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Classical Genetics
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Mendelian Genetics
Codon Table
Mutant Genes & Genetic Material
Concepts of Genetics
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Corn Snake Genetics
Polyermase Chain Reaction

 DNA Interaction

Recombinant DNA

Fruit Flies
Genetic Disorders
Why Files


microscopeThrough microscopy we are able to view and study the unseen world of micro organisms.  We have come a long way since the ancient Greek culture.  It is evident the study of reproduction and heredity began during the writings of the Hippocratic school of medicine (500 - 400 B.C.) and philosopher and naturalist Aristotle (384 - 322 B.C.).  Although the practices of the discovers before us may seem quite primitive compared to today's knowledge of heredity, we need to keep in mind that prior to the 1800's sperm and eggs had not been observed in mammals. And for this reason, genetics is considered a relatively new science.

To better understand genetics you will need to be familiar with basic vocabulary.

Eukaryotic cell literally means "true nucleus".  The term applies to all protists, plants, animals, and fungi. Eukaryotic cells have internal membranes that separate them into regions for different functions, such as mitochondria, plastids, the Endoplasmic Reticulum, Golgi Body, etc. They also possess a cytoskeleton that helps them control their shape.
bulletThe center of heredity in a eukaryotic cell is the nucleus, whereas in a prokaryotic cell (bacteria) the genetic information is stored in an area of the cell called the nucleoid region
bulletIn eukaryotes and prokaryotes, DNA serves as the molecule that stores the genetic information.  In viruses either DNA or RNA contains the genetic information.  DNA stands for deoxyribonucleic acid and RNA stands for ribonucleic acid.  These  two types of nucleic acids found in organisms, along with carbohydrates, lipids, and proteins,  make up the four major classes of molecules found in living things. 
bulletWithin each DNA molecule are the units of heredity, called genes, which are part of the bigger picture that make up chromosomes. The genetic material of all organisms is composed of two complementary chains of nucleotides wound in a double helix.
bullet Chromosomes contain the genetic information that dictates what characteristics the daughter cells will possess.  It helps to visualize a chromosome as a continuous strand of DNA. 
bulletMeiosis (my-oh’sis) is the division of cells during sexual reproduction. Meiosis is the process in which a 2n cell undergoes two successive nuclear divisions (meiosis I and meiosis II), potentially producing four n nuclei; which leads to the formation of gametes in animals and spores in plants.
bullet Mitosis (my-toh’sis) is the division of the cell nucleus, resulting in two daughter nuclei, each with the same number of chromosomes as parent nucleus. Mitosis consists of four phases: prophase, metaphase, anaphase, and telophase.
bullet Cytokinesis (division of the cytoplasm to form two separate cells) usually overlaps the telophase stage. This process is the division of body (somatic) cells during reproduction. 
bulletChromosomes are most easily seen during mitosis (division of somatic/body cells) or meiosis (reduction, division of sex [egg & sperm] cells) through an electron microscope during interphase.

"The Father of Genetics"
Gregor Mendel


 There were many scientists who discussed the idea of a descent of species, however no one was successful in proving the hypothesis of heredity.  Gregor Johann Mendel is considered the "Father of Genetics", and through his experiments with garden pea plants came the basis for what we now call genetics.  This new science was not accepted until many years later when several scientists stumbled upon Mendel's papers and found that all his postulates of transmission genetics answered their questions of heredity.

 Gregor Mendel attempted to study heredity through his experimentation with plants and animals.  Mendel first experimented with the cross breeding of mice.  From his prior farm background, he knew that crossbreeding stock animals resulted in the presence, or lack of, various traits. He then attempted to find any common ground that existed in future generations, which was later termed F1 and F2 generations. Due to the public opinion of the time, experimenting with animals was frowned upon. After much thought and consideration, Mendel chose to use garden pea plants for his future experiments. His decision to use the garden pea worked well, as it reproduced many generations in a short time with remarkable and measurable results. He went on to record and explain that "inheritance was like beads on a string" and described that these traits repeatedly combined in mathematical ratios. Through his persistence and use of scientific methods, Mendel succeeded where others had failed in achieving scientific data regarding the inheritance of traits.

