Monday, February 15, 2016

DNA


Here are some notes about DNA, taken from a series of introductory videos produced by 23andMe and the Khan Academy.
  • The human body is made up of about 50 trillion cells. Almost every cell contains a nucleus which holds 99.9% of our genes (cell mitochondria store a few more genes).
  • The coiled DNA in a nucleus is about 6 foot long.
  • All told, we have around 20,000 genes. Together, these form our DNA.
  • DNA comprises sugar, phosphate and four bases (adenine, thymine, cytosine and guanine).
  • The bases spell out the genetic code. The numbering and ordering determines the organism and its characteristics.
  • Most genes are recipes for making specific proteins. They tell a cell how to function (e.g. whether to become a hair follicle, a brain cell or a heart cell). 
  • Gene regulators turn different genes on and off to control cell functions. 
  • The long pieces of DNA containing your genes are organised into pieces called chromosomes. Humans have two sets of 23 chromosomes. 
  • The entire set of chromosomes is call the genome. The genome comprises around 3 billion base pairs. It would take a person over 9 years to read these out without stopping.
  • When a new cell is made, a single base pair may get added, substituted or left out. These variations (single-nucleotide polymorphisms, or SNPS, also knowns as 'snips') are what us make us different from one another. 
  • Most variations produce unobservable differences, but some lead to observable changes in traits (e.g. curly hair) or to the development of various conditions. As these differences are passed on to future generations, looking at differences and similarities in genomes can tell you how closely two people are related.
  • You can get your whole genome sequenced for around $1,000. 23andMe conducts genotyping analysis, looking at around 600,000 variations of base pairs (these are called SNPs or 'snips', the locations where variations are known to occur). 23andMe focuses on those snips, which have well studied contributions to particular traits.
  • We share 99.5% of our DNA with other humans.
  • Ancestry analysis is easier using the Y chromosome for the male line (passed down from father to son) or mitochondrial DNA from the female line, as both of these sets of DNA are more likely to have stayed intact across many generations.This analysis assigns a haplogroup to the maternal and paternal lineage, relating to a particular point and place in history when a specific mutation arose and has been passed along in future generations.
  • Phenotypes = observable traits (e.g. weight, height, etc) that result from the interaction between you and your environment. Some traits are more determined by the environment than others.

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