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What smaller elements make up the complex DNA molecule, how are these elements arranged, and how is information extracted from them? This unit answers each of these questions, and it also provides a basic overview of how DNA was discovered.
In this unit, you will learn about the basic structure and biological function of DNA molecules, including the biochemical processes that extract the information encoded within DNA.
DNA Is a Structure That Encodes Biological Information
Traits as diverse as the color of a person's eyes and the scent of a rose are determined by the information contained in DNA. Learn how this information is coded by strings of molecules called nucleotides.
Discovery of the Function of DNA Resulted from the Work of Multiple Scientists
Although the idea of genes had been around for many years, it was not until the 1950s that the chemical nature and structure of DNA and its function as hereditary material were identified. This page is an overview of the major experiments that led to this knowledge.
Cells Can Replicate Their DNA Precisely
Each strand of DNA can act as a template for the creation of exact copies of itself, resulting in the persistence of genetic information across millions of generations. Learn how this process of replication works.
The Information in DNA Is Decoded by Transcription
During the process of transcription, DNA is converted to RNA, a complex molecule that is able to carry genetic information outside of the cell's nucleus. This page guides you through the biochemical steps of this process.
The Information in DNA Determines Cellular Function via Translation
How does DNA determine an organism’s characteristics? A process called translation decodes RNA created during transcription, and uses it to create proteins that perform specific cellular functions. This page explains the complex steps that change the information from RNA into protein.
The passage of DNA from one cell to another is the basic means by which genetic information — and therefore biological characteristics — can persist relatively unchanged across millions of generations of organisms. The mechanism by which DNA is passed from one generation of cells to the next is a combination of DNA replication and cell division. In this unit, you will learn how DNA is first packaged and then passed on to the next generation during cell division. You will also explore the unpredictable ways in which DNA can change during this process.
Introduction: How Does DNA Move from Cell to Cell?
In this unit, you will learn what happens to DNA during both mitosis, the process of cell division that happens in most cells, and meiosis, the process of cell division that happens in cells that are specifically intended to play a role in sexual reproduction. You will also discover how DNA strands can be randomly altered during either process.
Replication and Distribution of DNA during Mitosis
Cell division, the basic means by which genetic information is passed from generation to generation, involves tightly coordinated movements of a cell's DNA. This page describes the major phases of mitosis, the most common form of cell division.
Replication and Distribution of DNA during Meiosis
Cell division, the basic means by which genetic information is passed from generation to generation, involves tightly coordinated movements of a cell's DNA. This page describes the major phases of meiosis, a version of cell division that occurs in cells intended to play a role in sexual reproduction.
DNA Is Constantly Changing through the Process of Recombination
Pieces of DNA molecules are constantly being broken apart and exchanged with other DNA molecules. This process is called recombination. In this page, you will learn how recombination introduces unpredictable transformations in the information encoded in a cell's DNA.
DNA Is Constantly Changing through the Process of Mutation
Just like the mechanical components in cars or computers, the molecules inside a cell can sometimes malfunction. When this happens during DNA replication, the result is an unpredictable change in the nucleotide sequence of an organism's DNA. This process, called mutation, is part of what determines changes in the characteristics of populations across multiple generations.
Although most DNA sequences encode information that is used to make the proteins that travel throughout cells, some sequences are only intended to make proteins that stay inside the nucleus and monitor the DNA itself. These sequences often serve as binding sites for special regulatory proteins that manage the process of transcription.
Heredity, or the continuity of traits between parent and offspring, is powered by the physical transmission of DNA between cells during reproduction. In this unit, you will learn about the origins of our modern understanding of heredity, as well as the basic rules that determine how parents’ traits determine the traits of their offspring.
Introduction: How Is Genetic Information Passed between Organisms?
In this unit, you will learn about the origins of the modern field of genetics. In particular, you will discover how an organism's traits are inherited from its parents through transmission of genes contained in parental DNA. You will also explore the complex set of rules that shape the ways in which parental traits determine which traits are observable among offspring.
Each Organism's Traits Are Inherited from a Parent through Transmission of DNA
By the mid-nineteenth century, scientists began to realize that traits were inherited due to the passage of some substance from parents to their offspring, but they were not sure what that substance was or where it was located. We now understand that this substance is DNA. Learn how scientists discovered that DNA and its chromosomal forms carry the traits observed through generations of organisms.
Inheritance of Traits by Offspring Follows Predictable Rules
After tracking physical characteristics of the common pea plant through multiple generations, Gregor Mendel realized that inheritance follows specific patterns. Mendel’s discovery led to what we now call the principles of inheritance. In this page, you will begin to learn about these principles, which lie at the heart of modern genetic analysis.
Some Genes Are Transmitted to Offspring in Groups via the Phenomenon of Gene Linkage
At the beginning of the twentieth century, some scientists noted that different inherited traits seemed to be linked — in other words, these traits were often found together in organisms. In this page, you will learn where the phenomenon of gene linkage originates and how it operates.
