To examine G2a-L497:
According to yfull's estimates, there were only three surviving branches of L497 at 3,200 BC. However, during the first half of the third millennium BC, yfull estimates that L497 underwent a massive expansion and development, with 12 new branches forming in 2,600 BC alone (CTS4803, G727567, Z16770, Y14684, Z16775, Z726, L43, Z1823, Y8903, FGC807, Z1816 and Z6911). All of these branches look West European and are estimated to have arisen during the Bell Beaker expansion period, long before the Urnfield culture and the Celts came into existence. My own estimates, calculated using different methodology, look similar.
Also according to yfull's estimates, there were only two surviving branches of R1b-L51 at 3,200 BC. However, during the first half of the third millennium BC, yfull estimates that L51 also underwent a massive expansion and development, with scores of new branches forming in Western Europe at the same time that L497 was rapidly expanding and developing in Western Europe. My own estimates also look similar to yfull's in this respect.
The early developments of G2a-L497 and R1b-L51 are both believed to have occurred in South East Central Europe. The best fit for core R1b Bell Beaker mtDNA (across its range) includes a 50% contribution from South East Central European Cucuteni Triploye, which is believed to have been substantially an Early European Farmer G2a population. The Cucuteni Tripolye culture ended in South East Central Europe shortly after 3,500 BC; G2a-L497 and R1b-L51 in South East Central Europe ended with it. Both L497 and L51 relocated to Western Europe and underwent massive expansions contemporaneously several hundred years later, sharing female DNA in common.
It looks like Bell Beaker was a hybrid, with components mixed from these two cultures and populations. This mixing was likely to have occurred substantially where the two populations originally co-existed (i.e. in South East Central Europe), and either before or at the time that both relocated contemporaneously from South East Central Europe to Western Europe (i.e. on or before 3,500 BC).
We can see that G2a-U1's development did not follow this same pattern, but can we tell whether G2a-CTS342 followed a similar early development to G2a-L497?