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Date Created: 09/17/15
GENETICS amp DEVELOPMENT Physical Basis of lnheritability Cell Division Cell Reproduction cells reproduce identically yet with variation new traits quotAll living cells arise from preexisting cellsquot Genetics asks how at cellular amp molecular level Development reveals the life cycle of organisms 1 gametic cells divide gt egg amp sperm cells 2 reproduction mechanisms of organisms fertilization 3 growth of organism zygote to adult cell differentiation differential gene activity totipotency amp cloning METHODS of CELL REPRODUCTION Fission binary 2 equal halves bacteria Budding outgrowths detach new organism Asexual Mitosis identical cell copies Sexual Meiosis produces sperm amp egg 3142007 Bil 150 7 Cell Division Asexual Cell Division duplication of DNA amp division of chromosomes liver cells 1xyr vs epithelial cells 1xday CELL CYCLE Life Cycle of a Cell 3 Stages lnterphase between successive divisions 3 parts GI before DNA synthesis 5 amp GZ period after Cytokenesis physical division of cell into two parts Nucelar Division Phase MITOSIS Stages of Mitosis lnterphase DNA chromatin duplicates Prophase chromatin condenses each homolog has 2 chromatids IVIetapnase chromosome align at equator homologs align independently separates chromatids of homolog Anaphase MT attach to kientochore pu chromatids apart Telophase chromosome decondense mm mm time determination of stages done by PulseChase exp 3142007 Bil 150 7 Cell Division ekremelemn m w Chromosomes bacteria 3000 genes 1 chromosome human 25000 genes 46 chromosomes Genes occur in chromatin of nucleus which condense into CHROMOSOMES at time of cell reproduction Human has 46 chromosomes 23 HOMOLOGOUS pairs in mitotic division each homolog has 2 chromatids which separate into 2 cells 3142007 Bil 150 7 Cell Division Control of Cell Division amp Cell Cycle 2001 Nobel prize Regulated by quotGrowth Factorsquot proteins that promote cell division MPF mitotic promoting factor a protein complex of cdk cyclin MPF is a kinase enzyme ones that switches onoff target proteins by phosphorylating them inactive gt activeP ATP gt ADP MPF promotes mitosis by phosphorylating other proteins including ones that leads to destruction of cyclin itself cdk another cell division control protein a cyclin dependent kinase active only when bound to cyclin cyclin a protein whose amount varies cyclically when in high concentrations binds to cdk makes MPF cyclin cdk MPF favors Mitosis Cell Division is also regulated via critical CHECK POINTS 1 Gl checkpoint cell size adequate polymerases 2 62 Checkpoint chromsome replication successful 3 metaphase checkpoint chromosome attached to spindle fibers 3142007 Bil lin Cell Division 4 SEXUAL CELL REPRODUCTION meiosis Where does meiosis occur in sexual cell reproduction haploid gametes gt fertilization gt diploid chrm 46 meiosis gt haploid gametes half chrm 23 nm Stages of Sexual Cell Division are same as asexual interphase cytokinesis nuclear but 2 Divisions Meiosis I amp Meiosis ll 1 2 4 cells Names of stages are same amp have analogous functions Prohase I chromosomes condense Metaphase I chromosomes align at equator homologs PAIR together synapsis crossover exchange at chiasmata Anaphase I chromosomes migrate toward poles Telophasel chromosome at poles Meiosis I gt separated homologs of homologous pair Meiosis II is just like mitosis gt separates chromatids of one homolog of a homologous pair 3142007 Bil 150 7 Cell Division Comparison of MitosisMeiosis mitosis separates chromatids meiosis seapartaes homologs then chromatids n A Crossing Over exchange of chromosome material Pnmmiumlm chumInna mum cnmmmwmm cmulnuw hymn nomulwzu wmmmm WE FNLWT Q i Pawns I n J Mm m mm m Mmmsz ii quotmmmmquot munm 11 MEYAPHASEI rwn m 424 r 7 M w 7 mmquot mm maula f 4 uninitiated 7 i mmmnme 2 A k J aosisll 2 DAumrrEn can 7 n 4 OF Mrrcsls DAIIGNTEI Eu cinnamon 4 mm mmmml npumn um mumquotd m and man u ZMZDW an 1507 Ceii ow SUMMARY OF MEIOSIS 1 Nuclear division phase of sexual cell reproduction 2 Two successive divisions results in 4 daughter cells Meiosis 1 and Meiosis 2 3 Reductiondivision occurs 4 cells halve the number of parent cell chromosomes diploid gt haploid 4 Stages have same nomenclature as Mitosis prophase metaphase anaphase telophase M1 amp M2 5 Only one S phase where DNA is duplicated often is no interphase between M1 and M2 