Marsupial sex chromosomes break the rule that recombination during first meiotic prophase is necessary to ensure reductional segregation during first meiotic division. It is widely accepted that in marsupials X and Y chromosomes do not share homologous regions. and during male first meiotic prophase the synaptonemal complex is absent between them. Although these sex chromosomes do not... https://www.petsafewirelessfence.com/product-category/foam-bowls/