When a cell is in G2 phase, it has already doubled in S phase its DNA, meaning that for each chromosome we have two chromatids -> 2n(number of chromosomes)×2(number of chromatids per chromosome)=number of chromatids.
If 160 is the number of chromatids on G2 phase of a chicken cell, it means that the cell has 80 chromosomes (2n), and after meiosis, process to form a sperm cell, will only have 40 chromosomes (n).
