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Karen Williams

Ch. 11 Mendelian Genetics Genotype and Phenotype -the characteristics of an individual are traits (also called characters) -Traits are under the control of genes -the genetic constitution of an organism is called its genotype and the phenotype is an observable trait or set of traits of an organism produced by the interaction between its genotype and the environment -phenotype may be visible measurable -genes provide only the potential for developing a particular phenotype -the extent to which that potential is realized, in many cases, depends on environmental influences and random developmental events -in other words, genotypes set the range of possible phenotypes, while the environment determines where in that range the phenotype ends up -effects of the environment vary Mendel’s experimental design -the work of Mendel is considered the foundation of modern genetics -discovered some fundamental principles of genetics -from the results of crossbreeding pea plants with different traits, Mendel developed a simple theory to explain the transmission of hereditary traits from generation to generation 0generally genetic crosses with eukaryotes are done as follows: two diploid individuals are allowed to produce haploid gametes by meiosis. Fusion of male and female gametes produces zygotes from which the diploid progeny individuals are generated. -organism suitable for use in genetic experiments: it is easy to grow, bears flowers and fruit in the same year a seed is planted, and produces a large number of seed -stemns: male reproductive organs. Pistils: female reproductive organs -the pea normally reproduces by self-fertilization (also called selfing) -cross fertilization (or cross) is the fusion of male gametes (in the case of mendel, pollen) from one individual and female gametes (egg) from another -true-breeding or pure-breeding strains: strains in which the trait under investigation remained unchanged from parent to offspring for many generations. HOMOZYGOUS Monohybrid Crosses and Mendel’s Principle of Segregation -parental generation is the P generation -the progeny of the P mating is the first filial generation, F 1 -the subsequent generation produced by breeding together the F offspr1ng is the F gener2tion (second filial generation) -monohybrid crosses: crosses between true-breeding strains of peas that had alternative forms of a single trait -reciprocal crosses: example wrinkled female x smooth male -Principle of uniformity in F1: the finding that all offspring of true-breeding parents are alike -called genes, factors -each factor (gene) was considered to exist in alternative forms (alleles) each of which specified one of the traits -dominant (masks) and recessive (masked) -dominant traits -dominant alleles -homozygoous: two copies of the same specific allele of a particular gene -heterozygous: two different alleles of a particular gene -punnet sq. -Mendel made some general conclusions about his data 1. the results of reciprocal crosses were always the same 2. the F1progeny resembled one of the parent strains, indicating the dominance of one allele over the other 3. in the 2 generation, the parental trait that had disappeared in the F ge1eration reappeared. Furthermore the trait seen in the F (1ominant trait) was always found in the F at ab2ut three times the frequency of the other trait (recessive trait) The principle of segregation -principle of segregation: two members of a gene pair (alleles) segregate (separate) from each other in the formation of gametes; half the gametes carry one allele, and the other half carry the other allele -recessive traits, which are masked in the F f1om a cross between two true breading strains, reappear in specific proportion in the F .2 -specific location of a gene on a chromosome is called its locus (loci plural) -haploid: a cell or an individual with set of chromosomes Representing crosses with a branch diagram -probability: ratio of the number of times a particular event is expected to occur to occur to the number of trials during which the vent could have happened -product rule: “and”. The product rules is used for independent events. This means that the probability of one event occurring is unchanged by the outcome of the other event. The probability of both events occurring is the product of their individual probabilities -sum rule: “or”. The sum rule is used for mutually exclusive events. The probability that an event and the alternative event will occur is given by summing their probabilities Confirming the Principle of Segregation: The use of testcrosses -testcross: a cross of an individual expressing the dominant phenotype with a homozygous recessive individual to determine its genotype Wrinkled-Pea Phenotype -functional allele of agene that predominates in the population of an organism found in the “wild” is called the wild-type allele -loss-of-fu
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