Two family members are diagnosed with the same genetic disorder but have distinctly different ...

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Explanation:
1. The expression of a few genetic conditions varies depending on whether the altered gene is inherited from the mother or the father. This differential gene expression is due to genomic imprinting. Imprinting takes place before gametes are formed, when certain genes are chemically marked as having maternal or paternal origin. After conception, the imprint controls gene expression so that only one allele, either maternal or paternal, is expressed. If the unsilenced (active) allele carries a mutation, disease may result and the diseases may be different.
2. Penetrance is the probability that a gene will be expressed phenotypically.
3. A new mutation is when there is no previous family history of a condition.
4. The term expressivity is used to describe the degree to which a phenotype is expressed. When people with the same genetic makeup (genotype) exhibit signs or symptoms with varying degrees of severity, the phenotype is described as showing variable expression.