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mid-term definitions.doc

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Alleleone of two or more versions of a genedifferent alleles can result in different observable phenotypic traitseach trait has 2 allelesone allelechromosome for diploid organismsgenetic variations in alleles can result in differences also can be unnoticeable Allele frequencies the abundance of one allele relative to others at the same gene locus in individuals of a population to describe genetic diversitycan be calculated by dividing the number of alleles for a certain traitthe total number of individuals in the populationusually expressed as proportion or a percentagedenoted as p or q Allopatric speciation a reproductive isolating mechanism that results from geographical separation between two populationsa prezygotic mechanism Populations evolve independently and diverge into different speciescaused by glaciers continental shifts etc Allopolyploidy having 2 or more complete sets of chromosomes from different parent speciesonly plants are capable of this not animalsresults in a fertile hybridcan be created from previously sterile species ex bread wheat Autopolyploidy having 2 or more complete sets of chromosomes from the same parent speciesagain only possible in plants through self fertilizationarise from a failure in the meiotic processoften resemble parents except grow more slowly and flower later Behavioural Isolation a prezygotic isolation process2 species do not mate because of differences in courtship behaviouralso known as ethological isolationex songs of bullfrogs fireflies example used in class sequences of bursts of light vary for different speices of fireflies within males and females Beneficial mutation a mutation that proves to be beneficial for the individual ex increases fitnesscan help withstand diseasesex those who carry 1 allele of the sickle cell anemia disease are more resistant to malaria in areas of subsaharan Africa Biological Species the concept of a species based on the ability of populations to interbreed and produce fertile offspringbasically a reproductively isolated gene poolno universal agreement to what it isproblems with the concept how do you define a fossil specieshow do you define populations that reproduce asexually ex archaea and bacteria Bottleneck Effect Type of genetic drift that occurs when an event such as drought or intensive selection pressure causes a population to significantly dwindle in sizethe survivors reproduce but there is limited genetic variabilityNote Bottleneck different from Founder Effect In Bottleneck there is no movement of population whereas in Founder Effect there isex elephant seals tomatoe taste Chromosomal Inversion a chromosome rearrangement in which a segment of a chromosome is reversed end to endoccurs when a single chromosome undergoes breakage with itselfoccurs in the arm of the chromosome does not involve the centromeredo not usually cause abnormalities as long as the rearrangement is balanced with no extra genetic infohowever increased production of abnormal chromatids result in heterozygous individualslowered fertility due to production of unbalanced gametesChromosomal translocation rearrangement of parts between nonhomologous chromosomesie a piece of one chromosome breaks off and sticks to another chromosome2 types reciprocalRobersonianReciprocal 2 different chromosomes exchange placesRobertsonian a whole chromosome attaches to anotherEx results in Down Syndrome Trisomy 21 the 21st chromosome has 3 chromosomes instead of 2Crossing over recombination in meiosis when chromatids exchange segmentsIMPORTANCE genetic variabilityoccurs during prophase I in a process known as synapsismatching regions on matching chromosomes break and then reconnect to the other chromosome Deleterious mutation a genetic mutation that proves to be harmful for the organismcause errors in protein sequence making a partially functional of completely nonfunctional proteinwhen the protein plays a critical role in organism functioning it can be crucialie a medical condition can resultex genetic disordersare often repaired by the double checking system of DNADiploid an organism that contains 2 sets of chromosomesgrow through cell division mitosis and reproduce by meiosis production of gametesex animalsDirectional selection type of selection in which individuals at one extreme of the phenotypic expression have a higher fitnessthe frequency of the phenotype becomes higheris eventually fixedoccurs most often naturally under environmental changesex breeding for the most desirable trait ie the smallest possible ChihuahuaDisruptive selection type of selection in which extreme phenotypes have higher fitness than
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