Suppose that a newly discovered element called centium has three isotopes that occur in nature. these are centium-200, centium-203, and centium-209. assume that these isotopes occur in equal amounts in nature. what will be the average atomic mass of this element?

Since all the isotopes occur in the same amount, to find the average atomic mass of the element, add the three mass values together and divide the result by 3. That is, 
Average atomic mass = [200 +  203 + 209] / 3 = 612 /3 = 204.
Thus, the average atomic mass of the element is 204.

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Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.

Though heredity had been observed for millennia, Gregor Mendel, a scientist and Augustinian friar working in the 19th century, was the first to study genetics scientifically. Mendel studied "trait inheritance", patterns in the way traits are handed down from parents to offspring. He observed that organisms  inherit traits by way of discrete "units of inheritance". This term, still used today, is a somewhat ambiguous definition of what is referred to as a gene.

Trait inheritance and molecular inheritance mechanisms of genes are still primary principles of genetics in the 21st century, but modern genetics has expanded beyond inheritance to studying the function and behavior of genes. Gene structure and function, variation, and distribution are studied within the context of the cell, the organism, and within the context of a population. Genetics has given rise to a number of subfields, including molecular genetics, epigenetics and population genetics. Organisms studied within the broad field span the domains of life .

Genetic processes work in combination with an organism's environment and experiences to influence development and behavior, often referred to as nature versus nurture. The intracellular or extracellular environment of a living cell or organism may switch gene transcription on or off. A classic example is two seeds of genetically identical corn, one placed in a temperate climate and one in an arid climate . While the average height of the two corn stalks may be genetically determined to be equal, the one in the arid climate only grows to half the height of the one in the temperate climate due to lack of water and nutrients in its environment.

Etymology  

The word genetics stems from the ancient Greek ' meaning "genitive"/"generative", which in turn derives from ' meaning "origin".

History  

The observation that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding. The modern science of genetics, seeking to understand this process, began with the work of the Augustinian friar Gregor Mendel in the mid-19th century.