Has there been any explanation so far (as of episode 4) on whether or not males can be born a norma? Everyone on the norma base seem to be female.
Yes. Norma can only be female.
The survivors of the pre-mana world, like Tusk and his parents also cannot use mana (because the mana-wielders were genetically engineered by Embyro), and Tusk were incorrectly identified as a Male Norma by Hilde.
This gene rejects DRAGON-based powers. Thus norma are immune to mana, and to the dragon's roars (this being the main reason they pilot the para-mails).
If we play a little with genetics, we can say that the norma gene is a recessive gene situated in the homologous portion of the sexual chromosomes:
Homologous portion is that in which there are genes having alleles in both Y and X sex chromosomes. The homologous portions are situated more in the central part of the sex chromosomes, near the centromere.
The recessive allele appears only on the X chromosome, with the dominant allele appearing on both X and Y. The recessive characteristic grants immunity to DRAGON based powers.
Since there is little recombination between X and Y chomosomes during meiosis (and this recombination takes place only near the telomeres), there is no way this gene can cross over to the Y chromosomes.
The human Y chromosome is normally unable to recombine with the X chromosome, except for small pieces of pseudoautosomal regions at the telomeres
So only females could be norma. Males would be carriers only at most.
Now, this is viewed as a genetic flaw by the mana society (including several characters) but I boldfaced the immunity text above for a reason:
- Embyro designed the mana-wielding humanity. It would be very unlikely he would let "an old gene" slip by a mistake.
The mana society needs Aura as its Draconium reactor. It means the dragons came into existance before Embyro designed them. Since Embyro knew the dragons would go to any length to rescue Aura (even going on suicide missions), he would need troops immune to the dragon powers.
So he engineered the Norma. They were not an "accident" or a "mistake".
Why engineer his soldiers as female only? Because Embyro is a womanizer at the very core. He has no interest in males.
Also, he views the mana wielders as mere puppets. Since it is shown that he at several times seduced and enthralled the norma to satisfy his urges, he would expect some thrill out of breaking them.
He can dominate any mana wielder at will, so we can infer from his personality that he would have no interest in having a woman he can control with a flick of his finger.
So it was Embyro that designed the norma to be his anti-DRAGON soldiers, female only. So he would have some girls to toy with.