1. Cancer is a genetic disease. Given this fact briefly explain why the followin
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Question
1. Cancer is a genetic disease. Given this fact briefly explain why the following 2 seemingly contradictory statements are true: 1) cancer is rarely directly passed on to offspring AND 2) some offspring are predisposed to develop cancer (in other words cancer runs in the family).
2. How does speciation occur? What is the importance of geographic isolation? How is this illustrated in the Galapagos?
3. What is Darwinian Medicine and how does it help us better understand medical conditions?
4 What are the dangers of small populations of a species from a genetic and evolutionary standpoint? What is the bottleneck effect?
Explanation / Answer
1. Cancer is caused by an abnormal gene that is being passed along from generation to generation. Although this is often referred to as inherited cancer, what is inherited is the abnormal gene that can lead to cancer, not the cancer itself. Only about 5% to 10% of all cancers result directly from gene defects (called mutations) inherited from a parent.
An abnormal change in a gene is called a mutation. The 2 types of mutations are inherited and acquired (somatic).
An inherited gene mutation is present in the egg or sperm that formed the child. After the egg is fertilized by the sperm, it created one cell called a zygote that then divided to create a fetus (which became a baby). Since all the cells in the body came from this first cell, this kind of mutation are in every cell in the body (including eggs or sperm) and so can be passed on to the next generation.
An acquired (somatic) mutation is not present in the zygote, but is acquired some time later. It occurs in one cell, and then is passed on to any new cells that are the offspring of that cell. This kind of mutation is not present in the egg or sperm, and so cannot be passed on to the next generation. Somatic mutations are much more common than inherited mutations. Most cancers are caused by acquired mutations.
2.
Speciation, or the evolution of reproductive isolation, occurs as a by-product of genetic changes that accumulate between two previously interbreeding populations of the same species.
The "classical" concept of speciation, built up in the 1930s, is easily summarized. In any normal species there is some geographical variation through the range of the species. Some of this must be purely random variation, but typically geographic variation has some ecological pattern to it. For example, birds may vary their nesting habits according to the trees available. Most geographic variation is the result of local adaptation to local environments, which in turn reflects some degree of genetic divergence between the separated populations. That genetic divergence will not lead to a species divergence, as long as genes flow (at some level) between the members of the species throughout their range. Gene flow is naturally much easier among individuals of a local population than between local populations, and much easier between adjoining populations than separated ones. Obviously, gene flow from neighboring populations acts against local adaptation.
Suppose now that for some reason or other there is a complete geographic separation between parts of the species range. Gene flow from the other parts of the range stops, and the separated populations evolve to suit their new, restricted environment. This encourages the genetic divergence of the separated populations, and might become so great that if the two populations were rejoined they would no longer be successful at interbreeding. [Even if limited interbreeding were still possible, the local adaptations might have become so advantageous that there would be strong selection for individuals to discriminate in order to mate preferentially with members of their local population, rather than with immigrant individuals.] The two sets of organisms have become new species. This concept, in which physical and genetic separation of populations leads to speciation, describes allopatric speciation.
3. Evolutionary medicine or Darwinian medicine is the application of modern evolutionary theory to understanding health and disease
The goal of evolutionary medicine is to understand why people get sick, not simply how they get sick. Modern medical research and practice has focused on the molecular and physiological mechanisms underlying health and disease, while evolutionary medicine focuses on the question of why evolution has shaped these mechanisms in ways that may leave us susceptible to disease.
The evolutionary approach has driven important advances in our understanding of cancer,[1]---- autoimmune disease,[2]-------- and anatomy.
4. The Bottleneck Effect occurs--------- 1. when there is a disaster of some sort that reduces a population to a small handful, which rarely represents the actual genetic makeup of the initial population. This leaves smaller variation among the surviving individuals.
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