6 Homologs separate in Meiosis 1 chromatids separate in Meiosis 2 mitoticlike 7 Random Assortment occurs homologs align at equitorial plates independent of each other 8 Crossing over may occur in Prophase l synapsis close pairing of homologs to allow exchange chiasmata points of exchange of sister chromatids Consequence of sex new genechromosome combos that did not exist in either parent which will become the stuff of evolution 3142007 Bil 150 Cell Division J Science of HEREDITY Mendelian Genetics is the study of the form morphology and appearance phenotype of an organism as established by its genes amp influenced by environment Essence of heredity ability of a cell to faithfully copy its DNA instructions into identical progeny cells Mendelian Genetics quantitative analysis of inheritance in organisms experiments which established the basic principles amp laws that predict the pattern of inheritance from generation to generation Molecular Genetics physical properties of molecules DNA amp RNA as they effect patterns of inheritance Central Dogma of Molecular Biology DNA transcription gt RNA translation gt Protein 3152007 all 150 Mendelian Genetics Mendelian MONOHYBRID Cross produces progeny from an experimental genetic cross between true breeding parents homozygous for a single genetic character with 2 different phenotypes appearances Parental round seed x wrinkled seed F1 round seed x themselves F2 3 round seed to 1 wrinkled seed Mendel39s 7 true breeding traits in crosses of pea plants Mendel s Particulate Inheritance Inheritance is discernible as quotparticlesquot lfactorsquot which are discrete entities w own integrity no blending of traits preserved through inheritance occur within the individual in PAIRS diploid some particles mask expression of others Mendel s Law of Segregation when gametes are formed 2 particles in an individual segregate from each other each gamete receives 1 particle from each parent 3152007 Bil 150 Mendelian Genetics ix Interpretation of Mendel s results Particles are GENES definable in molecular terms referred to by alpha taxonomy A and a B and b etc occur in different forms called alleles alleles a gene which codes for different forms of a similar protein that governs the character trait or enotype each individual possess 2 alleles for a speci c trait homozygous dominant Rr heterozygous rr homozygous recessive alleles occur on chromosomes at GENE LOCI a corresponding area on each chromosome each individual possess 2 chromosomes homologs one from each arent maternal homolog the chromosome from the mother paternal homolog the chromosome from the father um lm yummy k 7 3mm WI Traits can mask expression of others dominance amp recessive recessive trait that disappears in the F1 generation dominant trait that does not disappear in the F1 3152007 Bil 150 r Mendelian Genetics Parental RR x rr cross pollinate round wrinkled R r F quot T gametes R r R F1 Rr r self pollinate R 139 F2 0 egg 0 0 r R 0 39 r H 0 1 sperm PHENOTYPE 3 round to 1 wrinkled GENOTYPE 1RR 2Rr 1 rr Mendel39s hypothesis basically is that the F1 is heterozygote Testcrossbackcross 3152007 Bil 150 Mendelian Genetics Link between Phenotype starch content starch grains hold water amp swell reducing sugar UDPglucose hos hor ase phenotype amp genotype RR round high numerous low high starch 61 gt starchn1 thus Rr round median median median median rr wrinkled dry seed low few high low R gene codes for an enzyme UDPglucose phosphorylase which makes starch that is hygroscopic and absorbs water making the seed appear round in the dry seed state or wrinkled if the gene is recessive Also gibberellic acid gene 3152007 Bil 150 r Mendelian Genetics Dihybrid cross Independent Assortment flower color seed color P1 F1 F2 parental nonparental nonparental parental Each trait alone DOMINANT RECESSIVE W red w white G green g yellow WWGG x wwgg Wng x Wng self cross phenotypes flower seed red green 9 of 16 white green 3 of 16 red yellow 3 of 16 white yellow 1 of 16 red 12 of 16 white 4 of 16 green 12 of 16 yellow 4 of 16 3 to 1 NEW COMBINATION NOT SEEN IN PARENTS TRAITS SORT INDEPENDENT of EACH OTHER genes occur on DIFFERENT CHROMOSOMES 3152007 Bil 150 Mendelian Genetics Mendel s Law of Independent Assortment Dihybrid Cross involves 2 characters or traits new combinations of traits not exhibited by either parent parentals progeny look like parents nonparentals progeny don39t look