recessive - requires a copy of the gene from both parents to exhibit the trait, Having only one copy of the gene makes the dog a carrier of the trait, and he will never exhibit the trait ? unless the gene is located on the ?X? or sex chromosome, sarcoma ? tumor formed of connective tissue cells: bone cartilage, muscle, blood vessel, or lymphoid tissue. Infection of the uterus. Pyometra is infection of the uterus that occurs during diestrus, 3-6 weeks after ovulation. It is commonly seen in bitches older than 5 years. Pyometra is also referred to as cystic endometrial hyperplasia (CEH) which is the term descriptive of the morphological changes occurring in the uterus. Hormones, primarily progesterone which is secreted from the corpus lutei (CLs) of the ovaries during diestrus stimulate CEH. The accumulation of pus inside the uterus.