Genetics

Genetics is an old scientific discipline that is currently exploding with new discoveries.

See here for a complete tutorial site on classical genetics, and here for a complete tutorial site on the molecular explanation of genetics.  Understanding DNA, the code-carrying molecule in the nucleus of our cells, took a great leap forward due to the detective work done by Watson, Crick, Franklin, and others.  Four bases connect two strands of DNA through hydrogen bonding in a double-helix.  Three pairs of these bases make up a codon, which determine the order of amino acids that make the proteins that make up the structural and functional parts of cells.  DNA can be copied by the cell before it divides in a process called Mitosis.  The cell cycle describes how you developed from a single cell to the billions that make you now, and how you can repair damaged tissue and replace lost skin cells for example.  When it comes to making another human through sexual reproduction, there must be a special kind of cell division called Meiosis to create gametes.  Sperm for the male and ova for the female.  These special cells have only one copy of each of the 23 different chromosomes and are called haploid.  Once combined to make a zygote with 46 chromosomes (one of each from each parent) mitosis can begin to make you into a normal (diploid) organism.  Scientists can make pictures of your chromosomes during mitosis (when your DNA is condensed and compact) to help understand genetic disorders, for example.  The image is called a karyotype.  During meiosis to make the gametes there is a great deal of genetic variability possible, which is a good thing for evolution of a species.

The inheritance of traits is the result of the random combination of sperm and egg that form an offspring.  Since you get one copy of each chromosome from each parent, you have two copies of all of the human genes.  There is much variability in the population because most genes come in a variety of forms (called alleles), and the combination of alleles you inherit (your genotype), results in your physical, physiological, and even behavioural characteristics (your phenotype).

Mendel discovered how simple traits in pea plants were inherited by studying traits that were the result of a gene that came in only two forms, one of which was completely dominant over the other (called the recessive trait/allele).   There are not many simple examples of single-gene Mendelian traits in humans, and most are unpleasant;  wet or dry earwax, and smelly pee after eating asparagus are a couple.  Some disorders like phenolketonuria are simple Mendelian inheritance examples in humans.  Other traits show more complicated inheritance such as incomplete dominance, co-dominance, and sex-linkage.  See the playlists below to learn more.

Modern advancements in genetic technology seem limitless, but many may have implications for our privacy, our environment, and our ethics.  See here for an amazing story about gene editing used to treat cancer.  See here for an example involving the use of DNA databases to catch criminals.

See here for a little genetics practice test.