What are single nucleotide polymorphisms (SNPs)?

The following quotes were taken from the U.S. National of Medicine Library.

"Single nucleotide polymorphisms, frequently called SNPs (pronounced “snips”), are the most common type of genetic variation among people. Each SNP represents a difference in a single DNA building block, called a nucleotide. For example, a SNP may replace the nucleotide cytosine (C) with the nucleotide thymine (T) in a certain stretch of DNA."

Since humans have about 3.5 billion nucleotides bases, how many Nucleotide Polymorphisms are there in us?

"SNPs occur normally throughout a person’s DNA. They occur once in every 300 nucleotides on average, which means there are roughly 10 million SNPs in the human genome. Most commonly, these variations are found in the DNA between genes. They can act as biological markers, helping scientists locate genes that are associated with disease. When SNPs occur within a gene or in a regulatory region near a gene, they may play a more direct role in disease by affecting the gene’s function."

What effect do Nucleotide Polymorphisms have on human health?

"Most SNPs have no effect on health or development. Some of these genetic differences, however, have proven to be very important in the study of human health. Researchers have found SNPs that may help predict an individual’s response to certain drugs, susceptibility to environmental factors such as toxins, and risk of developing particular diseases."

Can SNPs be used to keep track of disease inheritance within a family or kin ?

Yes, "SNPs can also be used to track the inheritance of disease genes within families. Future studies will work to identify SNPs associated with complex diseases such as heart disease, diabetes, and cancer.."

(U.S. National Library of Medicine, 2018)

References:

U.S. National Library of Medicine. (n.d.). What are single nucleotide polymorphisms (SNPs)? U.S. National Library of Medicine. Retrieved from https://ghr.nlm.nih.gov/primer/genomicresearch/snp