U of M ANTH 1001 - Lecture 6 9-19-17 Genetics 2 (19 pages)

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Lecture 6 9-19-17 Genetics 2



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Lecture 6 9-19-17 Genetics 2

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Pages:
19
School:
University of Minnesota- Twin Cities
Course:
Anth 1001 - Human Evolution
Human Evolution Documents
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9 28 2017 1 Today s Objectives What Darwin did not know DNA What it is and what it does Mendelian genetics How is genetic variation achieved How is it passed to future generations 2 1 9 28 2017 Theories of inheritance The homunculus little man Augustinian monk living in Brno modern Czech Republic Did experiments with heredity in pea plants trying to breed for certain discrete traits color stem length size shape 3 Gregor Mendel 1822 1884 4 2 9 28 2017 Experiment 1 P Crossed true breeding plants for long and short stem P generation F1 F1 generation were all long stem Crossed this generation with itself F2 generation had 25 short stem 75 long stem F2 x long long short x long long long long long What does Mendel conclude from this experiment information for the short stem plant not evident in the F1 generation is still transmitted to the F2 generation P F1 short 5 x long long long F2 long long long short x long long long short 6 3 9 28 2017 Mendel s First 3 Postulates there is a 4th wait for it 1 Particles of Inheritance genes occur in pairs 1 from each parent During fertilization alleles from both parents are joined to form a pair 2 Genetic information is inherited from both parents but only one trait called dominant is expressed in the offspring 3 During gamete production meiosis homologous alleles segregate randomly into different gametes Mendell s Law of Segregation 7 What word do you associate with dominance 8 4 9 28 2017 Are dominant alleles more frequent in a population better adapted to the environment more important for individual survival normal None of the above 9 Some more definitions Heterozygous ote having different alleles at the same genetic locus AO blood type Homozygous ote having the same alleles at the same genetic locus AA blood type Dominant trait expressed in a heterozygote usually written in capital letters i e AA A blood type only need one copy to be expressed Recessive trait not expressed in heterozygote only expressed in homozygote usually written in lower case letters i e oo O blood type need 2 copies to be expressed Codominance expression of both traits in a heterozygote i e AB 10 AB blood type 5 9 28 2017 Two more Genotype genetic allelic make up of one or more gene loci For example SS Ss ss SsTt ssTt SStt Phenotype expression of a particular allele physical or behavioral characteristics For example tall brown hair O blood type 11 Know contrasting pairs Dominant Recessive also co dominant Homozygous Heterozygous Genotype Phenotype and norm of reaction 12 6 9 28 2017 Nature versus Nurture Fallacy Every trait results from the interaction of some genetic program with the environment This can be conceptualized with the idea of Canalization Every gene is canalized to varying extents i e has a norm of reaction in its expression from genotype to phenotype 13 Revisiting Mendel s 1st experiment SS x ss S homozygotes s s Ss Ss P F1 S Ss x long short long long long long Ss heterozygotes 14 7 9 28 2017 SS x ss homozygotes Ss x Ss heterozygotes F1 P x long long short long x long S S s SS Ss F2 s Ss long long long ss long short 15 What if you have more than one trait 16 8 9 28 2017 SSCC x sscc Short white Tall purple homozygotes P x long SC x sc short heterozygotes F1 SsCc x SsCc long SC Sc long sC sc SC SSCC SSCc SsCC SsCc long long Sc SSCc SScc SsCc Sscc long sC SsCC SsCc ssCC ssCc F2 17 sc SsCc Sscclong ssCc long sscc short Mendel s 4th Postulate The Law of Independent Assortment This principle was based on Mendel s experiments breeding for two different traits at once Discovered that the presence or absence of one characteristic does not effect the presence or absence of another characteristic Independent Assortment the distribution of one pair of alleles does not influence the distribution or expression of another pair 18 9 9 28 2017 SSCC x sscc Short white Tall purple homozygotes P x long SC x sc short heterozygotes F1 SsCc x SsCc long SC long Sc sC sc SC SSCC SSCc SsCC SsCc long long Sc SSCc SScc SsCc Sscc long sC SsCC SsCc ssCC ssCc F2 19 sc SsCc Sscclong ssCc long sscc short ALA 2 1 In what year did Charles Darwin publish On the Origin of Species 2 What is sexual dimorphism Provide an example i e a sexually dimorphic organism and the dimorphic feature 3 What are the 2 functions of DNA 10 9 28 2017 Do natural selection and Mendel s conclusions conflict If inheritance is particulate how can evolution take place gradually Why do phenotypes still appear to be blended How is variation maintained when natural selection culls away particular variants How is variation produced that doesn t currently exist 21 Modern Synthesis Combination of Darwin Mendel s conclusions to explain how variation is maintained 22 11 9 28 2017 The Modern Synthesis Answers Darwin s Critics 1a Before Mendel Darwin was considered wrong because blending inheritance would remove all variation 23 The Modern Synthesis Answers Darwin s Critics 1b After Mendel inheritance was understood as particulate so how can evolution result from gradual changes 24 12 9 28 2017 Monogenic and Polygenic Traits short tall 25 The Modern Synthesis Answers Darwin s Critics 1 Answer Continuous polygenic traits are controlled by many genes by way of the proteins for which they code Genes are particulate but together produce blended phenotypic traits 26 13 9 28 2017 Figure 03 05 27 Figure 03 06 28 14 9 28 2017 Figure 03 07 BMP4 BMP2 BMP7 29 Polygenic traits appear continuous but are controlled by individual genes 30 15 9 28 2017 Any Questions 31 Norm of Reaction Phenotypic range seen in individuals with a particular genotype Norm of Reaction Phenotypic Plasticity 32 16 9 28 2017 How much of a trait is genetic vs environmental FALSE dichotomy 33 Phenylketonuria PKU Autosomal recessive condition Unable to metabolize phenylalanine due to deficiency in the enzyme phenylalanine hydroxylase which breaks phenylalanine down into tyrosine Phenotypic symptoms Protein rich foods and sweeteners can act as poisons for people with phenylketonuria Diet 34 17 9 28 2017 PKU How much do genes and the environment contribute to this condition 100 genetic 100 environmental Influences aren t a simple weighted sum Allele for PKU is inherited but the phenotype need not be Genetics do not determine our fate we can construct environments appropriate for certain genetic contexts 35 Any Questions 36 18 9 28 2017 ALA 4 The norm of reaction is a The range of possible genotypes from the same phenotype because of variation in the environment b The


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