Carbon Dioxide Sensitivity in Drosophilla
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This document discusses CO2 sensitivity in Drosophila flies. It notes that while most Drosophila are not affected by exposure to CO2, a sensitive strain was discovered that becomes paralyzed upon brief exposure. Sensitivity is inherited maternally, being passed from females to their offspring but rarely from males. The document further explains that sensitivity in this strain is caused by a virus-like particle called sigma found in the fly's cytoplasm, and can be transmitted to normal flies by injection of extract from sensitive flies. Sigma is dependent on temperature and initial levels for its reproduction. It is a non-chromosomal, cytoplasmic element that can induce sensitivity regardless of the fly's genetic makeup.
Carbon Dioxide Sensitivity in Drosophilla
- 1. co2 SENSITIVITY IN DROSOPHILA ANJALI RAJPUT RIYA GAUTAM B.SC. B.ED. BIO(3 SEM)
- 2. CO2 SensitivityinDrosophila 1.MOST DROSOPHILA FLIES, CAN BE SUBJECTED TO A CONTACT WITH PURE CO2 FOR LONG HOURS, WITHOUT INJURY. 2.L'HERITIER AND TEISSER (1958), HOWEVER, DISCOVERED A TRUE BREEDING STRAIN OF DROSOPHILA WHICH WAS SENSITIVE TO CO2. 3.THE SENSITIVE FLIES, WHEN EXPOSED BRIEFLY TO CO2 FOR A SHORT PERIOD, BECOME UNCONSCIOUS IN A CHARACTERISTIC WAY, WITH THEIR LEGS BECOMING PARALYSED. 4.WHEN RECIPROCAL CROSSES WERE MADE BETWEEN CO2 SENSITIVE AND NORMAL STRAINS, IT COULD BE SHOWN THAT THE TRAIT WAS INHERITED ONLY FROM FEMALE PARENT. IN OTHER WORDS, WHILE SENSITIVE MOTHERS ALWAYS GIVE SENSITIVE PROGENY, SENSITIVE FATHERS ONLY RARELY GIVE SENSITIVE PROGENY IF THE MOTHER IS NORMAL. 5. IN RARE TRANSMISSION THROUGH MALE ALSO, SENSITIVITY IS QUICKLY LOST AFTER FIRST GENERATION.
- 3. 6.It has also been shown that if an extract obtained by crushing sensitive flies, is injected into the body of wild (normal) flies, sensitivity can be induced. It was also shown that this sensitivity can be attributed to a virus like particle called sigma found in cytoplasm of the cells of a sensitive fly.
- 4. *sigma factor : Sigma factor is transmitted through egg cytoplasm and its reproduction depends on initial supply and on suitable temperature of 20°C, because it is labile at high temperature. It does not need a specific gene and may be found associated with different genotypes. A sensitive fly retains its sensitive trait, even when all its chromosomes are replaced by those of normal fly, suggesting that sigma factor or particle is in cytoplasm and has properties of non-chromosomal genes or plasma genes. Some physical characteristics of sigma are also known. It seems to be a particle 0.07 micron in diameter, and contains DNA responsible for its hereditary nature.
- 5. Let me tell you something about cytoplasmic inheritance: (it could be shown that the trait was inherited only from female parent. Sigma factor is transmitted through egg cytoplasm) Chromosome theory of inheritance suggested that Mendelian factors or genes were located on chromosomes. Since chromosomes divide in a very precise manner both during mitosis as well as during meiosis, it is easy to draw a parallelism between chromosomes and genes. Cytoplasm, however, does not divide in such a precise manner during cell division. Female gamete usually contributes more cytoplasm to the zygote. Inheritance in these cases would be mainly of maternal type, for example: As can be seen in the figure, if two strains A and B respectively having genotypes AA and BB and cytoplasms a and b are crossed reciprocally, we will get two hybrids AB (a) and AB (b) (cytoplasm is indicated in parentheses).
- 6. In case of maternal effect, AB (a) and AB (b), despite having same nuclear genotype will differ. AB (a) will resemble strain A or AA (a) and AB (b) will resemble strain B or BB (b). - Since such effects are solely produced by cytoplasm of the egg, they are described as maternal effects. - However, maternal effects are often produced due to effect of genes through cytoplasm. In other words, properties of cytoplasm depend on nuclear genes. - Such cases can be distinguished from those, where extrachromosomal or cytoplasmic hereditary units are present and function either independently or in collaboration with nuclear genetic system. This is called extrachromosomal or cytoplasmic inheritance.
- 7. We know that in chromosomes, DNA is the sole genetic material and is the storehouse of genetic information. Discoveries of presence of DNA in cell organelles found outside the nucleus is a strong evidence to suggest that genetic information does exist in cytoplasm also. two important and organelles i.e. plastids (in plants only) and mitochondria located in cytoplasm carry DNA. These organelles control extrachromosomal inheritance in many cases through their DNA, which carries genetic information. However, there are other cases, where cytoplasmic inheritance depends on extra-chromosomal particles, which are not essential for cell function and, therefore, may be present or absent Such dispensable particles include kappa in Paramecium, and sigma in Drosophila. These particles are not only inherited but are also infective, since they can be introduced into new hosts without the need of actual process of reproduction.
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