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Sensation and Perception
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Chapter 10 / Exercise 8
Sensation and Perception
Brockmole/Goldstein
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Unformatted text preview: Basics: à Phenotype: [Observable characteristics of an organism -­‐ the visible expression of its genetic make-­‐ up.] is a description of the appearance of the organism. Ex. Any characteristic can have several phenotypes, e.g. a daffodil can have yellow flower color or orange flower color or white flower color. -­‐ If two individuals with the same phenotype are crossed through several generations and the offspring always have the same phenotype, then they are called true breeding. -­‐ If two true-­‐breeding individuals with different phenotypes are crossed, the offspring will all have the phenotype of one of the parents -­‐ this is the dominant phenotype; the phenotype which the offspring do not show is the recessive phenotype. The dominant characteristic will cover up, or mask, the recessive one, although the genetic information for the recessive characteristic is still present. -­‐ When we are describing crosses the original generation in a cross are called P [for parental], and the offspring of the P generation are called the F1 generation. The result of crosses between the F1 generation are called the F2 generation. -­‐ When two true breeding organisms are crossed the F1 are all the same. A breeding experiment where we are considering only one characteristics called a monohybrid cross. Experimental monohybrid crosses usually start with true breeding parents which have different phenotypes. In this case all the F1 will have the dominant phenotype, the F2 will have both dominant and recessive characteristics in a ratio of 3 dominant : 1 recessive. -­‐ A monohybrid cross is the study of the inheritance of one characteristic. à Genotype: Tells us which forms of genes are present, and the genes an organism has for a particular characteristic. -­‐ The different forms a gene can take are known as the alleles. Offspring receive one allele of a gene from each parent, these alleles may be the same or different. Only one of the two alleles can go into a gamete, and this is a random choice. (always two letters in a genotype) -­‐ When we are describing crosses we can save a lot of writing by letting the genes be represented by letters. The capital letter always represents the dominant form of the gene (the dominant allele). The small letter always represents the recessive allele. The genotype can then be written as two letters e.g.(Bb) or (Dd). -­‐ When we have two capital or two lowercase letters in the GENOTYPE (ex: TT or tt) it's called HOMOZYGOUS ("homo" means "the same"). Sometimes the term "PURE" is used instead of homozygous. -­‐ When the GENOTYPE is made up of one capital letter & one lowercase letter (ex: Tt) it's called HETEROZYGOUS ("hetero" means "other"). Just to confuse you, a heterozygous genotype can also be referred to as HYBRID. à Gametes: these are sex cells -­‐ All the cells of an organism contain two matching sets of chromosomes. Sex cells are called gametes. During gamete formation the number of chromosomes is reduced to a single set. Gametes have only one set of chromosomes. In sexual reproduction a male gamete (with 1 set of chromosomes) combines with a female gamete (with 1 set of chromosomes) to form the first cell of the new organism (which therefore get 2 sets). The process of the two gametes joining together is called fertilization. à Chromosome: is a large number of genes connected together and each gene controls a single characteristic. A gene can have different forms, each of which will cause a different phenotype in the organism. à Mitosis and Meiosis -­‐ cells divide and reproduce in two ways: mitosis and meiosis. -­‐ Mitosis: is the process of a cell division that results in two genetically identical daughter cells developing from a single parent. -­‐ A process of asexual reproduction in which the cell divides in two producing a replica, with an equal number of chromosomes in each resulting diploid cell. -­‐ used by single celled organisms to reproduce, it is also used for the organic growth of tissues, fiber, and membranes… it is asexual reproduction -­‐ its function is cellular reproduction and general growth and repair of the body. -­‐ all organisms -­‐ Meiosis: Is the division of a germ cell involving two fission of the nucleus and giving rise to four gametes, or sex cells each possessing half the number of chromosomes of the original cell. -­‐ A type of cellular reproduction in which the number of chromosomes are reduced by half through the separation of homologous chromosomes, producing two haploid cells. -­‐ This is found in sexual reproduction of organisms, the male and female sex cells (i.e egg and sperm) are the end result of meiosis, they combine to create new, genetically different offspring. -­‐ its function is to increase genetic diversity through sexual reproduction -­‐ humans, animals, plants, fungi à Stages of Mitosis: There are four mitotic phases: prophase, metaphase, anaphase, and telophase. Plant cells have an additional phase, preprophase, that occurs before prophase. 