  The majority of the inhomogeneities in the chemical composition of Globular
Cluster (GC) stars appear due to primordial enrichment by hot-CNO cycled
material processed in stars belonging to a first stellar generation. Either
massive AGB envelopes subject to hot bottom burning, or the envelopes of
massive fastly rotating stars could be the progenitors. In both cases, the
stars showing chemical anomalies must have also enhanced helium abundance, and
we have proposed that this higher helium could be at the basis of the many
different morphologies of GC horizontal branches (HB) for similar ages and
metallicities. The helium variations have been beautifully confirmed by the
splitting of the main sequence in the clusters omega Cen and NGC 2808, but this
effect can show up only for somewhat extreme helium abundances. Therefore it is
important to go on using the HB morphology to infer the number ratio of the
first to the second generation in as many clusters as possible. We exemplify
how it is possible to infer the presence of a He-rich stellar component in
different clusters thanks to different HB features (gaps, RR Lyr periods and
period distribution, ratio of blue to red stars, blue tails). In many clusters
at least 50% of the stars belong to the second stellar generation, and in some
cases we suspect that the stars might all belong to the second generation. We
shortly examine the problem of the initial mass function required to achieve
the observed number ratios and conclude that: 1) the initial cluster must have
been much more massive than today's cluster, and 2) formation of the second
stellar generation mainly in the central regions of the cluster may help in
obtaining the desired values.
