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Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the first of three Science Objects in the Heredity and Variation SciPack. It explores the historical perspective and experiments of Mendel.

Sexual reproduction results in the continuity of species accompanied with a great deal of variation in physical traits. One familiar observation is that offspring are very much like their parents but still show some variation— differing somewhat from their parents and from one another. People have long been curious about heredity, using even the most primitive understanding of inheritance to cultivate desirable traits in domesticated species. In the 1800s, Gregor Mendel took his observations of heredity and variation to new heights through carefully designed and executed breeding experiments that generated repeatable inheritance patterns. Mendel developed a model for explaining the patterns he observed, describing discrete units or “particles,” which both segregate and assort independently of one another during inheritance. This model offered a foundational explanation for how variation is generated through sexual reproduction. Although Mendel’s model over-simplified how traits are inherited and expressed, it set the stage for the discoveries of chromosomes and genes from which contemporary genetics grew.

• Explain how domestication of plants and animals produced an early understanding of inheritance.
• Use Mendel’s model to explain patterns of inheritance represented in graphic form (for example, data tables, histograms, etc.).
• Identify the conditions required for an inheritance pattern to be explained correctly by Mendel’s model.
• Use data representing patterns of inheritance to support the idea that some observable traits are defined by discrete units of inheritance that segregate and assort independently of one another during inheritance.

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the second of three Science Objects in the Cell Division and Differentiation SciPack. It explores the processes that take place within cells that allow for selective gene expression, which leads to the specialization and variation of cells in organisms.

Cell functions are turned on and off by regulatory genes, through changes in the activity of the functions performed by proteins. Although cells in a multi–celled organism begin alike, having essentially identical genetic instructions, selective expression of individual genes (cells are regulated) causes the unspecialized embryonic stem cells to become very different (cells can differentiate). The embryonic stem cells become increasingly more specialized, differentiating into a variety of cell types. Selective expression results when different parts of the genetic instructions are used in different types of cells, influenced by the cell's environment and past history.

The work of the cell is carried out by the many different types of molecules it assembles, mostly proteins. In specialized cells, other protein molecules may carry oxygen, effect contraction, respond to outside stimuli, or provide material for other body structures. In still other cells, assembled molecules may be exported to serve as hormones, antibodies, or digestive enzymes.

• Explain the role of regulatory genes and how they function.
• Explain how it is possible for different types of cells, such as bone cells and liver cells, to have identical genetic instructions and function differently.
• Describe the role of embryonic stem cells in the development and growth of complex organisms.
• Interpret data presented in graphs and charts from experiments addressing the role that protein-related variables (such as hormones, antibodies and digestive enzymes) play in the regulation of a complex organism’s life processes.