This animation shows how the random deactivation of one of the X chromosomes in a pair can lead to a mozaicism in the expression genes.
Somatic cell nuclear transfer (SCNT) is a technique for cloning. The nucleus is removed from a healthy egg. This egg becomes the host for a nucleus that is transplanted from another cell, such as a skin cell. The resulting embryo can be used to generate embryonic stem cells with a genetic match...
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?
In the stickleback fish, pelvic-fin reduction resulted from changes in the regulatory switch elements of the Pitx1 gene. In the marine ancestor, the Pitx1 gene is activated in the pelvic-fin region during development to generate the fin. In the pelvic-reduced stickleback, the...
This animation shows how MIX-1 facilitates both chromosome condensation and dosage compensation.
The inner cell mass (ICM) cells of blastocyst-stage early human embryos can be removed and cultured. These cells can be grown in the lab indefinitely. Various growth factors cause these cells to develop into a variety of differentiated cells, such as muscle or nerve cells.
Cytoplasmic factors play a significant part in determining how a cell develops. This segment discusses their importance in turning the appropriate genes on and off for proper development.
The fetal brain grows enormously during pregnancy, both in terms of its size and the number of neurons it has.
As a human embryo develops, its cells become progressively restricted in the types of specialized cells that they can produce. Inner cell mass (ICM) cells of the blastocyst can make any type of body cell. Gastrula-stage cells can give rise to the cells of a given germ layer. Later, cells become...
Human embryonic development depends on stem cells. During the course of development, cells divide, migrate, and specialize. Early in development, a group of cells called the inner cell mass (ICM) forms. These cells are able to produce all the tissues of the body. Later in development, during...
A demonstration by Dr. Barbara Meyer of how a branched genetic pathway can be affected by mutations in different parts of the pathway.
Time-lapse microscopy showing cell division from 1 to 2 to 4 cell stages in C. elegans with fluorescent chromosomes.
Video of the fertilization of the C. elegans oocyte, the fusion of the egg and sperm nuclei, and the egg laying.
A growth cone contacts a repellant molecule on another axon, collapses, and withdraws.
Video microscopy demonstrating how sperm from an infertile male can be injected into a female egg.
A mini-documentary discussing the remarkable regenerative capabilities of the planarian, and how HHMI researcher Alejandro Sánchez Alvarado uses them to study the biology of stem cells.
A reduction in the level of sonic hedgehog (SHH) gene expression can lead to cyclopia.
Video microscopy of sperm motility in an average human male and an infertile male.
Doug Melton and Nadia Rosenthal are leaders in stem cell research, working primarily with mouse and human tissue. They will discuss where embryonic and adult stem cells come from and the biology of how they supply the cells the body needs.
An overview of embryonic development, the progressive differentiation of cells, and properties of embryonic stem cells.
In cloning, a cell's genetic machinery is reprogrammed. Can we similarly coax stem cells to become specific cell types?
To accompany the lecture series Potent Biology: Stem Cells, Cloning, and Regeneration.
To accompany the lecture series Evolution: Constant Change and Common Threads.
Normally the trillions of lymphocytes in the human body do not attack their host.
The poster for the 2013 Holiday Lectures on Science, Medicine in the Genomic Era, illustrates the difference between germline and somatic cell mutations.
Dr. Walsh is an HHMI investigator whose research focuses on understanding the genes involved in the development and function of the human brain.
A group of 14 stink bug eggs attached to the underside of a poplar leaf.
Many animals have a third eyelid called a nictitating membrane that protects the eye.
The young starlet sea anemone forms tentacles by cell division, migration, and shape changes.
... but that's not all they'll do. Several genes determine the diverse shapes and functions of crustacean appendages.
Most of the neurons of the cerebral cortex arise from progenitor cells that undergo repeated cell division.
Dante is a healthy 10-year-old boy who has had half his cerebral cortex surgically removed to treat his seizures.
Dr. Christopher Walsh discusses how genomic science has made enormous contributions to our understanding of the genetic causes of autism.
Dante is a 10-year-old boy born with hemimegalencephaly—an enlargement of half his brain.
Female peacock spiders stay with their young in an egg sac until they can fend for themselves.
Chromosomes change form as a cell divides to ensure that each daughter cell gets a full, intact copy of the genome.
The male peacock spider performs a spectacular dance to attract a mate—but the female is not always impressed.
The poster from the 2006 Holiday Lectures on Science, Potent Biology: Stem Cells, Cloning, and Regeneration, illustrates the role of stem cells during human embryonic development.
Zebrafish blood is generated from stem cells located in the tail region of fish embryos and later from stem cells located in the kidney of the adult fish.
Two views of a late pupa of an unidentified midge species (family Chironomidae).
This short-tailed fruit bat embryo shows a pattern of bones in its limbs characteristic of all tetrapods: one bone, two bones, lots of bones, digits.
During the larval stage, the Nemertean worm develops inside a hollow sac from which the juvenile eventually emerges, rupturing the sac and then eating the remains.