Genes determine the variation in plant traits. Different versions of a gene can lead to different traits. However, genes are not the only determinant of such traits, and researchers are learning more about another contributor: epigenetics. Epigenetic factors are things that regulate genes, altering their expression, and like genes, they can be inherited from generation to generation, even though they are independent of the actual DNA sequences of the genes. One epigenetic mechanism is DNA methylation, which can turn genes on or off with the addition of chemical tags called methyl groups. Genes that share the identical DNA sequence, but have different patterns of methylation are called epialleles. Several studies have shown that epialleles can cause differences in traits between plant subpopulations. Mary Gehring's team at the Whitehead Institute has described evidence that epialleles alone can lead to different heritable traits in plants. In plants, methylation states of genes change most frequently during seed development, when genes are switched on or off to progress development of the organism. During this period, a conflict of interest arises in the genome of each seed between the parts inherited from its mother and father. Mother plants produce seeds fertilized by different fathers at the same time. The mother wants to give an equal share of nutrients to each seed to have many smaller seeds. But the father's interest is only for its seed to get the most nutrients and grow larger. This conflict plays out through an epigenetic mechanism called imprinting, in which, through differential methylation between the father's and mother's copies of a gene, one parent's copy is silenced in the offspring so that only the other parent's version of the gene is expressed. Gehring and her team found that when the strain loses its paternal imprinting, the timing of seed development is affected and the plant ends up with smaller seeds. This is consistent with the theory of imprinting: When the father's genes have the advantage, the seeds are larger than when both parents' genes are equally expressed. (Source: Crop Biotech Update, International Service for Acquisition of Agri-Biotech Applications.
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