like either parent traits are distributed into progeny independent of each other therefore genes must occur on different chromosomes Incomplete Dominance neither gene is dominant both are needed to express the trait Chromosomal Theory of Inheritance gt Sutton 1903 looked at spematogenesis in grasshoppers discovered meiosis hereditary traits are carried in sperm amp egg cells on chromosomes chromosomes obey Mendel39s laws chromosomes occur in pairs as quotparticlesquot chromosomes segregate at meiosis as particles members of chromosome pair sort independently 3152007 Bil 150 r Mendelian Genetics CHROMSOMAL LINKAGE Thomas Hunt Morgan U of Columbia geneticist fruit fly genes amp their traits are linked on specific chromosome SEX chromosomes X and Y heterogametic sex amp homogametic sex AUTOSOMES nonsex chromosomes KARYOTYPE photographic map of a species chromosomes SEX LINKED Recessives amp HEMIZYGOUS Cells X3 X3 vs X3 Y ex red green colorblindness males 8 and females 1 hemophilia albanism myopia Duchenes39 MD Autosomal Linkage two traits are carried on a single chromosome do not sort independently crossing over will allow us to map position of genes mapping frequency of cross over exchange is proportional to relative distance between 2 genes 3152007 Bil 150 Mendelian Genetics 8 Y chromosome is much smaller than its homolog the X chromosome holds only a dozen or so genes X holds 20003000 genes involved in male fertility codes for testes proteins many are repeat am lified holds some quothousekeeping genesquot 139 amp genes with homology to the quotXquot 1 fig holds lots of quotjunkquot DNA amp STR39s Short Tandem Repeats holds a gene SRY sex determining region encodes a protein that triggers formation of testes by activating genes on several autosomes X amp Y evolved from a matching pair of autosomes some 240 to 320 millions years ago tips of X amp Y can engage in recombination but rest of Y can not the degeneration of Y chromosome occurred after evolution of SRY gene because of a loss of ability to recombine during meiosis without recombination genes on Y mutated stopped working amp degenerated 3152007 Bil 150 r Mendelian Genetics 9 Barr Body an Inactive Xchromosome XX 2 doses of gene activity while Xy 1 dose of X genes yet expression of males amp females is about the same HOW an inactive Xchromosome in mammals is common one of the 2 XX39s becomes transcriptionally inactive which X is inactive seems to be randomized In interphase cells the inactive Xchromosome is visualized as a dark chromatin spot amp is called a BARR BODY Inactivation of the X chromosome occurs due to chromatin condensation via 1 methylation of 539Cysteine 2 presence of chromatin proteins that promotes heterochromatinization 3 presence of a single gene on one X that is active Xist gene only lightly methylated gt makes RNAi interference RNA not a mRNA XistRNAi binds to Xchromosome from which it is transcribed amp favors inactivation of Xchromosome once inactivated all progeny cells are also inactivated How do active Xchromosomes prevent the action of RNAi antiXist gene called Tsix is involved Tsix makes an RNAi that binds complementarily to the RNAiXist molecule making a double stranded RNA amp thereby inactivating it from protein synthesis 3152007 Bil 150 Mendelian Genetics 10 Gene 1 Gene 2 o Gene 3 LInked genes crossrng over Ger94 GENE 5 amp mappmg Gene 6 Gene 7quot F1 RYry round and yellow 8323 3 Gene 1U Testcross RYry x ryry 32 if linked ry if nonlinked ry mixed RY RYry RY RYry RrYy rv rvrv Rv erv Rrvv rY rYry rrYy rv rvrv rrvv 11 1111 BUT we do a F1 testcross and actually get round amp yellow 415 RY parental wrinkled amp green 415 rryy parental round amp green 85 Ryy nonparental wrinkled amp yellow 85 rrY nonparental HOW CROSSING OVER 3152007 Bil 150 Mendelian Genetics 11 a b Frequency of crossover exchange is GREATER the FARTHER apart 2 genes are Frequency of exchange is proportional to relative distance between 2 linked genes 1 crossover frequency 1 map unit of distance 1 CrossOver 1 centiMorgan Genes R and Y reveal 17 CO frequency of exchange thus genes are 17 map units centiMorgans apart R Y 17cm Genes R and X reveal 5 crossover frequency Genes Y and X can reveal either 12 or 22 3152007 Bil 150 Mendelian Genetics 12 Some gene interactions Complimentary Genes mutually dependent on two genes for phenotype expression Purple flower color amp protein compliment P PPCC x ppcc F1 