Genetics is the scientific study of heredity and the variation of inherited characteristics. It includes the study of genes, themselves, how they function, interact, and produce the visible and measurable characteristics we see in individuals and populations of species as they change from one generation to the next, over time, and in different environments.
- Chromosomes contain genetic information. We often take this fact for granted, but just over a century ago, even the best biologists in the world were uncertain of the function of these rod-shaped structures. We now know that most chromosomes contain a single molecule of double-stranded DNA that form a complex with proteins. This arrangement allows long DNA molecules to be compacted into a small volume that can more easily be moved during mitosis and meiosis and expressed during interphase.
- Before Mendel, the basic rules of heredity were not understood. For example, it was known that green-seeded pea plants occasionally produced offspring that had yellow seeds; but were the hereditary factors that controlled seed color somehow changing from one generation to the next, or were certain factors disappearing and reappearing? And did the same factors that controlled seed color also control things like plant height?
- Humans have an interesting relationship with mutation. From our perspective, mutations can be extraordinarily useful, since mutations are need for evolution to occur. Mutation is essential for the domestication and improvement of almost all of our food. On the other hand, mutations are the cause of many cancers and other diseases, and can be devastating to individuals. The vast majority of mutations probably go undetected. In this section, we will examine some of the causes and effects of mutati
- The basic concepts of genetics described in the preceding chapters can be applied to almost any eukaryotic organism. However, some techniques, such as test crosses, can only be performed with model organisms or other species that can be experimentally manipulated. To study the inheritance patterns of genes in humans and other species for which controlled matings are not possible, geneticists use the analysis of pedigrees and populations.
- The principles of genetic analysis that we have described for a single locus can be extended to the study of alleles at two loci simultaneously. Analysis of two loci in parallel is required for genetic mapping and can also reveal gene interactions. These techniques are very useful for both basic and applied research. Before discussing these techniques, we will first revisit Mendel’s classical experiments.
- Genetics is the study of the inheritance and variation of biological traits. We have previously noted that it is possible to conduct genetic research without directly studying DNA. Indeed some of the greatest geneticists had no special knowledge of DNA at all, but relied instead on analysis of phenotypes, inheritance patterns, and their ratios in carefully designed crosses. Today, classical genetics is often complemented by molecular biology, to give molecular genetics.
- This chapter examines: (1) changes in the number of whole chromosomes and how they affect the phenotype of an organism and (2) changes in the structure of individual chromosomes and how they affect meiotic pairing. Human examples will be used to show the phenotypic consequences and methods for detection.
- Cancer is a group of diseases that exhibit uncontrolled growth, invasion of adjacent tissues, and sometimes metastasis (the movement of cancer cells through the blood or lymph). In cancer cells, the regulatory mechanisms that control cell division and limit abnormal growth have been disrupted, usually by the accumulation of several mutations. Cancer is therefore essentially a genetic disease.