is comprised of all chemical, physical, and biological features of the earth than can affect or be affected by human activities.

Environmental exposure

occurs in a variety of ways: in different settings (e.g., the home, the workplace), through different routes (e.g., foods), because of different activities (e.g., chores, hobbies), or because of unique or critical times in the lifespan.


is used when referring to the social expression of living with one or two X chromosomes.

Gender differences

are primarily determined by non-biologic factors, such as social roles, but influenced by sex-steroid hormone metabolism, anatomy, immunologic function, and genetic influences.


are the fundamental physical and functional unit of heredity. A gene is an ordered sequence of nucleotides located in a particular chromosome that encodes a specific functional product.

"knockout" mice

are experimental mice created by disrupting (knocking out) the function of a specific gene.

MAP-2 kinase

is an enzyme that transduces growth factor pathways.

Multiple sclerosis

is an autoimmune disease of the central nervous system that attacks the myelin sheath surrounding nerve fibers in the brain and the spinal cord.


is a permanent, transmissible change in the DNA sequence. It can be an insertion or deletion of genetic material or an alteration in the original information.


are naturally occurring variations in a DNA sequence. Polymorphisms are useful markers because they allow researchers to distinguish between DNA of different origins.


is generally used to designate the chromosomal or biologic phenomena linked to having one or two X chromosomes. Normal females have two X chromosomes, while normal males have one X chromosome and one Y chromosome.


is the state of being readily affected or acted upon by the environment. The impact depends on exposure and the individual's ability to respond.


is the herbicide 2,3,7,8-tetrachlorodibenzo-p-dioxin, a known carcinogen and hormone disrupter in rats.

Transgenic mice

are mice that have a foreign gene introduced into their cells.

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