Examples of crossing over in the following topics:
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- Crossing-over (homologous recombination) is one such mechanism by which DNA variations can occur, and genes can be rearranged.
- Crossing-over is an event that occurs during meiosis when chromatids are in contact with each other and may exchange segments.
- Crossing over occurs during meiosis I, and is the process where homologous chromosomes pair up with each other and exchange different segments of their genetic material to form recombinant chromosomes.
- Crossing over is essential for the normal segregation of chromosomes during meiosis.
- Crossing over also accounts for genetic variation, because, due to the swapping of genetic material during crossing over, the chromatids held together by the centromere are no longer identical.
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- crossing over (or recombination) between chromatids of homologous chromosomes during meiosis
- However, existing genes can be arranged in new ways from chromosomal crossing over and recombination in sexual reproduction.
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- When synapsed, homologous chromosomes undergo reciprocal physical exchanges of DNA at their arms in a process called homologous recombination, or more simply, "crossing over."
- Operating under these assumptions, Sturtevant hypothesized alleles that were far apart on a chromosome were more likely to dissociate during meiosis simply because there was a larger region over which recombination could occur.
- Perfectly unlinked genes correspond to the frequencies predicted by Mendel to assort independently in a dihybrid cross.
- In (b), two genes are very close together on the same chromosome so that no crossing over occurs between them.
- In (c), two genes are far apart on the chromosome such that crossing over occurs during every meiotic event.
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- Cross reactivity occurs when an antibody binds not to the antigen that elicited its synthesis and secretion, but to a different antigen.
- Because an epitope corresponds to such a small region (the surface area of about four to six amino acids), it is possible for different macromolecules to exhibit the same molecular identities and orientations over short regions.
- For instance, antibody cross reactivity may occur against the similar surface structures of various Gram-negative bacteria.
- These antibodies may have been initially raised against the nucleic acid of microorganisms, but later cross-reacted with self-antigens.
- (b) An antibody may cross-react with different epitopes.
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- Over 90% of plants use C3 carbon fixation, compared to 3% that use C4 carbon fixation; however, the evolution of C4 in over 60 plant lineages makes it a striking example of convergent evolution.
- Cross section of a C4 plant, specifically of a maize leaf.
- Cross section of a CAM (crassulacean acid metabolism) plant, specifically of an agave leaf.
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- The garden pea also grows to maturity within one season; several generations could be evaluated over a relatively short time.
- For this reason, garden pea plants can either self-pollinate or cross-pollinate with other pea plants.
- A gardener or researcher, such as Mendel, can cross-pollinate these same plants by manually applying sperm from one plant to the pistil (containing the ova) of another plant.
- When Mendel cross-pollinated a true-breeding plant that only produced yellow peas with a true-breeding plant that only produced green peas, he found that the first generation of offspring is always all yellow peas.
- In this and all the other pea plant traits Mendel followed, one form of the trait was "dominant" over another so it masked the presence of the other "recessive" form in the first generation after cross-breeding two homozygous plants..
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- The allele for red flowers is incompletely dominant over the allele for white flowers.
- However, the results of a heterozygote self-cross can still be predicted, just as with Mendelian dominant and recessive crosses.
- However, the 1:2:1 genotypic ratio characteristic of a Mendelian monohybrid cross still applies.
- In this case, the wild-type allele is dominant over all the others, chinchilla is incompletely dominant over Himalayan and albino, and Himalayan is dominant over albino.
- Alternatively, one mutant allele can be dominant over all other phenotypes, including the wild type.
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- Mendel performed seven monohybrid crosses involving contrasting traits for each characteristic.
- Recall that Mendel's pea-plant characteristics behaved in the same way in reciprocal crosses.
- Called the test cross , this technique is still used by plant and animal breeders.
- In a test cross, the dominant-expressing organism is crossed with an organism that is homozygous recessive for the same characteristic.
- This cross produces F1 heterozygotes with a yellow phenotype.
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- Mendel's crosses involved mating two true-breeding organisms that had different traits to produce new generations of pea plants.
- Mendel performed crosses, which involved mating two true-breeding individuals that have different traits .
- Plants used in first-generation crosses were called P0, or parental generation one, plants.
- Mendel collected the seeds belonging to the P0 plants that resulted from each cross and grew them the following season.
- In one of his experiments on inheritance patterns, Mendel crossed plants that were true-breeding for violet flower color with plants true-breeding for white flower color (the P generation).
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- Muscle tension is influenced by the number of cross-bridges that can be formed.
- In individual muscle fibers, the amount of tension produced depends primarily on the amount of cross-bridges formed, which is influenced by the cross-sectional area of the muscle fiber and the frequency of neural stimulation.
- The number of cross-bridges formed between actin and myosin determine the amount of tension that a muscle fiber can produce.
- Cross-bridges can only form where thick and thin filaments overlap, allowing myosin to bind to actin.
- If more cross-bridges are formed, more myosin will pull on actin and more tension will be produced.