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Tuesday March 24 By the end of class today, I should be able to: 1. Summarize cell division (m itosis & meiosis) 2. Define & apply key genetics terms 3. Predict the outcome of specific genetic crosses.
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Announcements Remember: put your phones away!
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Mitosis & Meiosis Comprehension Check If a parent cell undergoes mitosis, how many daughter cells will result? Two If that parent cell began with ten chromosomes, how many chromosomes will each daughter cells have? Ten If a parent cell undergoes meiosis I & II, how many daughter cells will result? Four If that parent cell began with 10 chromosomes, how many chromosomes will each daughter cell have? Five
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How Are Features Passed Along? 4
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5 Gregor Mendel (1822-1884) Monk given credit for discovering the Laws governing Inheritance of Traits “Father of Genetics”
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6 Mendel’s Pea Plant Experiments
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7 Mendel’s Experimental Methods Mendel hand-pollinated flowers using a paintbrush He could snip the stamens to prevent self- pollination He traced traits through the several generations
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8 How Mendel Began Mendel produced pure strains by allowing the plants to self- pollinate for several generations
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10 Mendel’s Experimental Results
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11 Generation “Gap” Parental P 1 Generation = the parental generation in a breeding experiment. F 1 generation = the first-generation offspring in a breeding experiment. (1st filial generation) From breeding individuals from the P 1 generation F 2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation) From breeding individuals from the F 1 generation
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12 Following the Generations P (parental) Cross 2 Pure Plants TT x tt F1 Results in all Hybrids Tt F2 Cross 2 Hybrids get 3 Tall & 1 Short TT, Tt, tt
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13 Genetics Terms Genes- DNAinstructions for producing a trait Genes- DNA instructions for producing a trait Alleles alternative forms of the same gene that codefor the same trait(i.e. flower color) Alleles - alternative forms of the same gene that code for the same trait (i.e. flower color)
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14 Genetics Terms Homozygous condition, both alleles are the same (e.g. PP; pp) H eterozygous condition, the alleles differ (e.g. Pp) For a given Mendelian trait, there is a dominant allele (expressed when present) and a recessive allele (only expressed when dominant absent) In a heterozygous condition, a Mendelian trait would consist of a dominant allele (D) and a recessive allele (d)
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16 Genetics Terms Genotype: The kind of alleles (genes) an organism has Phenotype: What the trait looks like Genotype: Pp Phenotype: Purple
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17 Human Mendelian Traits
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18 Human Mendelian Traits Recessive phenotype: Albinism Dominant phenotype: Achondroplasia
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19 Punnett Square Used to help solve genetics problems
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20 How to Make Punnett Square
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21 Types of Genetic Crosses Monohybrid cross - cross involving a single trait (e.g. flower color) Dihybrid cross - cross involving two traits (e.g. flower color & plant height) Polyhybrid cross - cross involving three or more traits (e.g. flower color, plant height, & pod shape…)
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22 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Round seeds x Wrinkled seeds RR x rr P1 Monohybrid Cross R R rr Rr Genotype:Rr Genotype: Rr PhenotypeRound Phenotype: Round Genotypic Ratio:All heterozygous Genotypic Ratio: All heterozygous Phenotypic Ratio: All round
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23 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Round seeds x Round seeds Rr x Rr F1 Monohybrid Cross R r rR RR rrRr Genotype:RR, Rr, rr Genotype: RR, Rr, rr PhenotypeRound & wrinkled Phenotype: Round & wrinkled G.Ratio:1:2:1 G.Ratio: 1:2:1 P.Ratio: 3:1
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24 …And Now the Test Cross Mendel then crossed a pure & a heterozygous from his F 2 generation This is known as an F 2 or test cross There are two possible testcrosses: Homozygous dominant x Heterozygous Homozygous recessive x Heterozygous
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25 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Round seeds x Round seeds RR x Rr F2 Monohybrid Cross (1st) R R rR RR RrRR Rr Genotype:RR, Rr Genotype: RR, Rr PhenotypeRound Phenotype: Round Genotypic Ratio:1:1 Genotypic Ratio: 1:1 Phenotypic Ratio: Round
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26 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Wrinkled seeds x Round seeds rr x Rr F2 Monohybrid Test Cross r r rR Rr rrRr rr Genotype:Rr, rr Genotype: Rr, rr PhenotypeRound & Wrinkled Phenotype: Round & Wrinkled G. Ratio:1:1 G. Ratio: 1:1 P.Ratio: 1:1
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27 Mendel’s Laws (Genetics Notes Part II)
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28 Law of Dominance If a dominant trait is present, it will be expressed and the recessive will not! e.g. RR x rr yields all Rr (R = round seeds)
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29 Law of Segregation “ A “Tt” parent makes an egg with “T” AND a different egg with “t”
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30 Applying the Law of Segregation
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31 Mendel: Alleles for different traits (like Tt and Pp) are distributed to sex cells (& offspring) independently of one another. Dominant Tall plants can have Dominant Red flowers OR recessive white flowers. This law applies when using dihybrid crosses. Law of Independent Assortment
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32 Summary of Mendel’s laws LAW PARENT CROSS OFFSPRING DOMINANCE TT x tt tall x short 100% Tt tall SEGREGATION Tt x Tt tall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGg round & green x round & green 9 round green: 3 round yellow: 3 wrinkled green: 1 wrinkled yellow
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33 Incomplete Dominance RrRrRrRr R Rr All Rr = pink (heterozygous pink) produces the F 1 generation r Alleles combine as unique phenotype Alleles combine as unique phenotype Example: the protein for red and protein for white are produced in snapdragons and make an intermediate color of pink.
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34 Codominance Two alleles are expressed (multiple alleles) in heterozygous individuals. All alleles equally “strong” Example: Coat color in horses Red x white
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35 Genetic Practice Problems
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36 tall (TT) x dwarf (tt) pea plants T T tt
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37 Solution: T T tt Tt All Tt = tall (heterozygous tall) produces the F 1 generation tall (TT) vs. dwarf (tt) pea plants
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38 Breed the F 1 generation tall (Tt) vs. tall (Tt) pea plants T t Tt
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39 Solution: TT Tt tt T t Tt produces the F 2 generation 1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt 1:2:1 genotype 3:1 phenotype 3:1 phenotype tall (Tt) x tall (Tt) pea plants
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40 Dihybrid Cross RYRyrYry RYRy rY ry R= round seed r= wrinkled seed Y= yellow seed y= green seed
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41 Dihybrid Cross RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy RrYY RrYy rrYY rrYy RrYy Rryy rrYy rryy Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio RYRyrYryRY Ry rY ry
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42 Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1
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