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7/11/2014 Lecture 5 What Darwin didn’t know: Mendel and basic genetics What Darwin didn’t know: Mendel and basic genetics 1. 2. 3. 4. 5. 6. 7. Family resemblance Gregor Mendel and the collapse of the blending model Mendel’s basic process Monohybrid crosses Mendel’s five element model and the principle of segregation Punnett squares Dihybrid crosses Principle of independent assortment Extending Mendel 1. 2. 3. 4. 5. 6. 7. Do peas make it too easy? Gene linkage Polygenic inheritance Epistasis Pleiotropy Incomplete dominance and codominance Environmental effects on gene expression What Darwin didn’t know: Mendel and basic genetics Another college drop out revolutionizes science! Gregor Mendel (1822-1884) and sweet peas What Darwin didn’t know: Mendel and basic genetics True breeding plants X 1 7/11/2014 What Darwin didn’t know: Mendel and basic genetics Non-true breeding plants What Darwin didn’t know: Mendel and basic genetics The basic cross X X Hybrids What Darwin didn’t know: Mendel and basic genetics The monohybrid cross What Darwin didn’t know: Mendel and basic genetics Mendel’s seven traits Terms to note: 1. 2. 3. 4. 5. P generation Cross fertilize F1 generation Self cross F2 generation 2 7/11/2014 Mendel and basic genetics The monohybrid cross Focus on the F3: 1/3 purple breed true 2/3 purple don’t What Darwin didn’t know: Mendel and basic genetics Blending inheritance does not happen! White ALWAYS breeds true! What Darwin didn’t know: Mendel and basic genetics Mendel’s five element model: 1. Parents transmit information about traits to their offspring. 2. Each individual receives two copies of each factor to encode each trait. 3. Not all factors are the same and different combinations lead to different traits. 4. The two factors do not blend. 5. The presence of a factor does not guarantee it will be expressed, it can be latent. Mendel and basic genetics Focus on the F2: Who’s a homozygote? Who’s a heterozygote? 3 7/11/2014 What Darwin didn’t know: Mendel and basic genetics Mendel’s five element model: What Darwin didn’t know: Mendel and basic genetics Which trait is dominant? 1. Parents transmit information about traits to their offspring. 2. Each individual receives two copies of each factor to encode each trait. 3. Not all factors are the same and different combinations lead to different traits. 4. The two factors do not blend. 5. The presence of a factor does not guarantee it will be expressed, it can be latent. What Darwin didn’t know: Mendel and basic genetics In this case purple is the dominant trait and white is recessive X X What Darwin didn’t know: Mendel and basic genetics Genotype AA = Aa 4 7/11/2014 What Darwin didn’t know: Mendel and basic genetics Mendel and basic genetics Phenotype Phenotype ratio = 3:1 Genotype ratio = 1:2:1 AA = Aa What Darwin didn’t know: Mendel and basic genetics What Darwin didn’t know: Mendel and basic genetics The Punnett Square Mendel’s 1st A law of heredity The Principle of Segregation – Two alleles segregate during gamete formation to be rejoined at random during fertilization. Dad a A Mom a 5 7/11/2014 What Darwin didn’t know: Mendel and basic genetics What Darwin didn’t know: Mendel and basic genetics The Punnett Square The Punnett Square In a heterozygous mom some gametes are dominant A Dad a A A Dad a A Mom Mom a a … and some are recessive What Darwin didn’t know: Mendel and basic genetics What Darwin didn’t know: Mendel and basic genetics The Punnett Square The Punnett Square A A AA Dad a A Aa Mom Dad a A AA Aa a aA aa Mom a aA aa 6 7/11/2014 What Darwin didn’t know: Mendel and basic genetics Let’s complicate things: Dihybrid crosses What Darwin didn’t know: Mendel and basic genetics Let’s complicate things: Dihybrid crosses What Darwin didn’t know: Mendel and basic genetics Let’s complicate things: Dihybrid crosses What Darwin didn’t know: Mendel and basic genetics Let’s complicate things: Dihybrid crosses Dihybrid ratios: 9/16 round yellow 3/16 round green 3/16 wrinkled yellow 1/16 wrinkled green 7 7/11/2014 What Darwin didn’t know: Mendel and basic genetics What Darwin didn’t know: Mendel and basic genetics Dihybrid crosses – 556 seeds Dihybrid crosses – 556 seeds