Figure 2. Bottle neck representation. The first bottle neck occurs in oocyte maturation, starting in primordial cells with 10 to 200 copies of mtDNA that replicate at random, to the mature oocyte with 100,000 to 600,000 copies. The second bottle neck occurs after oocyte fertilization by the spermatozoid, the zygote formed has 100,000 to 600,000 copies of mtDNA which are randomly reduced to the formation of primordial cells with 10 to 200 copies (Adapted from Craven et al., 2017).