Chapter 7.1 Adaptation and Variation -organisms are constantly facing environmental challenges that limit their ability to survive -diversity within species and the interactions of organisms with their environment help explain how populations can change over time and why some species survive while others become extinct (disappear completely from Earth) Adaptations and Survival -adaptation is a structure, behavior or physiological process that helps an organism survive and reproduce in their environment -camouflage is an example of structural adaptation—helps animals blend in with their environment so predators will not be able to distinguish the organism from the surrounding environment environment -hibernation is an example of physiological adaptation adaptation—it allows animals such as bears and squirrels to survive in harsh winter climates Mimicry: A Type of Structural Adaptation -mimicry is a structural adaptation in which a harmless species resembles a harmful species in coloration or structure -for example, the viceroy butterfly is very desired by predators but the monarch butterfly is not since it does not taste good—the viceroy is very similar in structure and coloration to the monarch, predators would essentially avoid both butterflies since they would think that it is the monarch Developmentt of Adaptations Developmen -adaptations are the result of gradual, accumulative changes that help an organism survive and reproduce -the changes in characteristics are a result of random, heritable mutations in the DNA -variations are structural, functional or physiological differences between indivi duals—not all variations are adaptations -variation can be both positive and negative, depending on the environmental conditions -individuals with more helpful variations are more likely to survive and pass on the variation to their offspring -could eventually be considered a characteristic of the population -interactions with the environment are important to adaption since environments change over time -a characteristic that may not give an individual an advantage now may become become critical for survival later on as the environment or climate change The English Peppered Moth: Variation to Adaptation -prime example of how the proportions of some inherited characteristics in a populations change in response to changes in the environment -has three different variations: light grey with black dots, black and an intermediate colour -are active at night, vulnerable during the day so as they rested, they camouflaged in trees -black variety was very rare in the past, making up only 2% of the population in Manchester -recently, the populations of the black variety have drastically increased in Manchester, to 95% -in the past, the bark was light coloured, so the light grey moths were not as easily seen as the black ones, explaining the 2% population in Manchester -during the Industrial Revolution in England, soot began to cover the trees and the population of the black moths began to increase since they were now able to blend in with environment -the black genes in the moths were passed down to their offspring, increasing the environment -England enacted the clean air legislation, eventually allowing the lichen to grow on trees again, making it lighter and increasing the population of the light grey, speckled moths Variation within Species -the number of possible combinations of genes that offspring can inherit from their parents results in greater genetic variation among individuals within a population -genetic variation in a population results from the variety of genetic information in all the individuals of the population
Mutations Lead to Genetic Variation -mutations are changes in the genetic material (DNA) of an organism -mutations are the starting point of genetic variation in populations -they provide new alleles in a species and are the only source of new genetic variation -can occur spontaneously spontaneously when the DNA is copied (in S phase) before mitosis -when there is a mutation in DNA, the cell may exhibit new characteristics characteristics—the cell could die, malfunction, or even multiply more than it should, forming a tumor -not all mutations are harmful, they can even be beneficial or not affect the organism at all -some mutations do not have any effect on a cell -if the mutation occurs in the somatic cell, it will not be passed on to offspring and disappears from the population once the organism dies -only when the mutation alters the DNA in a gamete, the mutation may be passed on to future generations as a new allele Mutations Can Provide a Selective Advantage -mutations that were once not helpful, or even a disadvantage, may become advantageous advantageous in a changing environment -a selective advantage is a genetic advantage that improves an organism’s change of survival in a changing environment -for example, the water flea Daphina lives in waters around 20ᵒC and cannot survive in waters above 27ᵒC or warmer. A mutation enabled some populations populations of the Daphina to survive in waters from 25ᵒC-30ᵒC, which allowed them to reproduce when water temperatures are high Rapid Reproduction and Selective Advantage -in populations that reproduce quickly, a new allele resulting from a mutation may provide to be a selective advantage to some individuals when the environment changes -in time, the genet that provided the selective advantage can become a prevalent characteristic in the population -in some cases, can be the means of the survival of the whole population -an example of this concept is with the Staphylococcus aureus bacterium, a common bacterium that can have minor or major effects on human health, which reproduce very rapidly—under the right conditions, they can reproduce every 30 minutes. With such rapid reproduction, adaptation occurs very quickly, the bacteria are able to adapt to the changing environment on the infected individuals to survive and reproduce longer. This leads to problems in treating the infection since the adaptation of the bacteria to the environm ent may make them resistant to certain antibiotics -over time, the populations change, not the individuals
7.2 Natural Selection and Artificial Selection -natural selection is the process that results when the characteristics of a population of organisms change over many generations -occurs because individuals with certain traits survive specific environmental conditions and pass on their alleles to their offspring -for natural selection to occur, there must be diversity within a species Selective Pressure -selective pressure is when environmental conditions select for certain characteristics of individuals and select against other characteristics -those with desired characteristics tend to survive and pass on those alleles to offspring and future generations -for example, a population of young trees in a dense forest with very little light—the young trees that are able to survive in the shade will reproduce and pass on the alleles to survive those conditions
Natural Selection is Situational -fitness is the relative contribution an individual makes to the next generation by producing offspring that will survive long enough to reproduce -a high degree of fitness means that an organism will survive and reproduce, passing on its advantageous genes too its offspring -an organism with many viable offspring has high fitness, whereas an organism that has few or no offspring has low fitness Artificial Selection selection—a selective pressure exerted by humans on populations in -selective breeding is a form of artificial selection— order to improve or modify particular desirable traits biotechnology—the use of technology and organisms to produce useful products -is a type of biotechnology— -has a large impact on human survival -most foods that humans consume come from species that have been selectively bred -for example, artificial selection has resulted in cows that can produce more milk -some animals are selectively bred for appearance (eg. cats, dogs, etc.) -difference between natural selection and artificial selection is that in natural selection, the environmental conditions determine which populations populations will survive, whereas in artificial selection, humans play a role in selecting which populations are more desired -will affect the gene pools of individuals of the future populations since the genes from the surviving individuals are passed on to their offspring Artificial Selection and Food Crops -humans breed food crops to increase their nutritional value and harvest yield; also to be drought or pest resistant -downside to artificial selection is that if plants are bred to grow too quickly, they may not be able to tolerate the poor soil conditions -artificial selection must be balanced to maintain genetic variation within crops and the ability of the plants to respond to environmental change Consequences of Artificial Selection -can have both positive and negative consequences -for example, English bulldogs are bred for different traits, most commonly for their flat faces. This results in severe respiratory problems -some techniques for artificial breeding, such as genetic engineering, are used to introduce new genetic information into domesticated organisms -plants are specialized through selective breeding to produce the qualities that growers want, so plants that can been selectively bred lack genetic diversity -monoculture is extensive plantings of the same varieties of a species over large expanses of land -easier for farmers to maintain since there is only one kind of plant growing in a large field -there is also risk since the organisms are so familiar, if a new disease infests the crop, the whole population of the plants could be killed or severely damaged Gene Banks -contains populations of early ancestors of modern plants -seeds have been preserved so their genetic information for introduction into modern plants if the need arises