1. During the mitotic prophase, the nuclear membrane (sometimes called "envelope") dissolves. Interphase's chromatin tightly coils and condenses until it becomes chromosomes. These chromosomes are made up of two genetically identical sister chromatids that are joined together by a centromere. Centrosomes move away from the nucleus in opposite directions, leaving behind a spindle apparatus. 2. In metaphase, motor proteins found on either side of the chromosomes' centromeres help move the chromosomes according to the pull of the opposing centrosomes, eventually placing them in a vertical line down the center of the cell; this is sometimes known as the metaphase plate or spindle equator. 3. The spindle fibers begin to shorten during anaphase, pulling the sister chromatids apart at their centromeres. These split chromosomes are dragged toward the centrosomes found at opposite ends of the cell, making many of the chromatids briefly appear "V" shaped. The two split portions of the cell are officially known as "daughter chromosomes" at this point in the cell cycle. 4. Telophase is the final phase of mitotic cell division. During telophase, the daughter chromosomes attach to their respective ends of the parent cell. Previous phases are repeated, only in reverse. The spindle apparatus dissolves, and nuclear membranes form around the separated daughter chromosomes. Within these newly formed nuclei, the chromosomes uncoil and return to a chromatin state. 5. One final process—cytokinesis—is required for the daughter chromosomes to become daughter cells. Cytokinesis is not part of the cell division process, but it marks the end of the cell cycle and is the process by which the daughter chromosomes separate into two new, unique cells. Thanks to mitosis, these two new cells are genetically identical to each other and to their original parent cell; they now enter their own individual interphases. à Stages of Meiosis: There are two primary meiosis stages in which cell division occurs: meiosis 1 and meiosis 2. Both primary stages have four stages of their own. Meiosis 1 has prophase 1, metaphase 1, anaphase 1, and telophase 1, while meiosis 2 has prophase 2, metaphase 2, anaphase 2, and telophase 2. -­‐ In meiosis 1, a germ cell divides into two diploid cells (halving the number of chromosomes in the process), and the main focus is on the exchange of similar genetic material (e.g., a hair gene; see also genotype vs phenotype). In meiosis 2, which is quite similar to mitosis, the two diploid cells further divide into four haploid cells. Stages of Meiosis I • The first meiotic phase is prophase 1. As in mitosis, the nuclear membrane dissolves, chromosomes develop from the chromatin, and the centrosomes push apart, creating the spindle apparatus. Homologous (similar) chromosomes from both parents pair up and exchange DNA in a process known as crossing over. This results in genetic diversity. These paired up chromosomes—two from each parent—are called tetrads. • In metaphase 1, some of the spindle fibers attach to the chromosomes' centromeres. The fibers pull the tetrads into a vertical line along the center of the cell. • Anaphase 1 is when the tetrads are pulled apart from each other, with half the pairs going to one side of the cell and the other half going to the opposite side. It is important to understand that whole chromosomes are moving in this process, not chromatids, as is the case in mitosis. • At some point between the end of anaphase 1 and the developments of telophase 1, cytokinesis begins splitting the cell into two daughter cells. In telophase 1, The spindle apparatus dissolves, and nuclear membranes develop around the chromosomes that are now found at opposite sides of the parent cell / new cells. Stages of Meiosis II • In prophase 2, centrosomes form and push apart in the two new cells. A spindle apparatus develops, and the cells' nuclear membranes dissolve. • Spindle fibers connect to chromosome centromeres in metaphase 2 and line the chromosomes up along the cell equator. • During anaphase 2, the chromosomes' centromeres break, and the spindle fibers pull the chromatids apart. The two split portions of the cells are officially known as "sister chromosomes" at this point. • As in telophase 1, telophase 2 is aided by cytokinesis, which splits both cells yet again, resulting in four haploid cells called gametes. Nuclear membranes develop in these cells, which again enter their own interphases. Lecture 1 -­‐ Monday September 14 Introduction to Evolutionary Biology à Levels of Biological Organization: -­‐ Molecules: An extremely small particle or substance, especially at cellular or structural level. -­‐ Cells: meaning "small room", is the basic structural, functional, and biological unit of all known living organisms. They are