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BIOL 1500
Julie Clark

172 a In diploid organisms which have pairs of homologous chromosomes an individuals genotype has two alleles at every gene locus Sum of all alleles at all gene loci in all individuals is called the populations gene poolGenotype frequencies is the percentage of individuals possessing each genotype Allele frequencies are the relative abundances of the different allelesFor a gene locus with two alleles scientists use symbols p and q to identify the two allelesAllele frequencies represent the commonness or rarity of each allele in the gene pool A gene locus with two alleles has three genotype frequencies but only two allele frequencies p and q Its because if you have only 2 alleles for a locus gene in a population those alleles can be combined 3 different waysSum of three genotype frequencies must be 1 as well as two allele frequencies 172 bIf conditions are met allele frequencies of the population never change and genotype frequencies change after one generation174 a174 b A balanced polymorphism is one in which two or more phenotypes are maintained in fairly stable proportions over many generations Natural selection preserves balanced polymorphism maintains genetic variation whenaHeterozygotes have higher relative fitnessbDifferent alleles are favoured in different environmentscThe rarity of a phenotype is advantageousaHeterozygote AdvantageWhen heterozygote for a particular locus have higher relative fitness than either homozygote it is called a heterozygote advantage Ex The HbS sickle allele The HbSHbS homozygous die because a faulty haemoglobin before reproduction thus it escapes natural selectionMalarial infections are most common in regions with sickle cell diseaseWhen malaria strikes normal individuals carrying the homozygous HbAHbA gene die because they have no protection against the disease However individuals heterozygote HbAHbS for the disease have greater immunity towards malaria because their cells can assume a sickle shape and kill the infectious bacteria while maintaining a large population of uninfected red blood cells It turns out that the heterozygotes HbAHbS have greater resistance to malaria thus natural selection preserves this harmful allele because the malariaprone areas have higher relative fitness than homozygotes for the normal HbA allele 181 Use of specific labels or signals to communicate information to organisms of the same species is commonCommunication affect inter and intra specific behaviourEx Vervet monkeys give different signals for different predatorsSimilarly scientific names are used to identify different species based on morphological behavioural and genetic features 182Biological species concept is a group of species that can successfully interbreed and produce fertile offspring One problem with the biological species concept is that it excludes species which reproduce asexuallyAnother group that it excludes is hybridization or when two species interbreed and produce fertile offspring doesnt put the offspring outside the biological species concept Ex Mules are hybrids of male donkey jack and a female horse marePhylogenetic species concept defines a group of organisms bound by a unique ancestryEcological species concept defines species as a group of organisms that share distinct ecological niche Androdioecy andromale dioeciocy male and female species consist of males and hermaphrodites which produce both sperm and eggs Ex Mangrove killifish In the gynogenetic group only females exist such as Amazon molly which mates with males of other species for fertilization This is not in the biological species concept Hybridization can occur in nature and can result in major and rapid evolutionAdvantage of sexual reproduction is genetic recombination which reduces mutations A study on Daphnia pulex a water flea which reproduces both sexually and asexually showed that the asexually reproducing organism carried a high rate of mutation than the other sexually reproducing population183 One definition of species is not used by biologistsOrganisms are products of evolution which is a dynamic processThe concept of species applies to static situations but not to all species in all situationsThe concept emphasizes the genetic cohesiveness of species populations of same species are said to experience gene flow that mixes their genetic material and holds the species together and genetic distinctness individuals of different species reproduce isolated so they cant exchange information but produce fertile offspring Are these speciesThe morphological species concept explains why organisms look alike Using the similarities and differences in morphological traits as convenient markers of genetic similarity or reproductive isolation biologists assume that similar phenotypes are coded by similar genotypes Morphological species concept is the idea that all individuals of a species share measurable traits that distinguish them from individuals of other species Ex Paleontology and field guides in natural history 186
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