Chapter 9 Populations.pdf

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Biology - Biological Sciences
BSC 3096

Chapter 9 Populations Tuesday, July 16, 2013 3:18 PM 1. Mendeloan concepts a. Mendel found that when he corssed purple flowered plants with white floweredplants, the first filial, F1 generation, produced purple flowers b. He called the purple trait dominant and the white trait rescessive c. Mendel examined seven traits in all, and each trait proved to have dominant and receesive alternatives i. d. When Mendel self-pollinated the F1 generation, the F2 generation expressed both the dominant and recessive traits in a 3-1 ration, now referred to as the Mendelian ration e. When the F2 generation the self-pollinated, 33% of the dominants (1 out of the 3 purple flowers of F2)produced only dominants (because all it had was PP) and the rest of the dominants produced the Mendelian ratio (like the F1 self-pollination) f. The white flower plants produced only white flowered plants i. Thus, half of the F2 generation expressed the dominant trait with the recessive trait latent g. The expression of a trait is phenotype, and an individual's genetic makeup is the genotype h. In completedominance, for any one trait, a diploid individual will have two chromosomes each containing a separate gene that codes for that specific trait (homologous) i. Their corresponding genes are located at the same locus ii. Each gene contributes an allele to the genotype iii. However,only one allele, the dominant, is expressed i. Mendel's first law of Heredity, the Law of Segregation, states that alleles segregate independently of each other when forming gametes i. Any gamete is equally likely to possess any allele ii. Also, the phenotypic expression is not a blend, just the expression of the dominant allele allele j. Mendel's Second Law of Heredity, the Law of independent assortment,states that genes located on different chromosomesassort independently of each other i. Genes that code for different traits (such as pea shape and color) do not affect each other during gamete formation k. Phenotypicratio of a dihybrid cross is 9:3:3:1 l. In humans, the 23rd pair of chromosomesestablishes the sex of an individual, and each partner is called a sex chromosome m. A karyotypeis a map of the chromosomes n. When a gene is found on the sex chromosomeit is called sex-linked o. For females, usually one of the X chromosomecondenses and becomes a Barr body i. Barr bodies are formed at random, so the active allele is split about evenly among the cells 2. Evolution a. The gene pool is the total of all alleles in a population i. b. Evolution is the change in the gene pool i. Even if the ratio of a certain allele temporarilychanges, as long as the gene pool remains the same percent, the population has not evolved c. Most taxonomicalclassification systemsare based upon genetic similarity d. All mammalsbelong to the class Mammalia and the phylum Chordata i. All mammalsprobably share a commonancestor that they do not share with birds ii. Even though phylum Chordata, they are in the class Aves e. Over the course of developmentof an organism from embryo to adult reflects its evolutionaryhistory i. For example, the human fetus has pharyngeal pouches reflecting its gilled ancestors f. Species is loosely limited to, but not inclusive of, all organisms that can reproduce fertile offspring with each other i. Another guideline for species is all organisms which normally reproduce selectivelyfit offspring in the wild ii. Organisms of different species may be prevented from producing fit offspring by such things as geographic isolation, habitat isolation (live in the same location but have different habits), seasonal isolation (mate in different seasons), mechanical isolation, gametic isolation, developmentalisolation (fertilized embryo develops improperly, hybrid inviability or sterility, selective hybrid elimination,and behavioral isolation (different mating rituals) g. In order to survive, the membersof the same species will exploit their environmentin a unique manner not shared by any other species called a niche h. There are two opposing reproductive strategies i. R-selection 1) Producing large numbers of offspring that mature rapidly with little or no parental care 2) Generally have high brood mortality rate 3) Population growth cu
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