During meiosis the child will have mutation in chromosome.
Step-by-step explanation:
A mutation in chromosome will lead to abnormal number of chromosomes in a child.
The condition is termed aneuploidy in which either a chromosome breaks or non-disjunction of chromosome occur in the meiotic phase.
In the pachytene phase when crossing over does not occur properly the mutation occurs in chromosome.
in the Metaphase the crossing over led the mixing of alleles this phase mutation can also occur.
In the crossing over sometimes the part of chromosome gets deleted leading to deletion of DNA sequences and hence mutated chromosome.