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 goes o walking along spindle breaking it down What determines when a cell divides o Cells do not continuously divide o Cancer cells dividing when they re not supposed to o When a cell dies it is replaced o Checkpoints during cell cycle G1 checkpoint When cell receives no go moves into G0 phase o 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 Ploidy 1 chromosome of 1 2 3 etc 1n o Number of sets of chromosomes o Haploid 1 set o Diploid 2 sets o Triploid 3 sets 2 copies of each gene 3n Generally really bad Not viable o Tetraploid 4 sets 2n 4n o Polyploid versus Aneuploid Polyploidy Aneuploidy More than two sets of chromosomes Cells that have different number of chromosomes not in number of sets Change in the number of a single chromosome o Ex Down s Syndrome chromosome 21 3 chromosomes o Homologous Chromosomes Same length Same centromere position Same banding pattern Same genes Meiosis o Produces non identical daughter cells o Not identical to each other o Not identical to parental cells o Half the number of chromosomes o Why only half the number of chromosomes Because of sexual reproduction o Does it matter which chromosomes are in each daughter cell Yes so you end up with two copies of each gene Prophase I o Homologous chromosomes in synapsis Together Ex chromosome 1a and 1b are together o Not connected at centromere Arms are touching o Tetrad formation Four molecules of DNA o Chiasmata Where they connect o Crossing over Metaphase I Exchange of the ends of the arms of the chromosomes o Pairs of chromosomes line up in the middle of the cell o Pairs separated o One set to each daughter cell Anaphase I Telophase I Cytokinesis I o Chromosomes no longer pairs near poles of cell o Nucleus forms around each non pair Meiosis II o Prophase II No homologous pairs Chromosomes replicated Line up on metaphase plate o Metaphase II o Anaphase II Homologous pairs again Replicated chromosomes split apart Homologous pairs near poles 4 daughter cells haploid o Telophase II o Cytokinesis II Two Important Events o Segregation o Independent assortment The homologous chromosomes separate into different daughter cells 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 Cycles o Alternation of generations Inheritance o Reproduction Organisms with multicellular haploid and diploid stages 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 Definitions o Gene o Allele One form of a gene Information DNA sequence leading to a particular characteristic o Locus o Phenotype o Genotype The location of a gene on a chromosome The physical expression of the alleles purple flowers A listing of alleles for an individual Often for just one or two genes o Homozygous o Heterozygous Gamete Formation Rules The condition in which both alleles for a gene are the same The condition on which the alleles for a gene are different o An allele can be present in a gamete only if that individual has that allele o For every pairs of alleles an individual gamete only gets one o Different pairs of alleles assort independently from one another o One trait disappeared in the F1s o The recessive trait reappeared in the F2 generations and always in a 3 1 ratio o Heredity is determined by discrete factors o 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 Mendel s Observations Mendel s Explanation o Both heterozygous Test Cross o Cross an individual of unknown genotype with a homozygous recessive individual o Which phenotype are we not sure of the genotype Dominant o If the unknown individual is homozygous dominant P Gametes Offspring P P x p p P p all purple o If the unknown individual is heterozygous P p x p p P p p P p Gametes Offspring P Some purple some white Dihybrid Cross Seed Form and Seed Color o P round yellow wrinkled green R R Y Y R Y r r y y r y phenotype genotype gametes This results from two separate and independent monohybrid crosses phenotype genotype gametes o F1 o F2 all round yellow R r Y y R Y R y r Y r y round yellow 315 Wrinkled yellow 101 Round green 108 Wrinkled green 32 o 9 3 3 1 ratio Mendel s Observations o New non parental combinations o 3 1 ratio for each trait o Conclusions Linked Genes o Genes that are on the same chromosome o They do not assort independently Dihybrid Cross Assuming Linked Genes o P o F1 phenotype Genotype Gametes genotype Phenotype Gametes ry ry ry round yellow x wrinkled green RY RY RY RY ry all round yellow seeded RY or ry Product Law the chances that they will occur separately Variations on Mendel s Theme o Incomplete dominance o The chance that independent events will occur simultaneously is equal to the product of o Multiple alleles o Co dominance o Sex linkage The heterozygous individuals have a phenotype intermediate to the homozygous individuals Red x white pink Individual diploid no more than 2 alleles per gene Population no more than 2n alleles per gene The heterozygote expresses both alleles phenotypes simultaneously The result of genes located on one of the sex chromosomes X or Y but not the other Examples Hemophilia red green
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