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Module 12: Basic Genetics

People are made of organs, organs are made of cells, cells are composed with genetic information. Genetics are important because we can earlier detect genetic diseases when a newborn has a genetic predisposition to disease; Ex. Cystic Fibrosis is a recessive gene. Complex traits are made up of more than one gene.

We can also use genetic information to create "custom drugs" in a practice called pharmacogenetics. Genetic factors account for 20% to 40% of inter-individual differences in metabolism and response. Genetic variants can alter the pharmacodynamics of a drug, potentially increasing efficacy or toxicity.

Somatic Cell Structure of Eukaryotes

All living things are made of cells. There are two types of cells:

  • Somatic - differentiate to create organs required by an organism
  • Germ (sex)

From a genetics POV the most important part of the cell is the nucleus, where the chromosomes are stored. Humans have 23 pairs of chromosomes, each set has 1 from the mother and 1 from the father. They are ordered from largest to smallest, (1 is largest, 22 is smallest). The 23rd is the sex chromosome, which is XX is females and XY in males.

DNA

Chromosomes are made up of Deoxyribonucleic acid (DNA) molecules. DNA molecule is packaged into chromosomes in a double helix ladder structure. The "rungs" of this ladder are bases or nulceotides. The two strands of the helix are complementary.

Nucleotides:

  • Purines: Adenine and Guanine (A, G)
  • Pyrimidines: Thymine and Cytosine (T, C)

DNA Packaging

DNA molecules are packaged in a complex manner into chromosomes.

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In each cell there's nearly seven ft of DNA.

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DNA is not tightly packed into chromosomes all the time, it only condenses when the cell is getting ready to divide.

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Cytogenetic Location

Each human chromosome has a short arm ("p" for petite) and a long arm ("q" for queue), seperated by a centromere. The ends of the chromosome are called telomere. Each chromosome arm is divided into cytogenetic bands that can be seen using a microscope and special stains. At higher resolutions sub-bands are seen within bands.

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These bands are numbered p1, p2, p3... q1, q2... etc. Counting from the centromere out toward the telomeres. This is the process geneticists use to address the location of a band or a range of bands of a gene.

Ex. 7q31.2 indicates it is on chromosome 7, q arm, band 3, sub-band 1, and sub-sub-band 2. The ends of chromosomes are labeled ptel and qtel; 7qtel refers to the end of the long arm on chromosome 7.

 

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