the smallest unit of life that can replicate independently, and are often called the "building blocks of life". -­‐ Organisms: any contiguous living system that can react to stimuli, reproduce, grow, and maintain homeostasis, such as an animal, plant or bacterium. -­‐ Populations: are a group of individuals belonging to the same species that live in the same region at the same time, Population density is a measure of the number of organisms that make up a population in a defined area…. IMPORTANT UNIT AT WHICH EVOLUTION OCCURS -­‐ Communities: an interacting group of various species in a common location. For example, a forest of trees and undergrowth plants, inhabited by animals and rooted in soil containing bacteria and fungi, constitutes a biological community. -­‐ Ecosystems: is a community of living organisms in conjunction with the nonliving components of their environment (things like air, water and mineral soil), interacting as a system. à Questions in Evolutionary Biology: -­‐ formulate questions, which then are put into hypotheses, and then they are tested -­‐ The scope of a question is important, SMALL questions such as answering tractable questions can help contribute towards solving a big question where large questions are unlikely to be answered by simply one experiment, it requires multiple lines of evidence. Example: Why did sex evolve? – tough question -­‐ They mostly address small questions, many many small questions that with time build up to answer a big question -­‐ there are different levels of questions as well; there are trivial questions (don’t make any sense or has already been answered) -­‐ There are also different types of questions, there are how questions and there are why questions, different types of biologist answer different types of questions -­‐ How questions, involve determining the physiological or genetic mechanisms responsible for aspects of a trait (proximal questions) -­‐ Why Questions, involve determining the ecological function and adaptive significant of a trait (ultimate question) … THE CONCERN OF EVOLUTIONARY BIOLOGISTS à Approaches used in Evolutionary Biology: -­‐ a variety of approaches are used to address questions; the best studies use more than one source of evidence. 1. Observational: describe and quantify, the heart of all good evolutionary biology, it is also known as Natural History, observing and asking questions about phenomena seen in the field. 2. Theoretical: Develop models, verbal, graphical, and mathematical. After observing, now you may have hypotheses, and it can be valuable to think theoretically. Simple model, is the verbal one… it is like a narrative model of what you think is going on. You can try to turn the verbal model into a graphical model, you may draw a graph of how a certain trait effects the species…. Is it linear or non linear?, this can lead to a mathematical model 3. Comparative: obtain some data from many species, generality is the aspiration, so it is a good thing to see if what is being studied is general, often this is collecting the same data from related and unrelated species. 4. Experimental: manipulate a system to address a specific hypothesis: requires an experimental design and statistical analysis, this is very important in microbiology à Important Assumptions about evolution verified by scientific study -­‐ organisms on earth have changed through time -­‐ changes are gradual not instantaneous -­‐ lineages split or branch by speciation resulting which generates of biodiversity -­‐ All species have common ancestors -­‐ Most evolutionary change results from natural selection, the only process responsible for the evolution of biodiversity and adaption … AND ADAPTATION is therefore a product of evolution. à Biodiversity and Adaptation (product of evolutionary process) -­‐ Biodiversity is the variety of life on earth; the number and kinds of living organisms in a given area. -­‐ part of biodiversity is also genetic variability, and genetic variability within species is very important, species arise because there is genetic variability in populations through mutations, recombination, and genetic drift (if they become very different they do not mate with each other anymore) -­‐ Adaption: has two meanings; state or process, 1. Any trait or feature that contributes to fitness by making an organism better able to survive or reproduce in a given environment (noun) 2. The evolutionary process that leads to the origin and maintenance of such traits (verb) à Darwin’s Legacy and the Theory of Evolution: -­‐ the central unifying concept of biology -­‐ affects many other areas of knowledge -­‐ one of the most influential concepts of Western thought à Theodosius Dobzhansky (1900-­‐1975) -­‐ “nothing in biology makes sense except in the light of evolution” -­‐ Fruit fly geneticist and founder of the modern evolutionary synthesis -­‐ Dobzhansky helped discover that different fruit fly populations have different frequencies of two different versions of the same chromosome; chromosome A