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Genetics is the study of DNA, chromosomes, and genes - and how those genes are expressed as traits (characteristics).

DNA (Deoxyribonucleic Acid) is the blueprint for life.  It is a long, thin strand that contains four "bases": adenine (A), thymine (T), cytosine (C), and guanine (G).  These four bases are used to create codes for everything that happens inside of your body - every structure and every chemical reaction.

Chromosomes are long, coiled up strands of DNA.  Different species have different numbers of chromosomes - humans have 46.  Our 46 chromosomes are really two sets of 23 - one set we get from our mothers, the other from our fathers.  So, we usually say that humans have 23 pairs of chromosomes.

A gene is a segment of DNA (in a chromosome) that codes for a certain trait/characteristic.  There are genes for hair color, eye color, handedness, height, build, even musical ability.  Most genes come in different "flavors".  For example, different versions of the eye color gene can code for brown, blue, or green eyes.  These different forms of the same gene are called alleles.

Some alleles are dominant, and some are recessive.  This means that if you happen to have one dominant allele and one recessive allele, the recessive trait will be masked (hidden) by the dominant trait.  Check out this example:

In pea plants, there are two versions of the height gene: tall and short.  The tall gene (T) is dominant over the short (t) gene.  Since pea plants have two copies of each gene (just like humans), they may have any of these three combinations of alleles:
     TT - The plant will be tall.
     T t - The plant will be tall.
(The "short" trait is hidden by the "tall.")
      t t - The plant will be short.

Homozygous means that both alleles are the same.  In the above example, TT is homozygous dominant and tt is homozygous recessive.  Heterozygous means that the alleles are different.  In this case, Tt is heterozygous.  These codes are the plant's genotype (the genes that are present).  The phenotype is the physical characteristic that shows up (tall or short).

Genetic Engineering & Genomics
Your genome is your entire set of genes.  The study of genomes is called genomics.  

Genetics Resources Online

  • Blood Typing Using Eldoncard  (3:18) - There are four spots on the card: Anti-A (reacts if the A-tag is present), Anti-B (reacts if the B-tag is present), Anti-D (reacts if the Rh tag is present), and control (does not react - for comparison).

Supporting files for this material can be found here.
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