Crossing over occurs at the four-strand stage when two homologous chromosomes, each consisting of a pair of sister chromatids, are paired. Each crossover involves just two of the four strands and generates two recombinant strands.
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Answer:
Mitosis occurs in somatic cells; this means that it takes place in all types of cells that are not involved in the production of gametes. Prior to each mitotic division, a copy of every chromosome is created; thus, following division, a complete set of chromosomes is found in the nucleus of each new cell. Indeed, apart from random mutations, each successive duplicate cell will have the same genetic composition as its parent, due to the inheritance of the same chromosome set and similar biological environment. This works well for replacing damaged tissue or for growth and expansion from an embryonic state. Because the genes contained in the duplicate chromosomes are transferred to each successive cellular generation, all mitotic progeny are genetically similar. However, there are exceptions. For example, there are genetic variations that arise in clonal species, such as bacteria, due to spontaneous mutations during mitotic division. Furthermore, chromosomes are sometimes replicated multiple times without any accompanying cell division. This occurs in the cells of Drosophila larvae salivary glands, for example, where there is a high metabolic demand. The chromosomes there are called polytene chromosomes, and they are extremely large compared to chromosomes in other Drosophila cells. These chromosomes replicate by undergoing the initial phases of mitosis without any cytokinesis (Figure 2). Therefore, the same cell contains thick arrangements of duplicate chromosomes side by side, which look like strands of very thick rope. Scientists believe that these chromosomes are hyper-replicated to allow for the rapid and copious production of certain proteins that help larval growth and metamorphosis
Explanation:
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Answer:
Thalidomide may be defined as a type of the sedative drug that in the earlier time referred for the pregnant ladies. This drug causes the world wide tragedy and acts as a teratogen.
This drug causes mutation in the fetus. The Ames test is effective to understand the mutagenicity of the drug. In this test, if the auxotrophic strain of the bacteria is grown on the the deficient media containing thalidomide drug. The bacteria growth indicates the positive Ames test and the substance is considered as mutagen.
Consuming excessive amounts of pure water creates hypotonic environment in the body fluid surrounding the cell.
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What is a hypotonic solution?</h3>
- A solution having lower osmotic pressure than the solution to which it is compared.
- It has lower amount of solute (high amount of solvent) compared to other solution separated by a semi-permeable membrane.
- After consuming excessive amounts of pure water, the body fluid becomes hypotonic, so water enters from body fluid to the cell resulting in the cell to swell or break.
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