Andorian / Human
Thanleros and Andromeda are the first of a new, hybridised species resulting from second generation genetic alterations in an attempt to reverse the reproductive and fertility crisis forcing the Andorian people toward extinction (KS19: Boy Who Cried Wolf).
Externally the Andorian/Human hybrids appear to favour their Andorian heritage however their darker hair and skin pigment is an indication that both cobalt and iron are present in their bloodstream.
The musculature and limited exoskeleton common in the Andorian species are somewhat diminished, causing a reduction in their physical strength to somewhere closer to that of an average Human. Both the redundant circulatory system, which grants Andorians their resilience to extreme temperatures, and the antennae sensory organs remain unchanged.
As a result of generations of fertility issues and their complex, four person reproductive method, the Andorian species had been on a slow decline towards extinction for a century or more. Despite the attempts by the Parliament Andoria to keep this state secret from becoming public knowledge and causing a panic amongst the populace, they have endorsed a series of research projects into solving the problem over the past few decades.
One such project was being performed in the late 2350's on the Athlirith Orbital Research Station. Using the pretence of medical treatment as a cover, a team of scientists selected a number of Andorian infants who then underwent extensive gene therapy to manipulate their reproductive systems and make them more receptive to the genetic material of alien species.
Since then a number of other attempts to alter or change the structure of Andorian DNA have been attempted. The closest anyone had came to succeeding in relieving the issue was in 2381 with the discovery of a Turn Key within the genetic structure of a species from the Gamma Quadrant known as the Yrythny. However most of the offspring produced with this method suffered from genetic problems and stillbirth so once again a solution to the crisis remained elusive.
That is until 2387 when Nilari Shendehor, one of the Athlirith Station test subjects, learned that she and her Human partner, Maxwell "Bruiser" Roessler were pregnant. Given the numerous differences in both species it was only thanks to the assistance of Nilari's brother Galian, who had been researching their parent's work on Athlirith, that two embryos were able to remain viable. Rather than a zhen though, a Human was required to carry the pregnancy to term (KS14.1: A Tiny Oversight).
Some within the Parliament Andoria refuse to believe their species is facing extinction and find endeavours to 'dilute' their strong heritage through genetic engineering an affront to Uzaveh. There are also those, such as the Treishya Party, who would prefer any and all cures were brought to the people by one of their representatives, allowing a positive spin to be put on the successful reversal of the generational crisis. As a result the existence of successful births poses a threat to many powerful people who would stop at nothing to insure the crisis remain a closely guarded secret.
Following a comprehensive report submitted by Nilari Shendehor and Maxwell Roessler through the Expanse Oversight Advisory (which included affidavits from the medical professionals involved in both prenatal and postnatal care, as well as genetics experts from the Phlox Research Institute on Denobula), the Bureau of Interplanetary Affairs stepped in to advocate on behalf of Thanleros and Andromeda Roessler. This resulted in the Federation Council ruling in their favour, granting them both citizenship and immunity from potential charges in the future (KS22: Lewis' Bond).