. Photosynthesis is associated with cytoplasmic structures of the cell – plastids and contained therein pigment chlorophyll. The formation and function of plastids are caused by hereditary factors and the influence of external conditions (mainly light, without which the chlorophyll in the plastids is not formed). Mutations in certain chromosomal loci can be partially or completely disrupt the formation of plastids and they contain chlorophyll. These so-called chlorophyll mutations are inherited, strictly obeying the laws of Mendel. But abnormal (white) plastids can form in cells with a normal set of genes, and in good light. This feature is not inherited by the rules of Mendel. During cell division, comprising said abnormal plastids formed daughter cells with the same plastids, but when crossed this trait is transmitted only through the maternal line, and, therefore, it is not associated with the chromosomes, but with the cytoplasm. Thus, the most important property of the cell - its ability to photosynthesize - is determined by the interaction of genes of chromosome structural elements of the cytoplasm and the external environment.
Genetic material of chromosomes (genome) corresponds to the plasmon, which includes all the genetic material of the cytoplasm. Like genes of chromosomes in the structural elements of the cytoplasm - plastids, Basal bodies, mitochondria, centrosomes and plasmides is material carriers of extrachromosomal heredity - plasminogen. They can determine the development of some signs of a cell, capable of doubling their reproduction, during the dividing of the mother cell they are distributed between daughter cells.
It is possible that the cytoplasmic heredity is also due to long-lived molecules mRNA and the selective transcription of mRNA molecules only from genes of maternal chromosomes. The best studied two forms of cytoplasmic inheritance: plastid and cytoplasmic male sterility.
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