DNA Basics For Pathway

THE BASICS

WHAT IS DNA?

Have you ever wondered why your eyes and hair are a certain color, why a friend is exceptionally tall or short, why someone has a certain health issue or disease, or maybe even why people from certain parts of the world share some of the same traits?

The answers lie in DNA…[Graphic of a crowd of people on a street, could zoom in to different looking people, then fade out to the letters DNA, or simply an animated gif that fades from a crowd picture to the letters DNA]

DNA is Deoxyribonucleic acid, a molecule containing the biological and hereditary information that makes each of us similar and unique at the same time. DNA determines brown hair, blue eyes, short, tall, as well as other inheritable traits, diseases, or likelihood for diseases. DNA is passed from parents to children, regardless of species, and is almost like a recipe for creating cells. [Show crowd picture, highlight people, hair, faces, short, tall, random people]

We all know that the basic building blocks of every living thing are cells. DNA is contained in the nucleus (nuclear DNA) and mitochondria (mitochondrial DNA) of cells. DNA molecules are tightly contained in packages called chromosomes. Your body’s complete set of DNA, also known as a genome, is divided into 23 chromosomes. [Show cell, highlight nucleus and mitochondria. Then show DNA moving within cell.]

We inherit half of our nuclear DNA from our father, and half from our mother. All mitochondrial DNA comes from our mother. Most genetic code is similar from person to person, but every one of us carries unique differences in our DNA instructions or sequencing. [Show mother and father animated characters, split out to show DNA coming from each, going to children]

What is DNA made of?

The building blocks that make up DNA are nucleotides. Nucleotides link into chains to form stands of DNA. [Animation of nucleotides coming together to form a spinning DNA strand] Nucleotides in turn are comprised of phosphate groups, sugar groups, and one of four different types of nitrogen bases.

The nitrogen bases found in nucleotides are: adenine (A), cytosine (C), guanine (G), and thymine (T). The order of these bases (A, C, G, T) [Show letters ACGT moving, coming together, changing order, etc] determines precisely which biological instructions are contained in a strand of DNA. Single letter differences in genetic codes make us different from other people, and even more likely to develop health conditions that others with different sequences may not develop.

DNA sequences of instructions are referred to as genes, the units of heredity. Genes contain instructions on how to make proteins. Proteins are complex molecules made up of amino acids. Cells structures are made up largely of proteins, and these proteins do most of the work in our cells, and our bodies as a whole. [Block diagram, showing DNA sequence break down to proteins, and amino acids]

The human genome, the entire amount of DNA sequences in a human contains about 20,000 plus genes on 23 pairs of chromosomes. [Show DNA helix with “20,000 plus genes on 23 pairs of chromosomes” text overlay]

What are Genetic Markers?

Genetic code differs from one person to another. These differences can include one different letters sequences, like a G instead of an A, or a T for a C. [Show letters ACGT moving, coming together, changing order, etc] Sequences can also an extra letter like two T's instead of one G, referred to as an insertion. Sequences can also have one letter fewer, known as a deletion.

Genetic code differences can be used as flags or markers for DNA that could affect your health. They are called single nucleotide polymorphisms, or SNPs (often pronounced "snips"). [ Show TTACGT with the TT highlighted]

Over the years of DNA research, science has identified many important genetic code sequences. Looking at a person’s genetic code, we can see whether you have the genetic sequences associated with an increased risk of a disease or condition. [Generic graphics of workers in a lab]

DNA sequencing reads the letters in your genome in the order that they appear. [Graphics of workers in Pathway lab] Taking this concept a step further, Genotyping is a means of using scientific methods to determine the genotype of an individual. We look for letter patterns that can be traced to traits.

GENETICS

Genetics is the study of how humans and animals inherit traits and features ancestors, passed down from generation to generation. [Graphic of parents and children, or grandparents and children]

The features geneticists work to identify and classify are known as traits. Your most obvious traits are physical traits like your hair color, skin color, eye color, or height and weight. Other traits can include resistance to or likelihood of disease, or behavioral traits. Traits can be inherited, or influenced by environment or lifestyle. For example, a tall mother and tall father are likely to have a tall child. A person that smokes is more likely to get lung cancer than someone who does not smoke. [Block diagram “Behavior” vs “Environment”]

Parents’ genes are divided to their offspring in pairs. Humans have two copies of each gene. When a sperm fertilizes an egg, the resulting child will have a new set of genes, contributed from each parent. Types of genes are called alleles. There are two types of alleles, dominant and recessive. Dominant alleles override weaker recessive alleles.

Genes are divided from parents to their offspring, and inherited as units. Humans have two copies of each of their genes. When an egg and a sperm join together, the union gives the child its genes, a whole new set of unique genes, from each of the parents’ genes.

WHAT ARE CHROMOSOMES

Chromosomes are organized DNA structures found in our cells, and vary widely from organism to organism. Chromosomes within cell structures vary as well. Some cells have larger linear chromosomes. These are eukarytotic cells, basically cells with a nucleus. Prokaryotic cells do not have defined nuclei and have smaller circular chromosomes. Cells can also contain more than one type of chromosome. For example, mitichondria within plants can have their own tiny chromosomes in addition to other cellular chromosomes.

