Difference in expression of gene in the sibling as inherited by the father is termed as:

Difference in expression of gene in the sibling as inherited by the father is termed as mosaicism. It results from a mutation that occurs during embryonic, fetal, or extrauterine development. When mutation occur during from nondisjunction at an early embryonic mitotic division chromosomal mosaicism occurs. Somatic mosaicism is characterized by a patchy distribution of genetically altered somatic cells. Anticipation refers to an unusual pattern of inheritance in which symptoms manifest at earlier ages and with increasing severity as traits are passed to subsequent generations. Ref: Kopp P., Jameson J.L. (2012). Chapter 61. Principles of Human Genetics. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e. Tsaic A.C., Manchester D.K., Elias E.R. (2012). Chapter 37. Genetics & Dysmorphology. In W.W. Hay, Jr., M.J. Levin, R.R. Deterding, J.J. Ross, J.M. Sondheimer (Eds), CURRENT Diagnosis & Treatment: Pediatrics, 21e.