When passing DNA to offspring certain alleles can only become active if they were received from the mother, others only become active when they come from the father. If a gene passed is suppressed through imprinting from one parent, and the allele from the other parent is not expressed because of mutation, neither can act and the child will be defficient. A healthy child can not be produced when both sets of chromosones come from the same parent. Imprinting of the same areas will occur and all these genes will be suppressed.
A proceess known as reprogramming? occurs by the parent female or male when the egg? or sperm is maturing. This can be achieved by altering some of the DNA units by adding a methyl (CH3) group - which causes the gene not to be expressed.
Imprinting is known to cause problems in cloning, with clones having DNA which is not methylated? in the right places. Some scientists think this is due to there not being enough time for reprogramming to be properly achieved. When the nucleus is added to the egg during [somatic cell nuclear transfer]?, the egg starts dividing in minutes, as compared to the days or months it takes for reprogramming in the body. It may be possible to delay the division in clones, giving time for proper reprogramming to occur.
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