Nuclear DNA v mtDNA: Principles of inheritance Medical Research Council Mitochondrial Biology Unit, University of Cambridge, Wellcome Trust/MRC Building, Cambridge Biomedical Campus, Hills Road, Cambridge CB2 0XY Nuclear DNA - Found in the nucleus of the cell - 3,300,000,000 bases arranged in linear chromosomes - Two copies of each chromosome present - Maternally and paternally inherited - Contains approximately 20,000 - 30,000 genes - 93% of the genome contains non-coding DNA Mitochondrial DNA (mtDNA) - Found in the mitochondrial matrix - 16, 569 bases in a circular chain of DNA - Multiple copies present in each mitochondrion - Maternally inherited - Contains 37 genes that encode - 13 proteins - 22 tRNAs and 2 rRNAs - 3% of the genome contains non-coding DNA ‘Mother’ cell containing mutant mtDNA Non-Mendelian inheritance Primary oocytes = Cell nucleus mtDNA amplification = Normal mitochondria Mature oocytes = Mutant mitochondria Fertilisation Low level of Mutation: Healthy child High level of Intermediate level Mutation: Severe disease of mutation: Mild disease Mendelian inheritance - This example represents an autosomal recessive disease Mother: Father: - Both parents have one ‘healthy’ gene, and one ‘disease’ ‘unaffected’ carrier ‘unaffected’ carrier gene; as the ‘healthy’ gene over-rides the ‘disease’ gene, the parents are healthy - There is a ¼ chance that their children will carry two copies of the ‘healthy’ gene, a ½ chance their children will carry one copy of the ‘healthy’ gene, and one copy of the ‘disease’ gene, and will be healthy like the parents, and ¼ chance they will inherit two copies of the ‘disease’ gene. In this case, the child will inherit the disease www.mrc-mbu.cam.ac.uk .