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11 1 2012-h

11 1 2012-h






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    11 1 2012-h 11 1 2012-h Presentation Transcript

    • DNA is copied when mitosis or meiosis beginsdna dna+protein chromatin copied chromatin chromosome
    • Chromosomes & Chromatids
    • Chapter 11Introduction to genetics
    • Genetics (遗传学)• The study of heredity
    • Some terms in genetics• Traits (性状) – The features inherited from the parents – May have different forms – Determined by genes Red flowers White flowers
    • Some terms in genetics• Genes (基因) – Unit of heredity – Definition: A heritable factor that controls a specific characteristic
    • Some terms in genetics• Locus (plural: loci) B b– The position of the gene on the chromosome
    • Some terms in genetics• Alleles (等位基因) B b– Different versions of the same gene– Eg: B- brown eye, b- blue eye
    • Some terms in genetics• Homologous chromosomes (同源染色体)• Two chromosomes, one from each parent, that look the same.• They carry the same genes but not necessarily the same alleles.
    • Homologous chromosomes& Sister chromatids
    • A pair of homologouschromosomesA gene locusA pair of allelesThree pairs of genes
    • Some terms in genetics• Some traits mask others – purple & white flower colors are separate traits that do not blend I’ll speak for • purple x white ≠ light purple both of us! • purple masked white – dominant allele Dominant allele leads to production of mutant allele leads to no pigmen – masks other alleles purple pigment – recessive allele – shows effect when dominant homologous allele is absent chromosomes
    • Some terms in genetics• Homozygous = same alleles on the homologous chromosomes= PP, pp• Heterozygous = different alleles on the homologous chromosomes = Pp homozygous dominant heterozygous homozygous recessive
    • Some terms in genetics• Phenotype = The characteristics of an organisms• Genotype = The alleles of an organism Discussion: What is the relationship between phenotype and genotype?
    • Phenotype vs. genotype• 2 organisms can have the same phenotype but have different genotypes purple PP homozygous dominant purple Pp heterozygous
    • Some terms in genetics• P - Parent generation• ♀- female, ♂- male• F1 - First-generation offspring• F2 - Second-generation offspring P F1 F2 F3
    • Some terms in genetics• Self-pollination• The anther opens and the pollen lands on the stigma of the same flower.• Cross pollination• Anthers open on one flower and a vector (insects, wind, or animals) moves pollen to the stigma of another flower. Discussion: why a lot of plants develop strategies to prevent self-pollination?
    • Some terms in genetics• True breeding plant (纯种) – If self-pollinated, the offspring will always be same as parents P F1 F2 F3
    • Some terms in genetics• Hybrid (杂种) – The offspring of a cross between parents with different traits father hybrid mother
    • Some terms in genetics• Gamete (配子) = sex cells – Sperm and egg
    • 11-1 The Work of Gregor Mendel
    • Genetics &The Work of Mendel 2006-2007
    • Gregor Mendel• Modern genetics began in the mid- 1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas – used experimental method – used quantitative analysis • collected data & counted them – excellent example of scientific method
    • Mendel’s work Pollen transferred from white flower to stigma of purple flower• Bred pea plants P – cross-pollinate true breeding parents (P) – raised seed & then anthers removed observed traits (F1) all purple flowers result – allowed offspring F1 to self-pollinate & observed next generation (F2) self-pollinate F2
    • Mendel collected data for 7 pea traits
    • Looking closer at Mendel’s work true-breeding true-breeding XP purple-flower peas white-flower peas 100%F1 purple-flower peasgeneration 100%(hybrids) self-pollinate 75% 25% purple-flower peas white-flower peas 3:1F2generation
    • Traits are inherited as discrete units• For each characteristic, an organism inherits 2 alleles, 1 from each parent – diploid • inherits 2 sets of chromosomes (2n), 1 from each parent • haploid 1 set of chromosomes (n) What are the advantages of being diploid?
