GENETICS/gene conversion/sister chromatid exchange..

Gene conversion is when the sequence of one region of DNA is used as a template to correct of modify the sequence of another region of DNA.

Sister chromatid exchange (SCE) involve breakage of both DNA strands, followed by an exchange of whole DNA duplexes. This occurs during S phase and is efficiently induced by mutagens that form DNA adducts or that interfere with DNA replication. The formation of SCEs has been correlated with recombinational repair and the induction of point mutations, gene amplification and cytotoxicity.

The double-strand break model of genetic recombination initiates exchanges by a double-strand break and results in two half chiasmas.

• In this model a double-strand break (1) initiates the process.
• The gap is extended by exonuclease action, a 5' exonuclease being more active and exposing 3'-unpaired ends (2).
• An unpaired 3' end invades the duplex DNA of the homologous chromosome (3) displacing one of the strands.
• Repair synthesis follows (4), further displacing the previously paired strand. Eventually, the sequence displaced is complementary to the other unpaired 3' end.
• Repair synthesis follows from the second unpaired 3' end (5).

Found it in our dictionary:

https://biology-forums.com/definitions/index.php?title=Branch_migration

A proto-oncogene is a normal gene that can become an oncogene due to mutations or increased expression. The resultant protein may be termed an oncoprotein. Proto-oncogenes code for proteins that help to regulate cell growth and differentiation. Proto-oncogenes are often involved in signal transduction and execution of mitogenic signals, usually through their protein products.

Oncogene, genetic material that carries the ability to induce cancer. An oncogene is a sequence of deoxyribonucleic acid (DNA) that has been altered or mutated from its original form, the proto-oncogene. Operating as a positive growth regulator, the proto-oncogene is involved in promoting the differentiation and proliferation of normal cells. A variety of proto-oncogenes are involved in different crucial steps of cell growth, and a change in the proto-oncogene’s sequence or in the amount of protein it produces can interfere with its normal role in cellular regulation. Uncontrolled cell growth, or neoplastic transformation, can ensue, ultimately resulting in the formation of a cancerous tumour.

A tumor suppressor gene is a protective gene that helps to inhibit the growth of cancer cells in localized parts of the body. In normal cell division, cells divide and live only for a short time before dying. Cancer cells do not behave like normal cells, and begin to multiply uncontrollably. They also become immortal unless there is some intervention implemented to kill the out of control cells. A tumor suppressor gene is one half of any cell that acts to prevent the formation of cancer.

Every cell contains chromosomes from each of the person’s parents. If one of these chromosomes is damaged, missing, or mutated, the second chromosome in each pair acts as a dominant gene and prevents the mutation from causing cancer. It is possible, howeer, for these tumor suppressor genes to eventually mutate themselves due to outside factors.

Tumor suppressor genes help halt cancerous growths because they contain proteins that stop the mutated cells from growing. If damaged cells can’t grow at a rapid pace, they can’t cause cancer. Cancer becomes a probability when the tumor suppressor gene also mutates.

Mutating of a tumor suppressor gene usually occurs due to poor choices in lifestyle or habit. When a person smokes, eat carcinogen-rich foods, or fails to provide the immune system with what it needs to function properly, mutations can occur. When this happens, both chromosomes are damaged and there is nothing standing in the way of hyperactive cell division.

Mutated cells are often inherited traits that one acquires from one or both parents. It is possible to prevent any tumor suppressor gene in the body from mutating and causing cancer. One should eat foods that promote a healthy immune system because white blood cells help to seek out and destroy mutated cells. Handling stress and exercising regularly are also immune boosters. Things to avoid include smoking, eating too much fat or red meat, and living a sedentary lifestyle.

BRCA1 is a type of tumor suppressor gene found in the breast. In women who get breast cancer, the suppressor genes are usually genetically malfunctioned from birth. This is the defect that can be passed on from generation to generation, and it greatly increases a person’s risk of cancer. The same fundamental idea is at work in every system of the body, although each tumor suppressor gene has its own name and cancer preventing protein.

Gene Conversion:
 A situation in which gametocytes of an individual that is heterozygous for a pair of alleles undergo meiosis, and the gametes produced are in a 3:1 ratio rather than the expected 2:2 ratio, implying that one allele was converted to the other.

 Sister chromatid exchange:
 Sister chromatid exchange (SCE) is the process wherein the two sister chromatids break and rejoin with one another, physically switching positions on the chromosome. Because the exchanges occur with tremendous precision with respect to the DNA sequence, and the sister chromatids are genetically identical, no information is altered during the exchange. Such exchanges are natural events during cell replication with each cell typically undergoing three to four SCEs during each replication cycle.

 Double Strand Break Recombination Model:
 The double-strand gap model of recombination was proposed to account for genetic observations in Saccharomyces cerevisiae that could not easily be explained by the Aviemore model. It incorporated observations that double-strand gaps in DNA occur during meiosis in this yeast.
 This model differs in several important respects from the Aviemore model.
 The model, originally invoked to explain genetic observations in S. cerevisiae, is consistent with many molecular observations regarding recombination in that organism. It is less consistent with observations made studying the genetics of Ascobolus immersus.
 Models are hypotheses constructed to explain observations (facts). Though they are usually a good approximation of what happens, occasionally new information will overturn a model.

 Branch Migration:
 The process in which a crossover point between two DNA duplexes slides along the duplexes. The process by which a single invading DNA strand extends its partial pairing with its complementary strand as it displaces the resident strand from a DNA duplex.