Genetics
buttons.Introduction
Genes are short sequences of DNA. These genes offer instructions on how to make corresponding sequences of RNA. The sequences of RNA, in turn, provide instructions for how to build proteins. Proteins are the final product of gene expressions – the particular proteins built in the cells of an organism are what give an organism its traits. Genes indirectly instruct the cells on how to build proteins. The type of proteins directly determines all traits, but the genes determine the physical expression of traits. For any given physical characteristic (such as hair color), there may be multiple possible traits (such as black, brown, or blond hair). The particular trait an individual exhibits for a particular characteristic (like the black hair trait for the hair color characteristic) is known as that individual's 'phenotype'. The phenotype depends on the proteins produced, which depend on the version of the corresponding gene (DNA) that an individual possesses on their chromosomes. The term 'genotype' refers to an individual's particular DNA sequence for any particular gene. Therefore, genotype indirectly determines phenotype. The laws of inheritance can be used to predict traits in offspring. Read this section to explore the laws of inheritance in more detail. Take time to review Figures 12.3 through 12.20 and Tables 12.1 through 12.5 to examine the movement of traits from parents to offspring. After you read, you should be able to describe the exceptions of Mendelian genetics, define incomplete dominance and codominance, and explain the inheritance of the ABO blood system.
Figure 12.1 Experimenting with thousands of garden peas, Mendel uncovered the fundamentals of genetics.
Genetics is the study of heredity. Johann Gregor Mendel set the framework for genetics long before chromosomes or genes were identified when meiosis was not well understood. Mendel selected a simple biological system and conducted methodical, quantitative analyses using large sample sizes. Because of Mendel's work, the fundamental principles of heredity were revealed. We now know that genes, carried on chromosomes, are the basic functional units of heredity with the capability to be replicated, expressed, or mutated. Today, the postulates put forth by Mendel form the basis of classical, or Mendelian, genetics. According to Mendelian genetics, not all traits are transmitted from parents to offspring, but Mendel's experiments serve as an excellent starting point for thinking about inheritance.
Source: OpenStax, https://openstax.org/books/biology-2e/pages/12-introduction
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