    • Making crosses• Can represent alleles as letters – flower color alleles P or p – true-breeding purple-flower peas PP – true-breeding white-flower peas pp P X ___ x ___ purple white F1 all purple ___
    • Looking closer at Mendel’s work true-breeding true-breeding X phenotypeP purple-flower peas white-flower peas ___ ___ genotype 100%F1 purple-flower peasgeneration 100%(hybrids) ___ ___ ___ ___ self-pollinate 75% 25% purple-flower peas white-flower peas 3:1F2generation ? ? ? ?
    • Aaaaah, Punnett squares phenotype & genotype can have different Pp x Pp ratiosF1generation(hybrids) % % genotype phenotype male / sperm PP ___ Pp ___ ___ female / eggs Pp pp ___ ___ ____ ___
    • Test cross• Breed the dominant phenotype — the unknown genotype — with a homozygous recessive (pp) to determine the identity of the unknown allele x How does that work? is it pp PP or Pp?
    • How does a Test cross work? x xPP pp Pp pp 100% purple 50% purple:50% white or 1:1
    • Mendel’s 1st law of heredity P• Law of segregation PP – during production of gametes(meiosis), P alleles segregate • homologous chromosomes separate p – each allele for a trait is packaged into a separate gamete pp p P Pp p
    • Law of Segregation • Which stage of meiosis creates the law of segregation? Metaphase 1Whoa!And Mendeldidn’t even knowDNA or genesexisted!
    • Monohybrid cross• Some of Mendel’s experiments followed the inheritance of single characters – flower color – seed color – monohybrid crosses
    • Dihybrid cross• Other of Mendel’s experiments followed the inheritance of 2 different characters – seed color and seed shape – dihybrid crosses Mendel was working out many of the genetic rules!
    • Dihybrid cross true-breeding true-breedingP yellow, round peas x green, wrinkled peas Y = yellow _____ _____ y = green R = round r = wrinkled yellow, round peasF1generation 100%(hybrids) _____self-pollinate 9:3:3:1F2generation 9/16 3/16 3/16 1/16 yellow green yellow green round round wrinkled wrinkled peas peas peas peas
    • What’s going on here?• The genes for different characters are on same or different chromosomes? – how do they assort in the gametes? – together or independently? On same chromosome YyRr On different chromosomes YyRr YR yr YR Yr yR yr Which system explains the data?
    • YyRr YyRr Dihybrid cross or YR yr YR Yr yR yrYyRr x YyRr 9/16 yellow round YR yr 3/16 green roundYR 3/16 yellow wrinkled yr 1/16 green wrinkled
    • YyRr YyRr Dihybrid cross or YR yr YR Yr yR yr YyRr x YyRr 9/16 yellow round YR Yr yR yr 3/16YR green roundYr 3/16 yellow wrinkledyR 1/16yr green wrinkled
    • Mendel’s 2nd law of heredity • Law of independent assortment • non-homologous chromosomes align and assort independently during meiosis yellow • classes of gametes produced in equal amounts green – YR = Yr = yR = yr round wrinkled YyRr Yr yR yR YR YR yr yr 1 : 1 : 1 : 1Yr
    • Law of Independent Assortment Which stage of meiosis creates the law of independent assortment?
    • The chromosomalbasis of Mendel’slaws…Trace the geneticevents throughmeiosis, gameteformation &fertilization tooffspring
    • Review: Mendel’s laws of heredity• Law of segregation – monohybrid cross • single trait – each allele segregates into separate gametes • established by Meiosis 1• Law of independent assortment – dihybrid (or more) cross • 2 or more traits – genes on separate chromosomes assort into gametes independently • established by Meiosis 1 metaphase1
    • Mendel chose peas wisely• Pea plants are good for genetic research – available in many varieties with distinct heritable features with different variations • flower color, seed color, seed shape, etc. – Mendel had strict control over which plants mated with which • each pea plant has male & female structures • pea plants can self-fertilize • Mendel could also cross-pollinate plants: moving pollen from one plant to another
    • Mendel chose peas luckily• Pea plants are good for genetic research – relatively simple genetically • most characters are controlled by a single gene with each gene having only 2 alleles, – one completely dominant over the other
    • Any Questions?? 2006-2007