Cellular division allows chromosomes to replicate, divide, and pass to daughter cells. Chromosomes can be duplicated or unduplicated. Unduplicated chromosomes have single linear strands, while duplicated chromosomes contain two copies joined together. [Illustration of cells dividing]
Your body’s complete set of DNA, also known as a genome, is divided into 23 chromosomes. The human genome, the entire amount of DNA sequences in a human, contains about 20,000 plus genes on 23 pairs of chromosomes.

WHAT ARE GENES

Genes are the basic units of heredity, and contain instructions on how to make proteins, the building blocks of cells. The human body is made up of many varieties of cells, and nearly 50 trillion cells in all. Most cells have a nucleus, which contains 99.9% of genes.

Your genes have been passed down generation-to-generation, parent-to-parent. Genes tell cells how to work, and what genetic traits to display. A gene is a portion of DNA containing "coding" sequences that determine what the gene does, and "non-coding" sequences that determine when the gene is active, also referred to as “expressed.” An active gene copies coding and non-coding sequences during a process called transcription, producing an RNA copy of the gene's information.

FROM GENES TO PROTEINS

Genes contain the information to make proteins, the essential element to cell creation. The creation of protein takes place within the cell itself. The two major components of protein creation are transcription and translation.

During transcription, gene DNA is transferred to a molecule in the nucleus of the cell called RNA, or ribonucleic acid. The RNA that contains the information for making a protein is called messenger RNA (mRNA) because it carries the information from the DNA out of the nucleus into the cytoplasm area of the cell.

Once the mRNA is in the cytoplasm, translation occurs. The mRNA interacts with a complex called a ribosome, which translates the sequence of mRNA bases. A second type of RNA called transfer RNA (tRNA) assembles the protein, which is made up of amino acids. Protein creation continues until the tRNA encounters a stop message. [Graphic or animation showing mRNA moving into cytoplasm, meeting up with tRNA]

MAKING SENSE OF SNPs

Genetic code differences can be used as flags or markers for DNA that could affect your health. These are called single nucleotide polymorphisms, or SNPs.

When cells duplicate, sometimes mistakes are made. These mistakes show as variations in DNA sequencing, or SNPs. SNPs vary the protein instructions of cells, and cause variations which can influence genetic traits related to everything from appearance to drug response, to disease propensity. [Show DNA strand or letter sequence with SNP highlighted]

Since you get your DNA from your parents, you also get their SNPs. Analyzing the number of SNPs where you match another person can indicate how closely related you are to that person. You will match many SNPs with parents and other close relatives.

Identifying and tracking genetic variations aids the development of more effective medicines and medical treatments. Scientists use two approaches in identifying SNPs: genomic and functional approaches.

Genomic approaches strive to catalog every SNP in the human genome. Using powerful computers, the genomes of hundreds of individuals are compared to identify differences. Results are cataloged and added to databases that are widely available on the Internet for research purposes. [Show graphic of scientist researching]

The functional approach is geared towards particular diseases and drug responses. The genes of people with certain diseases are compared to the genes of people without the diseases. By comparing these DNA sequences, scientists hope to isolate the SNPs corresponding with those diseases.

There are two categories of SNPs: linked and causative.

Linked SNPs are not housed within genes and have no affect on protein function. They correspond to drug responses or to risks for certain diseases.

Causative SNPs do affect protein function, and correlate with a disease a person's response to medication. There are two types Causative SNPs. Coding SNPs within the coding region of a gene change amino acid sequences of gene protein. Non-coding SNPs housed with a gene's regulatory sequences change gene expression and how much RNA and protein is produced.

GENOTYPING VS. SEQUENCING

DNA sequencing reads the string of nucleotide bases—adenine, guanine, cytosine, and thymine, or the A's, T's, G's and C's in your genome in the order that they appear. Determining the sequence of bases tells us the kind of genetic information that is carried in a particular segment of DNA. DNA sequencing advances since the 1970's have given science a blueprint of how humans are constructed. [Show A's, T's, G's and C's, or animate]

The genetic sequence of DNA contains the A's, T's, G's and C's. Most of the sequence is the same from individual to individual, but there are instances where single letters in the sequence differ in individuals. These singles letter differences are known as SNPs, or single nucleotide polymorphisms.

SNPs form the basis for genotyping. Genotyping is a means of using scientific methods to determine the genotype of an individual. We look for letter patterns that can be traced to traits.

GENETICS AND YOU  

We use genetic code differences as markers for DNA that could affect your health. Identifying and tracking genetic variations (SNPs) aids the development of more effective medicines and medical treatments. [Show Pathway research imagery]

Genetic and environmental factors contribute to determine risk for disease. If a disease runs in your family, you are more likely to have the disease than someone who does not have that same history of disease in their family. The likelihood of disease does not mean you will get the disease, it just means you are at risk for the disease. You can learn how to protect yourself.

Illnesses or diseases caused by abnormalities in genes or chromosomes are referred to as genetic disorders. Genetic disorders can be dominant, recessive, or complex. [Show Pathway research imagery]

A recessive genetic disorder appears only in patients who have received two copies of a mutant gene, one from each parent.

A dominant genetic disorder almost always results in a specific physical characteristic, for example, a disease, even though the patient's genome possesses only one copy.

Complex genetic disorders involve more than one gene, and the genes interact with each other and/or with one or more aspects of the outside world - for example a virus or some component of diet - to produce disease.