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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.
- Fall '14