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GENOMIC IMPRINTING, One of the basic principles of Mendelian inheritance is that the origin of a, gene i.e., whether it comes from the father or the mother does not affect its, expression. This is why reciprocal crosses give identical results. We have also, studied that reciprocal crosses do not give identical results in case of, sex linked inheritance and cytoplasmic inheritance. This is because in, these examples there is a difference in the genetic material that is passed to the, progeny. Scientists noted that there are some autosomal genes that show, differences in expression depending on the parent from whom they are, inherited. This is called genomic imprinting. In other words, genomic, imprinting causes genes to be expressed in a parent-of-origin specifie, manner. Almost 300 imprinted genes are known in human beings., Genomic imprinting is a type of epigenetic (Greek, epi = over, outside of), phenomenon. Epigenetics refers to heritable changes in phenotype, without any change in the genotype of an organism i.e., features that, have an inheritance process outside the traditional genetic mechanisms. As, opposed to mutations which alter the sequence of nucleotides, epigenetic, processes alter the expression of genes and hence the phenotype. Common, mechanisms of genomic imprinting are :, 1, Preeti Mam

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SPERM, EGG, МОTHER, FATHER, NB, FEMALE, IMPRINTED GENE, MALE, IMPRINTED GENE, BABY, DOMINANT MATERNAL GENE B AND, PATERNAL GENE C ARE NOT EXPRESSED IN THE, CHILD BECAUSE OF GENOMIC IMPRINTING, a, NC, SOMATIC CELL OF, THE BABY, FIGURE 17.10 Effect of genomic imprinting on inheritance, 3, Preeti Mam