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BIOLOGY NOTES FOR EXAM 4- How do the chromosomes move along the spindle?o Inside centromere is the kinetochore, which moves along the spindle, destroying it as it goeso “walking” along spindle breaking it down- What determines when a cell divides?o Cells do not continuously divideo Cancer – cells dividing when they’re not supposed too When a cell dies, it is replacedo Checkpoints during cell cycle G1 checkpoint When cell receives no-go, moves into G0 phaseo Components of Cell Division Regulation Cyclin – a protein that varies in concentration depending on the cell cycle- None in G1- Low concentration in S- High concentration in G2- Cyclin destroyed at the end of cell division CDK – Cyclin Dependent Kinase, remains in constant concentration- Always there, all through interphase MPF – Maturation Promoting Factor- Triggers cell to go from G2 to Mitosis- Present during cell division, only when there is a high concentration of Cyclin and presence of CDK (combination of the two in a molecule)- How many chromosomes are required to have one copy of each gene?o Or how many chromosomes are required to have one complete copy of all the DNA needed to code for every protein in an organism? It doesn’t matter It could be on one chromosome, or as many as is needed Meaningless, only number of sets matters- Ploidyo Number of sets of chromosomeso Haploid = 1 set 1n 1 chromosome of 1, 2, 3, etc.o Diploid = 2 sets 2n 2 copies of each geneo Triploid = 3 sets 3n Generally really bad Not viableo Tetraploid = 4 sets 4no Polyploid versus Aneuploid Polyploidy- More than two sets of chromosomes Aneuploidy- Cells that have different number of chromosomes, not in number of sets- Change in the number of a single chromosomeo Ex., Down’s Syndrome (chromosome 21 [3 chromosomes])o Homologous Chromosomes Same length Same centromere position Same banding pattern Same genes- Meiosiso Produces non-identical daughter cellso Not identical to each othero Not identical to parental cellso Half the number of chromosomeso Why only half the number of chromosomes? Because of sexual reproductiono Does it matter which chromosomes are in each daughter cell? Yes, so you end up with two copies of each gene- Prophase Io Homologous chromosomes in synapsis Together Ex., chromosome 1a and 1b are togethero Not connected at centromere Arms are touchingo Tetrad formation Four molecules of DNAo Chiasmata Where they connecto Crossing over Exchange of the ends of the arms of the chromosomes- Metaphase Io Pairs of chromosomes line up in the middle of the cell- Anaphase Io Pairs separatedo One set to each daughter cell- Telophase Io Chromosomes [no longer pairs] near poles of cell- Cytokinesis Io Nucleus forms around each non-pair- Meiosis IIo Prophase II Chromosomes replicated No homologous pairso Metaphase II Line up on metaphase plateo Anaphase II Replicated chromosomes split apart Homologous pairs againo Telophase II Homologous pairs near poleso Cytokinesis II 4 daughter cells [haploid]- Two Important Eventso Segregation The homologous chromosomes separate into different daughter cellso Independent assortment The pairs of chromosomes assort independently from one another- A cell in G1 of the cell cycle contains 12 chromosomes in homologous pairs. It undergoes Meiosis, during Anaphase I each cell would contain?o 12 chromosomes with 6 pairs- Life Cycleso Alternation of generations Organisms with multicellular haploid and diploid stages- Inheritanceo Reproduction What is the outcome of asexual?- Identical offspring (mitosis) What is the outcome of sexual?- Different offspring (meiosis)o Key point What is the role of the parent?- Produce gametes What type of cell division produces gametes?- Meiosis- Genetic Definitionso Gene Information (DNA sequence) leading to a particular characteristico Allele One form of a geneo Locus The location of a gene on a chromosomeo Phenotype The physical expression of the alleles (purple flowers)o Genotype A listing of alleles for an individual Often for just one or two geneso Homozygous The condition in which both alleles for a gene are the sameo Heterozygous The condition on which the alleles for a gene are different- Gamete Formation Ruleso An allele can be present in a gamete only if that individual has that alleleo For every pairs of alleles an individual gamete only gets oneo Different pairs of alleles assort independently from one another- Mendel’s Observationso One trait disappeared in the F1so The recessive trait reappeared in the F2 generations and always in a 3:1 ratio- Mendel’s Explanationo Heredity is determined by discrete factorso These occur in pairs, except in gametes where there is only one from each pair- Two purple flowered pea plants are crossed and the offspring include both purple and white flowered plants. What are the genotypes of the parents?o Both heterozygous- Test Crosso Cross an individual of unknown genotype with a homozygous recessive individualo Which phenotype are we not sure of the genotype? Dominanto If the unknown individual is homozygous dominant P P/P x p/p Gametes P/p Offspring all purpleo If the unknown individual is heterozygous P P/p x p/p Gametes P,p p Offspring P p- Some purple, some white- Dihybrid Cross: Seed Form and Seed Coloro P round, yellow wrinkled, green (phenotype)R/R Y/Y r/r y/y (genotype)R/Y r/y (gametes)o F1 all round yellow (phenotype)R/r Y/y (genotype)R/Y; R/y; r/Y; r/y (gametes) o F2 round, yellow 315Wrinkled yellow 101Round green 108Wrinkled green 32o 9:3:3:1 ratio- Mendel’s Observationso New non-parental combinationso 3:1 ratio for each traito Conclusions This results from two separate and independent monohybrid crosses- Linked Geneso Genes that are on the same chromosomeo They do not assort independently- Dihybrid Cross (Assuming Linked Genes)o P phenotype round yellow x wrinkled greenGenotype RY/RY ry/ryGametes RY ryo F1 genotype RY/ryPhenotype all round yellow seededGametes RY or ry- Product Lawo The chance that independent events will occur simultaneously is equal to the product ofthe chances that they will occur separately- Variations on Mendel’s Themeo Incomplete dominance The heterozygous individuals have a phenotype intermediate to the homozygous individuals Red x white  pinko Multiple alleles Individual (diploid): no


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LSU BIOL 1202 - EXAM 4

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