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Chapter 9

Chapter 9. Genetics. 9.1 The Work of Gregor Mendel . Mendel – crossed pea plants to study and understand genetics Most pea plants self pollinate ( true breeding ) Mendel forced plants to cross pollinate (have 2 plants). Studied 7 traits of pea plants pg 176.

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Chapter 9

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  1. Chapter 9 Genetics

  2. 9.1 The Work of Gregor Mendel • Mendel – crossed pea plants to study and understand genetics • Most pea plants self pollinate (true breeding) • Mendel forced plants to cross pollinate (have 2 plants)

  3. Studied 7 traits of pea plants pg 176. • Took the plants that had different traits and crossbreds them (hybrids)

  4. The F1 Cross • First Filial (parent cross, produce the F1, then cross the F1 making an F2) • Law of segregation: Segregation of alleles occurs during the formation of gametes, sex cells. • Pg 177 • Law of Independent Assortment – factors for individual characteristics are not connected. Assort independently of each other.

  5. Came to 2 conclusions after the breeding • Genes, segment of DNA, occurs in pairs, controll heredity. Visual form called alleles. (noted as “factors”) • Found that some of the alleles are dominant and some are recessive. • Dominant trait always uppercase (TT, Tt) • Recessive always lowercase (tt)

  6. 9.2 Probability and Punnett Squares • Punnett square – table representation of crossing alleles • TT or tt – homozygous – same alleles • Tt – heterozygous – different alleles • Phenotype – physical look, all tall (TT, Tt) have same phenotype. • Genotype – based on alleles. (TT, and Tt) are different now.

  7. Probability • Penny = ½ = .50 • A cross results in 787 pink flowers and 277 white flowers. If we cross the same P generation, the probability will be the same)

  8. Dominant Recessive • Curled Up Nose Roman Nose • Clockwise Hair Whorl Counter-clockwise Hair Whorl • Can Roll Tongue Can't Roll Tongue • Widow's Peak No Widow's Peak • Facial Dimples No Facial Dimples • Able to taste PTC Unable to taste PTC • Earlobe hangs Earlobe attaches at base • Middigital hair (fingers) No middigital hair • No hitchhiker's thumb Hitchhiker's thumb • Tip of pinkie bends in Pinkie straight • Oval face Square face • Cleft chin no cleft chin • Broad eyebrow Slender eyebrow • Separated eyebrows Joined eyebrows • Long eyelashes Short eyelashes • Almond eyes Round eyes • Freckles No freckles • Wet-type earwax Dry-type earwax • Left thumb on top of interlocking fingers Right thumb on top of interlocking fingers

  9. Punnett Squares pg 182

  10. Homozygous x homozygous

  11. Homozygous x heterozygous • AA x Aa

  12. Hetero x hetero

  13. Summary of Mendel’s Principles pg 272 • Some alleles are neither dominant nor recessive, and many traits are controlled by multiples alleles or multiple genes. • Incomplete Dominance– when one allele is not necessarily dominant (red and white flowers produce pink) • Codominance – both alleles contribute to the phenotype. • Multiple alleles – within the population of the species there are more than just 2 types of alleles. Coloration in Rabbits • Polygenic Traits – having many genes, traits controlled by 2 or more genes. Skin color in humans.

  14. Incomplete Dominance

  15. We'll use "F" for the flower color allele. FR = allele for red flowers FW = allele for white flowers red x white -------> red & white spotted flowers FRFR  x FWFW ----> 100% FRFW

  16. Codominance • Problems

  17. Explore Punnett Squares!! • http://www.geocities.com/CapeCanaveral/Hall/1410/lab-B-19.html

  18. Dihybrid cross – two traits

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