Genotyping: 只针对已知可能存在简单的变异的一些位点进行检测（不会全部检测，看价钱）。优点：便宜；
Genotyping is about the simple mutations in your DNA。There a large number of known varitations in the genomes (also known as SNP, rs, Indels, microsatellites, STS...)
Humans are diploid organisms. This means the chromosomes are in pairs (i.e there are two chromosome 1's etc.etc).
Each chromosome has one allele and both chromosomal alleles form the genotype of the individual at that spot in the genome.
When you use a technology to determine what that individual's alleles are at a given position in the genome (often done for a single nucleotide at a time) you determine the genotype, or you are genotyping.
Most of the time genotyping will look for a predetermined allele and will report that allele to be present or absent.
Genotyping is generally a cheaper and more accessible technology。 eg,利用基因芯片的Genotyping，只有特定的监测点。
Resequencing: involves a complete sequencing of the genome/segment of DNA. Of course， when you do resequencing you are trying to detect all previous variation types on the resequenced region.
When you resequence you do not look for a sparce set of predetermined alleles but you are simply sequencing the whole or parts of a samples genome to see what the whole targeted regions all alleles/genotypes are.
Variant calling: 我的理解，就是 sequence-based genotyping，但范围是所有的测序点，WGS 或者Exome
23&me 对于 genotyping 和 sequencing的介绍 https://customercare.23andme.com/hc/en-us/articles/202904600-What-is-the-difference-between-genotyping-and-sequencing-