To protect vulnerable 16 and 17 year olds, the offences of 'abuse of a position of trust' prohibits sexual contact between adults and children under 18 in schools, colleges and residential care.
Chromosome abnormalities usually happen as a result of an error in cell division. Meiosis is the name used to describe the cell division that the egg and sperm undergo when they are developing. Normally, meiosis causes a halving of chromosome material, so that each parent gives 23 chromosomes to a pregnancy.
If they break at slightly different loci, the result can be a duplication of genes on one chromosome and a deletion of these on the other. This is known as an unequal crossover. If chromosomes break on both sides of the same centromere and rejoin to exclude the centromere, the result can be one chromosome being lost during cell division.