Mendel began to detect patterns of inheritance in the garden pea having to do with flower color, internodal stem length, pod color and pea shape. He noticed that when he crossed a certain red flowered plant with a white flowered plant, the offspring were all red. Mendel was puzzled by what had become of the trait for white flowers. He then crossed two of his second generation red flowered plants. The results of this cross were in a ratio of 3:1 (red:white). His conclusions were the factors of inheritance occurred in pairs, the factors become separated in reproduction and the factors for various traits can be inherited independent of any other factor. For example, the traits causing a plant to be tall or short might have no effect on whether its seeds are smooth or wrinkled. This scientific find prepared the way for future finds in the genetic field.

Mendel died in 1882 never realizing the importance of his work. Eighteen years later, in 1900, three other scientists, Hugo De Vries in Holland, Karl Correns in Germany, and Erick von Tschermak in Austria all reached conclusions similar to Mendel's discoveries. In researching past scientific literature, Mendel's papers were found and he received the credit for his life long work.  And from this point forward Gregor Mendel was honored with the title "Father of Genetics".


Mendelian Genetics

Genetics Wizard

Mendelism Overview


Mendelism Through Corn Snake Genetics

Introduction to M.G.

Mouse House

Mendel's Original Paper

Practice Problems

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Protein Synthesis


DNA- Deoxyribonucleic acid is the genetic material of all organisms. It is composed of two complementary chains of nucleotides wound in a double helix. Chromosomes contain the genetic information that dictates what characteristics the daughter cells will possess.  Visualize a chromosome as a continuous strand of DNA.  Arrayed along this DNA strand are the genes, specific regions whose sequences carry the genetic code for making specific proteins.

Adenine always pairs with thymine (double bond) and guanine always pairs with cytosine (triple bond).   RNA does not contain thymine, therefore uracil takes thymine's place.  This differnece is a good way to tell if you are working with DNA or RNA.  Cytosine, uracil and thymine are known as pyrimidines (six-member single ring),  and guanine and adenine are known as purines (nine-member double ring).

Models are Important

DNA was determined to be a right handed double helix based on x-ray crystallographic data by Maurice Wilkins and Rosalind Franklin.  This information was used by James Watson and Francis Crick to assemble the structure of deoxyribonucleic acid (DNA). The 3D model was presented by Watson and Crick in 1953 which later won them the Nobel Peace Prize for this remarkable discovery.

Looking at the diagram on the left of DNA, you will see that it is composed of repeating subunits called nucleotides.   Nucleotides are  composed of a phosphate group, a sugar, and a nitrogenous base.  Four different bases are commonly found in DNA as stated above: adenine (A), guanine (G), cytosine (C), and thymine (T).  In their common structural configurations, A and T form two hydrogen bonds while C and G form three hydrogen bonds.  Because of the specificity of base pairing, the two strands of DNA are called complementary.   This characteristic makes DNA unique and capable of transmitting genetic information.

The diagram below also shows the double and triple bonds between pyrimidines and purines.  Remember,  pyrimidines always bond with purines. In any segment of the molecule, alternating larger major grooves and smaller minor grooves will be noticeable along the DNA's axis.



Watch the full episode. See more NOVA.

An interesting DNA Question and answer

If RNA came first and DNA came second, is there an evolutionary advantage to DNA have thymine or a disadvantage to RNA having uracil?

DNA is more stable than RNA.  RNA, do to the 2' hydroxyl, is hydrolyzed under alkaline conditions.  This hydroxyl is important in RNA self-splicing reactions (group II introns). 

Thymidine is made from uracil (UTP--> TTP); this step requires glutamine and ATP, therefore energy input.  Cytosine is deaminated to uracil in a spontaneous reaction of about 10^7 cytidine residues daily; therefore, the uracil is recognized as foreign in DNA and is rapidly removed by a specific repair system.  If DNA contained uracil, recognition of these changes would not be recognized.  Unrepaired cytosines would result in mutations, since uracil pairs with adenine. 

For a more in-depth discussion, see


Elizabeth A. Cowles, Ph.D. , Associate Professor, Biology, Eastern Connecticut State University

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Codon Table (RNA)

There are 64 different kinds of codons but only 20 amino acids.

The Codon table link illustrates how the different triplets are named.
AUG encodes methionine, which initiates most polypeptide chains, referred to as the "start" codon.
All other amino acids except tryptophan, which is encoded only by UGG, are represented by two to six triplets.
The triplets UAA, UAG,  and UGA are termination signals, referred to as "stop" codons,  and do not encode any amino acids.