Traits Genotype Ratios Real data Perfect data Traits Genotype Ratios Real data Perfect data Round, yellow R_, Y_ 9/16 315 313 Round, yellow R_, Y_ 9/16 315 313 Round, green R-, yy 3/16 108 104 Round, green R-, yy 3/16 108 104 Wrinkled, yellow rr, Y_ 3/16 101 104 Wrinkled, yellow rr, Y_ 3/16 101 104 Wrinkled, green rr,yy 1/16 32 35 Wrinkled, green rr,yy 1/16 32 35 Dihybrid crosses lead to 9:3:3:1 ratios Mendel had AMZINGLY good data Even still biology is just random enough that there’s some skew from perfect data What Darwin didn’t know: Mendel and basic genetics What Darwin didn’t know: Mendel and basic genetics VERY GOOD PRACTICE! Mendel’s 2nd law of heredity The Principle of Independent Assortment – In a dihybird cross the alleles of each gene assort independently. 8 7/11/2014 Extending Mendel Extending Mendel Do peas make it too easy? Do peas make it too easy? 1 Factors assort independently 1 Factors assort independently Gene linkage 2 Each trait is controlled by a single factor 2 Each trait is controlled by a single factor Polygenic inheritance 3 Factors do not interact 3 Factors do not interact Epistasis 4 Each factor only controls one trait 4 Each factor only controls one trait Pleiotropy 5 Factors only have two alternative outcomes 5 Factors only have two alternative outcomes 6 Factors are unaffected by the environment they are expressed in Incomplete dominance and codominance 6 Factors are unaffected by the environment they are expressed in Environmental effects on expression Extending Mendel Factors don’t always assort independently Genes are sometimes linked Extending Mendel Factors don’t always assort independently Genes are sometimes linked Mendel’s 2nd law of heredity The Principle of Independent Assortment – In a dihybird cross the alleles of each gene assort independently. Dihybrid ratios: 9/16 round yellow 3/16 round green 3/16 wrinkled yellow 1/16 wrinkled green 9 7/11/2014 Extending Mendel Traits can be controlled by multiple factors Polygenic inheritance Extending Mendel Traits can be controlled by multiple factors Polygenic inheritance Mendel’s traits were all two state cases Extending Mendel Traits can be controlled by multiple factors Polygenic inheritance Extending Mendel Traits can be controlled by multiple factors Polygenic inheritance 10 7/11/2014 Extending Mendel Factors can interact Extending Mendel Factors can interact Traits can be affected by more than one gene: Epistasis Traits can be affected by more than one gene: Epistasis The E gene determines presence or absence of melanin ee Extending Mendel Factors can interact EE or Ee(E_ ) Extending Mendel Factors can interact Traits can be affected by more than one gene: Epistasis Traits can be affected by more than one gene: Epistasis The B gene determines the distribution of melanin ee EE or Ee(E_ ) E_bb The B gene determines the distribution of melanin E_B_ eebb E_bb E_B_ 11 7/11/2014 Extending Mendel Factors can have multiple effects Extending Mendel Factors can have multiple effects Pleiotropy Pleiotropy A sickled blood cell Malaria entering a red blood cell Extending Mendel Factors can have more than two outcomes Extending Mendel Factors can have more than two outcomes Dominance in not always complete Dominance in not always complete Incomplete dominance: Parental phenotypes blend in the heterozygote Incomplete dominance: Parental phenotypes blend in the heterozygote 12 7/11/2014 Extending Mendel Factors can have more than two outcomes Extending Mendel Factors can have more than two outcomes Dominance in not always complete Dominance in not always complete Codominance: Heterozygotes show both parental phenotypes UNBLENDED Codominance A A A AA Type A Extending Mendel Factors can have more than two outcomes A A AA B A BA B B Type AB B B BB B Type B Example: temperature sensitive expression Codominance A A Extending Mendel The environment can affect factor expression Dominance in not always complete B A BA A A B A Type AB B B B BB B Type O Type A Type B 13 7/11/2014 Lecture 6 Chromosomes and recombination What Mendel didn’t know: Chromosomes and recombination 1. 2. 3. 4. 