The Y chromosome has been likened to a hall of mirrors because its sequence contains many sections that appear to be palindromes. These palindromes provide a clue to some interesting events that may have occurred during the course of the chromosome's evolution.
Slippage during DNA replication can lead to expanding sections of repeating nucleotides. Watch this animation to see how this problem occurs.
When two different strains of influenza infect a single cell, their genetic material can mix freely, resulting in a new third strain of influenza.
Meiosis, the form of cell division unique to egg and sperm production, sets the stage for sex determination by creating sperm that carry either an X or a Y sex chromosome. But what is it about the X or Y that determines sex?
This animation illustrates how mistakes made during DNA replication are repaired.
PCR is a standard laboratory technique that allows amplification of specific segments of DNA based on complementarity.
This animation shows how the protein MECP2, in conjuction with another protein complex, can act as an "on-off' switch for gene expression.
DNA's chemical properties can be harnessed for a variety of biotechnology applications.
General transcription factors, activators, and repressors interact to regulate the transcription of eukaryotic DNA into RNA.
Adenine (A), cytosine (C), guanine (G), and thymine (T) are the components of nucleic acid that make up DNA.
In 1950, Erwin Chargaff published a paper stating that in the DNA of any given species, the ratio of adenine to thymine is equal, as is the ratio of cytosine to guanine. This became known as Chargaff's ratio, and it was an important clue for solving the structure of DNA.
Of the 3 billion letters in the human genome, only 1% directly code for proteins. Of the rest, about 25% make up genes and their regulatory elements. The functions of the remaining letters are still unclear.
Reactive molecules, such as free radicals, and solar ultraviolet radiation can lead to mutations in DNA. Most mutations are corrected, but in rare cases mutations can accumulate and cause diseases such as cancer.
A new gene can be inserted into a loop of bacterial DNA called a plasmid. This is done by cutting the plasmid DNA with a restriction enzyme, which allows a new piece of DNA to be inserted. The ends of the new piece of DNA are stitched together by an enzyme called DNA ligase. The genetically...
The human genome is organized into structures called chromosomes, consisting of 22 matching pairs and one pair of sex chromosomes.
The public Human Genome Project started by identifying unique marker sequences distributed throughout the genome. Then, many copies of a small section of DNA were randomly cleaved into smaller fragments, and each small fragment was sequenced. Because there were originally many copies of the DNA...
DNA is tightly packed in the nucleus of every cell. DNA wraps around special proteins called histones, which form loops of DNA called nucleosomes. These nucleosomes coil and stack together to form fibers called chromatin. Chromatin in turn forms larger loops and coils to form chromosomes.
DNA has a double helix structure. If untwisted, DNA looks like two parallel strands. Each strand has a linear sequence of A, C, G, and T. The precise order of the letters carries the coded instructions. One strand is a complementary image of the other: A always pairs with T, and C always pairs...
One of the failed hypothetical models of DNA is Linus Pauling's triple helix model. This structure would be unstable under normal cellular conditions.
Polymerase chain reaction, or PCR, is a technique for making many copies of a specific DNA sequence. DNA is repeatedly heated and cooled in the presence of primers that bracket the desired sequence and of the enzyme Tac polymerase. In as few as 30 cycles, a billion copies of the target sequence...
The structure of DNA, discovered by James Watson and Francis Crick, suggests a mechanism of replication. The double helix unwinds, and each strand acts as a template for the construction of the new DNA molecule.
Using information from molecular research, this 3-D animation shows how DNA is replicated at the molecular level. It involves an enzyme that unwinds the DNA, and other enzymes that copy the two resulting strands.
Both strands of the DNA double helix act as templates for the new DNA strands. Incoming DNA is unraveled by the enzyme helicase, resulting in the 3' strand and the 5' strand. The 3' strands and the 5' strands are replicated by a DNA polymerase enzyme but in different ways.
Fred Sanger developed the first technique for sequencing DNA. DNA is replicated in the presence of chemically altered versions of the A, C, G, and T bases. These bases stop the replication process when they are incorporated into the growing strand of DNA, resulting in varying lengths of short...
In shotgun sequencing many copies of the entire genome are "blown up" into millions of small fragments. Each small fragment is sequenced. Powerful computers then assemble the individual fragments into the original configuration. Repeat sequences pose a problem for this approach because their...
During the process of trying to elucidate the structure of DNA, Jim Watson made some cardboard models to try to understand how DNA nucleotides are paired. It helped him visualize how hydrogen atoms of paired nucleotides interact with each other to form a symmetrical structure that fits the...
“The Assemblers” (Peter Skewes-Cox and Dr. Graham Ruby) sing about DNA and proteins.
Genetic evidence shows that humans evolved in Africa and continue to evolve.
Watch two leading virus researchers explain how they use both simple and sophisticated technologies to detect and fight infectious agents.
New technologies like the Virochip harness DNA's properties to identify and fight new viruses.
Dr. Ganem analyses the complex causes of epidemics—how changes in the environment and in human social behavior can give rise to new infectious diseases.
Although there are numerous kinds of cancer, all stem from alterations that allow cell division to outstrip cell demise.
In four presentations, Stuart L. Schreiber, PhD, and Eric S. Lander, PhD, open a window onto the fast-paced world of genomic science and chemical genetics.
Dr. Lander explores human genetic variation and how it may affect individual susceptibility to certain diseases.
The chromosome ends, or telomeres, are necessary for DNA stability and replication.
Scientists have pieced together the evolutionary history of the Antarctic icefish. The icefish makes an excellent case study for genetic evolution as both the gain and loss of genes have led to key adaptations.
The lab will familiarize you with the science and techniques used to make transgenic flies to study circadian rhythms.
This virtual lab will familiarize you with the science and techniques used to identify different types of bacteria based on their DNA sequences.
This Click and Learn explains how DNA sequences can be used to generate such trees, and how to interpret them.
Learn the principles of how DNA is sequenced and assembled into whole genomes using the Sanger method, shotgun sequencing, or ultra-deep sequencing.
How both gene chips and microarray slides are created.
This mini-lesson covers the research on telomeres that has happened since the 1995 Holiday Lectures.
Learn about what p53 does, and how interfering with its function can lead to cancer.
The following classroom-ready resources complement The Making of the Fittest: The Birth and Death of Genes, which describes how scientists have pieced together the evolutionary history of the Antarctic icefish. The icefish makes an excellent case study for genetic evolution as...
To accompany the lecture series Potent Biology: Stem Cells, Cloning, and Regeneration.
Topics include: PCR, DNA Sequencing, Genetic Engineering, and Microarray. This guide includes multiple classroom-ready worksheets to accompany HHMI’s virtual labs.
Topics include: DNA structure and function, DNA replication, damage to DNA and eukaryotic chromosomal structure.
Interactively explore topics in biology with the Click and Learn app. Now available from the Apple App Store,...
The Double Helix is the story of the scientists and evidence involved in one of the most important scientific quests of the 20th century: the discovery of the structure of DNA.
The following classroom-ready resources complement The Double Helix. This short film describes the evidence that led James Watson and Francis Crick to the discovery of the double-helical structure of DNA and how the structure immediately revealed how genetic information is stored and...