Key Questions

  • Answer:

    Genomic imprinting is an epigenetic phenomenon that causes genes to be expressed in a manner specific to their parent of origin.


    Genomic imprinting is an inheritance out of Mendelian borders. Many of inherited diseases and human development violates Mendelian Laws of inheritance. This way of inheriting is studied in epigenetics. Epigenetics shows that gene expression undergoes changes more complex than modifications in the DNA sequence. It includes the environmental influence on the gametes before conception.

    Genetic imprinting is a process of silencing genes through DNA methylation. The repressed allele is methylated, while the active allele remains unmethylated. Genomic imprinting occurs when two alleles at a locus are not functionally equivalent and is considered the primary epigenetic phenomenon that can lead to the manifestation of parent-of-origin effect. Epigenetic changes can be induced by environmental factors at different times in life.
    When epigenetic changes occur in sperm or egg cells that lead to fertilization, epigenetic changes are inherited by the offspring.

    Imprinting is a dynamic process. It must be possible to erase and re establish imprints through each generation so that genes are imprinted in an adult may still be expressed in that adult's offspring. The nature of imprinting must therefore be epigenetic rather than DNA sequence dependent. Genomic imprinting uses the cell's normal epigenetic machinery to regulate parental specific expression.

    It is now known that there are atleast 80 imprinted genes in human and mice, many of which are involved in embryonic and placental growth and development. Forms of genetic imprinting have been demonstrated in fungi, plants and animals.

  • Answer:

    Epigenetics refers to heritable changes in our gene expression that do not alter our DNA .


    This means that our phenotype , what is expressed, is altered in some way without altering our DNA due to external or environmental variables. Genes may be expressed or silenced or read differently, but the underlying DNA code remains the same.

    These epigenetic changes can happen due to DNA methylation, histone modification, and RNA-associated silencing.

    DNA methylation adds a methyl group to the DNA, which changes transcription. Histone modification works by adding either an acetyl or methyl group to lysine located in the histone. Non-coding RNAs, antisense RNA, and RNA interference may also alter expression by causing histone modification, methylation, and by causing heterochromatin to form. All of these examples mentioned in the previous sentence silence genes.

    © 2008 Nature Publishing Group Egger, G. Epigenetics in human disease and prospects for epigenetic therapy. Nature 429, 457 (2004). All rights reserved.

    Epigenetic changes may be beneficial, harmful, or completely neutral. Recent epigenetic work has suggested that trauma may be inherited , the epigenetics of a father's sperm affects his offspring's risk of autism, and mothers consuming a diet high in fiber may reduce their child's risk of asthma .

    Here's a good site from the University of Utah and Nature also has an excellent webpage on this topic.