might be more frequent in one population while chromosome A' is more frequent in a neighboring population. à Approaches: * evolutionary mechanisms (microevolution): process related questions, population level, experimental work, studying natural selection and adaption in the wild and test theoretical models… process oriented and experimental -­‐ determining the ecological and genetic mechanisms responsible for evolutionary change -­‐ involve population-­‐ level studies of natural selection, adaption and speciation using diverse organisms -­‐ testing of theoretical models by experiments in the lab and field * evolutionary history (macroevolution): a historical science, how they are related to each other ancestrally. -­‐ determining evolutionary relationships of organisms in terms of common ancestry, phylogenetic -­‐ affinities of organisms provide a basis for classification-­‐ taxonomy & systematics -­‐ comparative data from many sources e.g. biogeography, paleontology, morphology, development and genomics. à BARETT LAB EXAMPLES: à Water Hycanith: -­‐ the discovery of Darwin’s missing form of water hyacinth ( water hyacinth-­‐ eichhornia Crassipes) & patterns of genetic diversity … a very serious aquatic invasive plant -­‐ novel adaption promoting outcrossing in plants -­‐ floats on lakes, drainage, and rice fields, and clones and has very attractive flowers which are pollinated by special long tongued bees. -­‐ Darwin was sent this plant, and he deduced this plant had a very complicated sexual reproductive system … they can clone and sexual reproduction, and have one mating type, he inferred there were three types but could only see two! He has found the L (long sexual organ) and M (medium sexual organ) but not the S, (they had thought it had gone extinct) -­‐ 1974 Barett was doing his PhD in the Amazon, he went wandering into a marsh and found the third type! -­‐ Founder event: All three occur together, the first two were taken, but the second was not to different parts of the world, so the genetic diversity is less. -­‐ In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. (due to cloning) -­‐ three mating types (morphs) restricted to native range; -­‐ most reproduction in the introduced range by cloning; -­‐ massive flounder event associated with human introduction to alien range à Babiana Ringens (Rat’s tail) – member of iris family -­‐ enigmatic species endemic to the Western Cape -­‐ Unusual traits include ground flowering and naked inflorescence axis -­‐ What pollinates this plant and what is the function of the rat tail?-­‐ It’s ancestors had flowers all the way up, but through mutations they have been surprised and only show up in the bottom, it has bird red flowers which usually means bird pollination, but birds do not pollinate flowers on the ground. -­‐ bird differ from how they pollinate in the new world (hovering) the Americas, and the old world (perching) … Asia, Africa, Australia, there are perching birds. -­‐ Major mutualism between the plant and its major pollinator, bird Malachite Sunbird, flies in grabs the perch, turns upside down and pollinates the flower. -­‐ Conducted a manipulative experiment in which they cut the perch off the plant, to see how the perch aids fitness, the perch less flowers received less visits, and birds did not touch the sex organs, which led to selfing (cloning) which is not good and this gives you inbreeding, but outcrossing is high with flowers with perches. -­‐ experimental removal of the perch lowers fertility and increases self fertilization -­‐ the perch is an adaption promoting plant reproductive success Lecture 2 -­‐ Darwin’s big idea and how it changed biology à The theory of Evolution & Darwin: -­‐ is the central unifying concept of biology -­‐ living things change gradually from one form into another over time -­‐ It is a very valid body of knowledge, a THEORY is not a hypothesis (a scientific theory is fact, it is not up for debate) -­‐ challenges view of special creation (= direct creation of all things in effectively their present form) à concept of a changing universe, replaced view of a static world -­‐ People used to believe the world was a very static place, but Darwin introduced the idea of dynamism (that things were constantly changing), changes which were important in understanding evolution à A phenomenon with no purpose, replaced view that causes of all phenomena had to have a purpose -­‐ Evolution was challenging for people to grasp because EVOLUTION HAS NO PURPOSE, (most people believe everything on Earth has a purpose) … it simply is and happens under the correct circumstances (if you have organisms with genetic variability arisen from mutations … evolution will occur) -­‐ Adaptation, species, biodiversity are not the PURPOSE of evolution, they are the consequences à Jean Baptiste de Lamarck (1744-­‐1829) -­‐ First to use the term evolution -­‐ linear rather than branching view of evolution -­‐ first to provide a casual mechanism...
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