And, the region around the genome is also the same, because regions of the genome adjacent to that single mutation increased in frequency as well (they “hitchhiked”).This produces a genetic block of highly reduced diversity since the hard selective sweep increases the frequency of so many variants which are associated with the advantageous one, and may drive to extinction most other competitive variants.The key to understanding soft sweeps is that there isn’t a focus on a singular mutation.
It is taken from A recent bottleneck of Y chromosome diversity coincides with a global change in culture (Kamin et al.).Over the past few years a peculiar fact long suspected or inferred has come into sharp focus: some of the Y chromosome haplogroups very common today were not so common in the past, and their frequency changed very rapidly over a short time period. did was look at sequence data across the Y chromosome to make deeper inferences.A classical example is lactase persistence in Northern Europeans and Northwest South Asians (e.g., Punjabis).The mutation in the LCT gene is the same across a huge swath of Eurasia.In fact, soft selection often operates on standing variation, preexistent alleles which were segregating in the population at low frequencies or were totally neutral.
Genetic signatures of these events are less striking than those for hard sweeps because there is far less diminishment of diversity, since it’s not the increase in the frequency of a singular mutation and the hitchhiking of its associated flanking genomic region. But truncation selection can occur on polygenic traits, so depending on the architecture of the trait (i.e., effect size distribution across the loci) one can imagine them associated with hard selection as well.
I’ve told that you can already read The University We Need on Google Books.
I can’t vouch for this, but on Amazon the publication date is July 10th.
All individuals below (or above) a certain phenotype value have a fitness of zero, as they don’t reproduce.
In a single locus context, hard selection would involve deleterious lethal alleles, whose impact on the genotype was the same irrespective of ecological context.
So in a hard selection, it operates by reducing the fitness of individuals/genotypes to zero.