Such a cross involving two pairs of contrasting

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Unformatted text preview: d cross, Mendel also designed experiments in which he examined two characters simultaneously. Such a cross, involving two pairs of contrasting traits, is a dihybrid cross, or two-factor cross. For example, if pea plants having yellow seeds that are round are bred with those having green seeds that are wrinkled, the results shown in How Mendel’s Peas Become Wrinkled: A Molecular Explanation O nly recently, well over a hundred years after Mendel used wrinkled peas in his groundbreaking hybridization experiments, have we come to find out how the wrinkled gene makes peas wrinkled. The wild-type allele of the gene encodes a protein called starch-branching enzyme (SBEI). This enzyme catalyzes the formation of highly branched starch molecules as the seed matures. Wrinkled peas, which result from the homozygous presence of the mutant form of the gene, lack the activity of this enzyme. The production of branch points is inhibited during the synthesis of starch within the seed, which in turn leads to the accumulation of more sucrose and a higher water content while the seed develops. Osmotic pressure inside rises, causing the seed to lose w...
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This document was uploaded on 04/02/2014.

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