More on the association between low sperm motility or reduced sperm count with some y-haplogroups :
Y chromosome haplogroups may confer susceptibility to partial AZFc deletions and deletion effect on spermatogenesis impairment
Yang et al. said:
The findings indicate that some monophyletic Y chromosomes may be associated with predisposition to specific subtypes of partial AZFc deletion and adverse effect on spermatogenesis. Although these deletions were not confirmed with gene dosage analysis, the results suggest that Y chromosome background is an important factor that affects partial AZFc deletion formation and its contribution to spermatogenic failure.
AZF deletions and Y chromosomal haplogroups: history and update based on sequence
Evidence for the association of Y-chromosome haplogroups with susceptibility to spermatogenic failure in a Chinese Han population
Yang et al. said:
This study provides evidence for the association of Y-chromosome background with impaired spermatogenesis, suggesting that Y variations play a role in the occurrence and even the severity of spermatogenic failure.
The haplogroup implicated in impaired spermatogenesis in the Chinese population is O3*.
The association of Y chromosome haplogroups with spermatogenic failure in the Han Chinese
Lu et al. said:
The results indicated that the prevalences of hg K* in the control and the case population were 0.78% (4/515) and 2.80% (8/285), respectively. The difference between the frequencies of the hg K* in the infertile males and the normal control population was significant [odds ratio (OR) = 3.69; 95% confidence interval (CI) = 1.10–12.36] (P = 0.028). However, in the other haplogroups no significant differences were found. In conclusion, Y haplogroup-K* might bear a risk factor of male infertility, and the individuals in the haplogroup need to be further examined.
K is the ancestor of 90% of Y-DNA lineages in the world. But K* has virtually disappeared, except if some isolated parts of Asia, including western China. New mutations arose that obviously conferred an advantage over K*, so that only the men with the new mutations passed on their Y-DNA.
Spermatogenic ability is different among males in different Y chromosome lineage
Kuroki et al. said:
The results show that the mean sperm concentration correlates with Y chromosome type. Moreover, the occurrence of azoospermia is related to one particular Y chromosome lineage. Thus, males with a certain haplotype are at a disadvantage for fathering children. The difference of spermatogenic ability among men is important not only in pursuing male competition as in the past but also as relates to the future of modern human males.
The haplogroup in question is D. This is not surprising as it was the first with C to reach Asia, but now survives only in isolated regions like Japan, Tibet, Yunnan, some Indonesian islands or the Andamans.
Identification of a Y chromosome haplogroup associated with reduced sperm counts
Krausz et al. said:
We found that one class of Y chromosome, referred to as haplogroup 26+, was significantly overrepresented (27.9%; P < 0.001) in the group of men with either idiopathic oligozoospermia (defined as <20 x 106 sperm/ml) or azoospermia compared to the control Danish male population (4.6%). This study defines, for the first time, a class of Y chromosome that is at risk for infertility in a European population
The haplogroup numbers were taken from the Europe-wide study of
Rosser et al. (2000). Based on the geographic distribution and the STR markers given, hg26 correspond to haplogroup
Q.
The haplogroup with the highest sperm count in the study was hg1, which unsurprisingly is
R1b, followed by hg3 (R1a) . This supports my hypothesis that R1a and R1b became dominant in Europe, in spite of their late Bronze-age arrival, thanks to a genetic predisposition to father more boys compared to other haplogroups. Indeed, a higher sperm count is one of the principal factors in raising the chances of having a boy rather than a girl.
The fourth haplogroup in the study, hg2+, represents haplogroup I. The difference in sperm count between I and Q is not huge (41.4 against 30.8 mill/ml) in comparison to R1b (75.8 mill/ml).
Krausz et al. explain that :
Most of the hg26+ men have very low sperm counts. Sperm counts within this range are associated with very poor reproductive success and, in the absence of assisted reproduction, these chromosomes will be rapidly eliminated from the population. Taking into account the hg26+ frequency in the Danish population (∼5%) and assuming a mean selective disadvantage for these chromosomes of 0.5, this Y chromosome lineage would disappear from the Danish population within 12 generations.
With such a fast replacement rate, it could even be imagined that R1b arrived later than 2500 BCE in Western Europe, in fairly small number, and still would have become dominant without any massacre of indigenous men nor polygamy required.
Considering that other studies have found that haplogroup E also had a low sperm count by European standard (but probably higher than most subclades of hg A and B), it is easy to imagine how R1b (V88) could have boomed in some parts of Africa. Once the haplogroup penetrated a tribe, the proportion of R1b to haplogroup A, B or E would rise very quickly, explaining how it could reach over 95% in some tribes of North Cameroon.