PpCc F2 9 PC purple 3 ppC white 9 7 3 CCP white not 9331 1 ccpp white Epistasis works in similar fashion c melanin gene but a gene at one locus alters the phenotype of other gene at a second locus altered dihybrid ratio 9 CB 3 Cbb 3 ccB 1 ccbb black brown white Polygenic Inheritance 2 more genes affect 1 phenotype quantitative characters height weight etc Pleiotropy 1 gene influences many henot ic traits mutant defect in collagen gene deformity 3152007 Bil 150 Mendelian Genetics 13 Some Human Genetic Traits Pedigree Analysis symbols femaleO male D Unaffected Unaffme Affected Unaffected male lemme male innrain Widow39s peak finger hair freckles free ear lobes Blood Groups 4 phenotypes O A B and AB due to RBC surface carbohydrates Polygenic Inheritance multiple genes gt 1 phenotype usually quantitative traits w normal dist Linkage 2 genes on same chromosome autosomes vs sex chromosomes karyotypes Sex linkage trait carried on Xchromosome redgreen colorblindness carrier heterozygote XRXIr XRY can we have a colorblind femalesome crosses 3152007 Bil 150 Mendelian Genetics Some more Human Genetics 1 lnborn Errors of Metabolism defective enzymes PHENYLKETONURIA PKU pp 1 18000 disfunctional phenylalanine hydroxylase PHE gt PHEpyruvate gt gt degraded amp excreted accumulates bloodbrain barrier mental retardation ALKAPTONURIA aa Garrod in 1908 homogentisic acid oxidase gt ALKAPTON lst suggestion effect of genes was oxidizes black to make proteins disease defective TAY SACHS tt 1 300000 defective lysosomal enzyme swell burst gt death Ashkenazic Jews show 1 3600 births 1 28 is Tt SICKLE CELL ss 1 6000 births defective beta polypeptide of Hb improper folding of Hb gt clogs capillaries 2 Chromosomal Abberations Mistakes of Meiosis aneuploidy variations in chromosome due to nondisjunction which can lead to Downs Syndrome chromosome 21 and a number of sex chromosomes syndromes 3152007 Bil 150 Mendelian Genetics 15 Aneuploidy Variation in chromosome monosomy 1 less than normal disomy normal diploid trisomy 1 more than normal Aneuploidy in the sex chromosomes Gametes XX gt O amp JXXl amp X or X Y I X Y X0 Y0 XXX XXY Turner Syndrome dies Triple X Kleinfelter 1 5000 1 1000 1 2000 female appearance meta female appear male sterile no visible symptoms sterile may be retarded Eugenics euploidy amp criminal inheritance XYY of 197 violents 7 were XYY Richard Speck Chicago nurse serial killer Amniocentesis monitoring for genetic defects 3152007 Bil 150 Mendelian Genetics 16 HardyWeinberg Equilibrium population genetics 1908 uIIHaray English mathematician GWeinberg German physician Law of Genetic Equilibrium describes gene pool ie all alleles present mathematically defines ideal case of a NONevolving populations criteria must be used in large populations large sample sizes which exhibit random mating absence of forces which can change allele frequencies no migration inout no mutation no selection each allele is equally viable no lethals law states gt original percentage of a genotypes alleles remain constant HW is defined algebraically by the binomial expansion any gene with 2 allelic form A amp a then frequency of one allele A p amp frequency of other allele a q then by definition p q 1 HW equation pq2 p2 2pq q2 66 Gg gg 3152007 Bil 150 Mendelian Genetics In population of Canettes Orange is domlnant GG to Green gg of 1000 Canettes 40 are Green gg amp 960 are Orange GG or Gg q2 freq homozygous recessive green gg 004 401000004 x 1000 40 q freq of recessive allele 004 020 p freq domlnant allele G 1 q 1 01 U8U 2pq freq of heterozygote 2 02 03 032x1000 320 q2 freq of homozygous dominant 032 064 x 1000 640 cystic fibrois example 3152007 Bil 150 r Mendelian Genetics Definitions of a Gene Mendel39s Particles a unit of heredity responsible for a phenotype Morgan39s Loci placed gene on a chromosome ie it is a cellular entity part of a chromosome Watson amp Crick is a region of specific nucleotides along length of a DNA molecule Modern Molecular Biology functional definition DNA sequence coding for a specific polypeptide Split Genes lntrons amp Exons eukaryotic genes contain noncoding segments with no corresponding proteins Others any definition should also include promoter sequences enhancers segments that code for rRNA tRNA amp snRNP39s quotA GENE is a region of DNA that CODES for an RNAquot 3152007 Bil 150 Mendelian Genetics 19
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