The Sex of Offspring Is Determined by Particular Chromosomes
During cell division in most organisms, DNA is packaged into multiple chromosomes — each of which has its own purpose — before being transmitted to the offspring cells. Of these chromosomes, one particular set has the purpose of determining the sex of these offspring. In this page, you will learn how chromosome-based sex determination works in different types of organisms.
Some Organisms Transmit Genetic Material to Offspring without Cell Division
Some organisms — chiefly bacteria — can exchange genetic material without cell division. In this page, you will learn about transformation, conjugation, and transduction, three processes by which bacteria can exchange genes.
Although DNA is so extremely small that we are not able to see it with the naked eye, scientists have developed laboratory techniques to track DNA and even modify it. With these techniques, scientists can assess how active gene transcription is, and what conditions can change it. Scientists can also ask fundamental questions about multiple genes at the same time. In this unit, you will learn what these techniques are, how they are performed, and what they achieve.
Introduction: How Do We Study the DNA Inside Cells?
In this unit, you will learn how various phenomena of genetics — replication, transcription, and regulation — can be observed and analyzed with modern laboratory techniques. These techniques include gene sequencing, PCR, gene knockouts, SAGE, and microarray analysis.
The Order of Nucleotides in a Gene Is Revealed by DNA Sequencing
Through the technique of DNA sequencing, first developed by Frederick Sanger, scientists can determine the exact order of nucleotides in an organism’s genes. Knowing this order is the first step in our efforts to map the DNA sequences of all organisms and thereby connect gene sequence with gene function.
Scientists Can Make Copies of a Gene through PCR
With the technique called polymerase chain reaction (PCR), scientists can make multiple copies of a specific genetic sequence within DNA. PCR is a powerful tool for researchers because it allows for other types of genetic analysis that require large quantities of DNA.
Scientists Can Analyze Gene Function by Deleting Gene Sequences
There are at least thousands of genes in the DNA of most organisms, and more than 20,000 in the DNA of each human being, for instance. How can we determine which genes lead to which observable traits? Scientists have developed techniques that delete individual gene sequences from an organism’s DNA. By observing the impact of this deletion on the entire biological system of an organism, scientists can connect previously unknown genes to their function.
Gene Expression Is Analyzed by Tracking RNA
Through laboratory techniques that track quantities of mRNA, scientists can identify which genes are “turned on” and which are “turned off” in an organism’s tissue at a given time, as well as how vigorously these genes are expressed. This enables scientists to understand the time course of gene expression and the impact of environmental conditions on multiple genes. In this page, you will learn about two techniques that track RNA, Northern blot and SAGE.
Scientists Can Study an Organism's Entire Genome with Microarray Analysis
An organism’s genome — or the full set of information encoded in the organism’s DNA — may include over 20,000 distinct genes. Until recently, scientists could analyze genes with a variety of techniques, but only one or a few at a time. Due to the development of microarray analysis, scientists are now able to study an organism’s entire genome at once. In this page, you will learn how microarray analysis works by studying a specific experimental example.
Because DNA passes from parent to offspring, there is generally significant genetic similarity between the organisms in a population, provided that the members of this population have descended from common ancestors. For example, although human beings have existed for 200,000 years, there is a less than 0.1% difference (called genetic variability) between the DNA of even the most dissimilar human beings. Nonetheless, the collective genetic makeup of entire populations can change significantly over time. The study of how this happens among both humans and other organisms is called population genetics. In this unit, you will learn how the underlying genetic variability of a population emerges, as well as how and why the collective genetic makeup of a population can change.
Introduction: How Does Inheritance Operate at the Level of Whole Populations?
In this unit, you will learn how the underlying genetic variability of a population emerges. You will also explore the mechanisms by which the collective genetic makeup of a population changes over time.
The Collective Set of Alleles in a Population Is Its Gene Pool
A gene pool is the collective set of genes found across all organisms in a population. In this page, you will learn about variation within gene pools, as well as the ways in which this variation can be an advantage to populations of organisms.
The Variety of Genes in the Gene Pool Can Be Quantified within a Population
Through a combination of observation and mathematical estimation, scientists can evaluate the amount of genetic variation in different populations. Upon doing so, they can then analyze differences in genetic variation over time and through changing environmental conditions. In this page, you will learn the basics of these scientific techniques.
The Genetic Variation in a Population Is Caused by Multiple Factors
There are many different forces that power genetic variation within a population. These forces, which may be gradual or sudden, include the environment and the behavior of the population. In this page, you will learn what mechanisms lead to genetic variation and ultimately contribute to either the development of new species or the disappearance of existing species.
Genomics Enables Scientists to Study Genetic Variability in Human Populations
Scientists are intrigued by genetic variation among their own kind: human beings. As scientists make advances in the techniques of genomics — the use of modern analytical tools like computers to process large amounts of genetic information — they are increasingly able to ask broader questions, analyze larger samples, and draw more salient conclusions about how genetic variation in human populations has operated over the past 200,000 years. In this page, you will learn about some of the ways in which genomic techniques have been applied to the study of the human species.
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