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Biology Final Keywords.docx

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AlleleOne of two or more versions of a gene Different alleles can result in different observable phenotypic traits alleles represent the genotype Each trait has 2 alleles one allele for diploid organisms Genetic variations in alleles can result in differences also can be unnoticeable due to recessive and dominant alleles Allele frequencies The abundance of one allele relative to others at the same gene locus in individuals of a population to describe genetic diversity Can be calculated by dividing the number of alleles for a certain traitthe total number of individuals in the population usually expressed as proportion or a percentage Allopatric speciation A reproductive isolating mechanism that results from geographical separation between two populations resulting in a prezygotic mechanism organisms are unable to form a zygote Populations evolve independently and diverge into different species this can be caused by glaciers continental shifts etc Allopolyploidy Having 2 or more complete sets of chromosomes from different parent species Only plants are capable of surviving with this condition not animals In the case of plants it results in a fertile hybrid Can be created from previously sterile species ex bread wheat Autopolyploidy Having 2 or more complete sets of chromosomes from the same parent speciesOnly viable in plants through self fertilization Arises through a failure in the meiotic processThese offspring often resemble parents except grow more slowly and flower later Behavioural Isolation A prezygotic isolation processTwo species do not mate because of differences in courtship behaviour also known as ethological isolationex songs of bullfrogs fireflies example used in class sequences of bursts of light vary for different species of fireflies within males and females Beneficial mutation A mutation that proves to be beneficial for the individual ie increases fitnesscan help withstand diseases improves fertility improves efficiency etcex 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 offspring A reproductively isolated gene pool However there is no universally agreed upon definitionproblems with the concept how do you define a fossil species How do you define populations that reproduce asexually Ex archaea and bacteria Bottleneck Effect A type of genetic drift that occurs when an event such as drought or intensive selection pressure causes a population to significantly dwindle in size The survivors reproduce but there is limited genetic variabilityex elephant seals tomato taste Chromosomal Inversion a chromosome rearrangement in which a segment of a chromosome is reversed end to end occurs when a single chromosome undergoes breakage with itself This occurs in the arm of the chromosome does not involve the centromere A type of mutation that does not usually cause abnormalities as long as the rearrangement is balanced with no extra genetic information however increased production of abnormal chromatids result in heterozygous individuals with lowered fertility due to production of unbalanced gametes A mutation involving theChromosomal translocation rearrangement of parts between nonhomologous chromosomesie a piece of one chromosome breaks off and sticks to another chromosomeThere are two types reciprocalRobersonianReciprocal Two 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 segments this is the major source of genetic variability It occurs during prophase I in a process known as synapsis Matching regions on matching chromosomes break and then reconnect to the other chromosomeDeleterious mutation A genetic mutation that proves to be harmful for the organism Causes errors in the protein sequence making a partially functional or completely nonfunctional protein When the protein plays a critical role in an organisms 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 two sets of chromosomes Grow through cell division mitosis and reproduce by meiosis production of gametesex animalsDirectional selection A type of selection in which individuals at one extreme of the phenotypic expression have a higher fitness this results in the frequency of the favoured phenotype becoming highereventually fixed This occurs most often naturally under environmental changesex breeding for the most desirable trait ie the smallest possible ChihuahuaDisruptive selection A type of selection in which extreme phenotypes have higher fitness than intermediate phenotypes This results in speciation it is the driving force behind sympatric speciationex different species of birds with very long and very small beaksDominant allele An allele that expresses its phenotypic effect even when heterozygous with a recessive allele Important for masking recessive phenotypespreserving recessive alleles in a population Also important when a detrimental mutation is present in a recessive form a dominant allele will prevent the expression of the harmful alleleex if the pea plant is dominant for green seeds and recessive for yellow seeds and the individual is heterozygous then the green seed phenotype will showEcological isolation a prezygotic isolation mechanismspecies that live in the same geographic region occupy different habitats
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