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Viruses & Bacteria

Some tumor viruses cause cancer in animals

Viral Group Cancer Type







Hepatitis B virus




Burkitt's lymphoma


Cervical cancer


Liver cancer


Plant Viruses

                    RNA viruses spread by


Horizontal transmission

from external  source

insects, freezing, injury


Vertical transmission

from parent

Asexual: propagation


Sexual: via infected seeds


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Genetic Engineering

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The complete set of chromosomes in the cells of an organism is its karyotype. 

All species have a characteristic number of homologous pairs of
chromosomes in their cells called the diploid (or 2n) number.  

Below are examples of various species.



Homo sapiens (human) 46


Mus musculus (house mouse) 40


Zea mays (corn or maize) 20


Drosophila melanogaster (fruit fly) 8


Xenopus laevis (South African clawed frog) 36


Caenorhabditis elegans (microscopic roundworm) 12


Equisetum arvense (field horsetail, a plant) 216


Saccharomyces cerevisiae (budding yeast) 32


Canis familiaris (domestic dog) 78


Arabidopsis thaliana (plant in the mustard family) 10


Myrmecia pilosula (an ant) 2


Parascaris equorum (parasitic roundworm) 2


Procambarus clarkii formally named Cambarus clarkii (crayfish) 192


Pacifastacus trowbridgii formally named Astacus trowdridgii  (crayfish) 372


 Human Karyotype

The karyotype of a normal human female contains 23 pairs of homologous chromosomes:
22 pairs of autosomes
1 pair of X chromosomes

The karyotype of a normal human male contains:
the same 22 pairs of autosomes  
one X chromosome
one Y chromosome




Pedigree Charts

This is how we trace inherited traits

click for source


click for more information about pedigree

"When boy III-1 (outlined in blue) died suddenly at a football game at the age of 19, his mother II-2, brother and sisters, friends and doctors were confused. An autopsy showed that the young athelete had died from familial hypertrophic cardiomyopathy (HCM), an inherited disease of the heart muscle. On doing the pedigree, the dead boys father II-1 had died of heart failure at an early age as had his aunt II-4 and paternal grandfather I-1. Testing of the family showed that the boy's siblings were unaffected but that his cousin III-5, whose mother II-4 presumably also had the condition, was positive for the gene. This cousin, although still healthy, would need careful medical monitoring of her condition. Hypertrophic cardiomyopathy is inherited as an autosomal dominant and like other autosomal dominant diseases does not skip generations and in this case affects both sexes. As this trait is dominant, we know that if a child has the the disease then at least one parent must also have the gene."  (National Genealogy Society)



Blank Pedigree Charts Generation Pedigree
  The Hunt for mtDNA

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Reginald Punnett and William Bateson were among the first English geneticists.
Punnett devised the "Punnett Square" to depict the number and variety of genetic combinations, and had a role in shaping the Hardy-Weinberg law. Punnett and Bateson co-discovered "coupling" or gene linkage. William Bateson brought Mendel's laws to the attention of English scientists.


Punnett Square

Male:  Bbrr  (Br  Br  br  br)

Female: BbRR  (BR  BR  bR  bR)



























This matrix reveals the F2 from a breeding pair of corn snakes, Pantherophis guttatus.


Hardy Weinberg Equilibrium

p2 + 2pq + q2 = 1

We will use two alleles, A and a, with the dominant allele represented by the letter p and the recessive allele by the letter q.

p = the frequency of the dominant allele (represented here by A)
q = the frequency of the recessive allele (represented here by a)

p2 = frequency of AA (homozygous dominant)
2pq = frequency of Aa (heterozygous)
q2 = frequency of aa (homozygous recessive)


Mathematical Definitions:

Allele Frequencies = p (A) + q (a) = 1

Genotypic Frequencies = (p+q)2

p2 (AA) + 2pq (2Aa) + q2 (aa) = 1


This law assumes random mating in each generation and no disruption of allele frequencies or genotypic frequencies. If the end result is not 1, there is no equilibrium.

Possible reasons for population diversity (or lack of equilibrium): genetic drift, mutation, migration, and meiotic drive.

































 c 2=




Df =


Circle one

Reject or Accept 

S = sum of

Df  = degrees of freedom

c2 = Chi Square


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