5. Chromosomes are discovered and come in pairs A brief introduction to mitosis and meiosis Haploidy, diploidy, polyploidy Sex chromosomes: an unusual pair Recombination via crossing over Mendel -1866 No knowledge of chromosomes, genes, DNA What does DNA do? 1. 2. 3. 4. 5. 6. Understanding how we’ve gone from factors to DNA Nucleic acids, the double helix, and a quick tour of DNA replication The central dogma (DNA =>RNA=>aa=>Protein) How central is it? Codons and translation: A universal code Closely related species have similar proteins and DNA Chromosomes and recombination Chromosomes Discovered in 1879 Chromosomes and recombination Chromosomes Chromosome number differs across taxa Linked to inheritance in 1900-1902 14 7/11/2014 Chromosomes and recombination Chromosomes Chromosomes and recombination Karyotypes Chromosome number differs across taxa Humans have 46 chromosomes total 23 from mom 23 from dad Chromosomes and recombination Terminology Chromatid Sister chromatids Centromere Homologous pair Chromosomes and recombination Karyotypes 15 7/11/2014 Chromosomes and recombination Mitosis in brief Chromosomes and recombination Meiosis in brief: Meiosis 1 (phase 1) Check out figure 11.10 in your text! Chromosomes and recombination Meiosis in brief: Meiosis 2 (phase 2) Chromosomes and recombination Meiosis in brief Start with 2x DNA Divide once normal amount of DNA Divide again half as much 16 7/11/2014 Chromosomes and recombination Ploidy = number of copies of chromosomes A cell with one copy is HAPLOID (1N) Chromosomes and recombination Ploidy Mitosis 2N 4N 2N Meiosis 2N 4N 2N A cell with two copies is DIPLOID (2N) More than two copies is polyploid (xN) 1N Check out figure 11.19 in your text! Chromosomes and recombination Sex chromosomes Chromosomes and recombination Crossing over One of these pairs is not like the others 17 7/11/2014 Chromosomes and recombination Crossing over – Another approach Chromosomes and recombination Back to gene linkage: Mom AABB Dad aabb Chromosomes and recombination Recombination leads to genetic variation Chromosomes and recombination Back to gene linkage: Mom AABB Dad aabb F1 AaBb When genes are unlinked, the F1 generation can produce four gamete combinations: F1 AaBb a A B b When traits are linked, A will not appear with b and B will not appear with a 18 7/11/2014 What does DNA do? What does DNA do? James Watson and Francis Crick, 1953, the structure of DNA Oswald Avery, Maclyn McCarty, Colin MacLeod, 1944, genes are made of DNA What does DNA do? What does DNA do? Four nucleotides: The double helix Adanine (A) Thymine (T) Cytosine (C) Guanine (G) 19 7/11/2014 What does DNA do? CTAGAGC What does DNA do? How does DNA replicate? What does DNA do? How does DNA replicate? What does DNA do? How does DNA replicate? Semi-conservatively 20 7/11/2014 What does DNA do? DNA What does DNA do? The central dogma DNA RNA RNA Protein What does DNA do? DNA The central dogma Protein What does DNA do? The central dogma The different stages of the central dogma occur in different parts of the cell Transcription RNA Translation Protein 21 7/11/2014 What does DNA do? What does DNA do? Does one gene make one protein? What is a gene? RNA Other molecules control transcription? * Always single stranded How central is the central dogma? * Uracil What role does RNA really play in the cell? Epigenetic markers? What do they do? What does DNA do? What does DNA do? What is a protein? All proteins are different combinations of 20 amino acids! 22 7/11/2014 What does DNA do? What does DNA do? All proteins are different combinations of 20 amino acids! What does DNA do? How does that work? What does DNA do? Some codons are special 23 7/11/2014 What does DNA do? What does DNA do? The universality of the genetic code is one of the strongest pieces of evidence that all living organisms share a common evolutionary heritage 5 nucleotides 20 amino acids What does DNA do? What does DNA do? Cytochrome C sequence comparisons Comparison species Number of amino acids changed Chimpanzee 0 Rhesus monkey 1 Dog 11 Rattlesnake 14 Bullfrog 18 Tuna fish 21 Fruit fly 29 Pumpkin 36 Bacteria 56 Cytochrome C 24 7/11/2014 What does DNA do? What does DNA do? DNA sequence comparisons with humans Comparison species % of genes with similar function Chimpanzee 98 Mouse 90 Fruit fly 67 Plants 33 It’s a lot to ponder 25