[Pet Biology 201 : Phenotypes and hormones]

According to current scientific knowledge, the human genotype consists of two groups of phenotypes: PO and PH. The PH phenotypes are subdivided into the PH-1 phenotype and the PH-2 phenotype.

POBS, PHBS, and HYPH are special cases that will be considered in Pet Biology 102. POBS is applicable to the PO phenotype. Both PHBS and HYPH are applicable to PH-1 and PH-2.

The gender of a human is determined by the sex-chromosomes X and Y. Females are born with two X-chromosomes, males with one X chromosome and one Y chromosome. The Y-chromosome contains a gene called SRY. In most mammals the SRY gene triggers male development. In the human population this SRY gene has a double function. It triggers male development, but it also modulates the OXTR gene. SRY inhibits the expression of the OXTR PH receptor. This makes a male PH phenotype impossible.

There are five different forms of estrogen code-named E1 to E5. During each phase of life one of them becomes dominant.
Between menarche and menopause estradiol (E2) is the dominant estrogen in non-pregnant females. During pregnancy the dominant estrogen role shifts to estriol (E3). Estrone (E1) becomes dominant in postmenopausal women. Estetrol (E4) however is only produced during pregnancy.

But they all have to share their place at the top with estroxin (E5) once the phenotype expression stabilizes. Except in the case of HYPH where estroxin clearly takes the leading role. There is still some discussion in the academic world about HYPH during pregnancy.

A cell consists of the cytoplasm enclosed by a cell membrane and the cell nucleus. DNA is found in both areas. The main components of the cytoplasm are cytosol (a gel-like substance) and the organelles (the cell’s internal sub-structures). The nucleus consists of nucleoplasm enclosed by a nuclear membrane and the nucleolus. One of the organelles is the mitochondria, the mitochondrion is a semi-autonomous double-membrane-bound organelle found in most eukaryotic organisms and functions as the powerhouse of the cell.

The mitochondrion has its own independent genome (mitogenome) and DNA, This is known as the mitochondrial DNA or mtDNA. Mitochondria were one of the first GME known to science. Most of the cell’s DNA, also called nuclear DNA, is contained however in the cell nucleus. Scientists suspect that somatotropin uses mtDNA from the GMEs to complete the transformation typical to PH-2 phenotype.

Both estrogens as well as oxytocin have receptors in the human body. These receptors when activated will cause a cascade through the organism by way of activating several different messenger systems. Science knows of four types of estrogen receptors ER-alfa and ER-beta which are present in all humans, ER-gamma which is only found in fish and ER-delta which is only present in the PH-2 phenotype. Some hormones have a preference for certain receptors. Estrone (E1) only binds with the ER-alfa receptor and estriol (E3) only binds with the ER-beta receptor. Estradiol (E2) has no preference and will bind with both ER-alfa or ER-beta while estroxin (E5) will only bind with ER-delta.

ERs are found dormant in the cytosol of human cells. ER-delta are only found in PH-2 phenotype and will only bind with estroxin. Once activated by estroxin, ER-delta is able to translocate into the nucleus and bind to the DNA to regulate the activity of different genes, among them the GH1 gene which encodes for the growth hormone somatotropin. At the current state of being, ER-alfa and ER-beta can be significant for the study of human biology as a whole but for pet biology they're of minor importance.

Five types of oxytocin receptors are known to science. OXTR PO is found only in the PO phenotype and OXTR PH is found only in the PH phenotype. Independent of the phenotype each human also has one of the following oxytocin receptors: OXTR GG, OXTR AG, or OXTR AA.

Oxytocin has no preferred receptor, but the effect of binding with a receptor depends on the place of the oxytocin receptor. Oxytocin receptors in the mammary glands trigger lactations, uterus OXTR play a role during parturition and OXTR present in the central nervous system modulates a variety of behaviors. Of these the OXTR PO is found to be responsible for Pet Owner behavior and the OXTR PH is found to be responsible for Pet behavior. OXTR GG, OXTR AG and OXTR AA are thought to encode for behavior that can be expressed by members of either group. But a more in-depth study of that kind of behavior would lead us beyond the scope of this paper.

What many scientists suspected for a long time has been confirmed. That after lengthy and comprehensive research even including interspecies ones the phenotypes are linked to part of the X-chromosome that is unique to humans. This gene, codenamed phenotype encoder or PTX, serves as the blueprint for the receptors OXTR PO, OXTR PH, and ER-delta. Scientists think that the production of estroxin is also linked to this gene but more study is needed to get to the bottom of this.

Most mammals that went through puberty have their gonads fully formed and active. Humans who went through first puberty also have their gonads fully formed. However their gonads remain dormant until the estroxin level has stabilized itself. Thus PO phenotype becomes fertile after going through first puberty. So scientists expected that PH phenotypes became fertile after their second puberty but the PH phenotype stayed sterile even after second puberty when the estroxin level of PH phenotype stabilizes. Science has called this PHGD or Pethood Gonal Dormancy. See Pet Biology 301 for more details about PHGD. A speculative theory claims that this is the reason why PH phenotype has evolved into today's "petgirls".