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Mendel and Heredity

Mendel and Heredity. Heredity : The transmission of characteristics from one generation to the next. Genetics : The study of heredity -what characteristics get passed on, and how are they passed on?. Origins of Genetic Science Gregor Mendel (1822-1884) -Augustinian Monk, designed

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Mendel and Heredity

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  1. Mendel and Heredity Heredity: The transmission of characteristics from one generation to the next. Genetics: The study of heredity -what characteristics get passed on, and how are they passed on?

  2. Origins of Genetic Science Gregor Mendel (1822-1884) -Augustinian Monk, designed experiments to see if environment or “something else” influenced the traits of organisms.

  3. Mendel published his work on genetics in 1866, but it was largely ignored until 1900. Why was Mendel’s work ignored? His work was finally recognized as an important part of genetic research. Why was his work finally recognized?

  4. Mendel worked with large numbers of pea plants. Benefits of using pea plants: -many traits expressed on 1 plant -easy to grow in large numbers -peas reproduce sexually, recombining genes

  5. Generations Parental Generation (P) First Filial Generation (F1) Second Filial Generation (F2)

  6. Mendel’s Early Experiments -crossed peas with smooth seeds and peas with wrinkled seeds (PxP cross) -the result was plants, all with smooth seeds (F1 generation)

  7. P rr RR Smooth Peas Wrinkled Peas Rr F1 Smooth Peas

  8. Mendel then crossed F1 plants with F1 plants Rr x Rr The result was a ratio of 3 plants that produced smooth peas to 1 plant that produced wrinkled peas .

  9. Mendel’s Hypothesis: -For every trait, there are 2 factors, one from the male, one from the female. The combination of these factors determines the trait that is expressed. -(we now call the “factors” genes.)

  10. Mendel represented dominant genes with a CAPITAL letter, and recessive genes with a lower case letter. Ex: R for Round, smooth peas r for wrinkled peas

  11. Terms: Allele: One of two or more alternate forms of a gene. Example: R - round seeds r - wrinkled seeds

  12. Genotype: The combination of alleles that an organism has. Example: in peas, for seed shape, the possible genotypes are RR, Rr, and rr. Phenotype: The physical or visible features determined by the organisms genotype: Example: round peas, blue eyes, tallness

  13. Homozygous: When an organism has 2 identical alleles for a trait Example: RR or rr Homozygous Dominant (RR) Homozygous Recessive (rr) Heterozygous: When an organism has 2 different alleles for a trait Example Rr

  14. Mendel’s 2 Laws: 1) Law of Dominance- One form of a hereditary trait, the dominant trait, dominates or prevents the expression of the recessive trait.

  15. 2) The Law of Segregation: During gamete formation, the pair of genes responsible for each trait separates so that each gamete receives only 1 gene for each trait.

  16. Punnett Squares -allow us to predict the outcome of the combination of possible gametes Gametes A A A AA AA Aa Aa a

  17. Incomplete Dominance -neither allele is dominant to the other -three phenotypes result, with the third being intermediate to the other two

  18. Example: In some flowers, the alleles for flower color show incomplete dominance. The allele for RED is R, the allele for WHITE is W. The resulting cross of 2 homozygous individuals would be: RR x WW

  19. RR x WW (PxP cross) RR= Red Flowers WW= White Flowers R R W RW RW F1 W RW RW RW= Pink Flowers

  20. RW x RW(F1xF1 cross) RR= Red Flowers WW= White Flowers R W R RR RW F2 W RW WW RW= Pink Flowers

  21. Crosses with 2 traits EX: Tall/Red x short/white T= Tall t = short R=Red r= white Parent Genotypes: TTRR x ttrr Both are homozygous

  22. Things to remember: 1) alleles for traits always sort independently. 2) gametes MUST have one allele for each trait.

  23. TTRR x ttrr (P x P cross) Possible Gametes: TR TR Possible Gametes: tr tr

  24. Possible Gametes TR TR tr TtRr TtRr TtRr TtRr tr

  25. F1 cross (TtRr x TtRr) TtRr TtRr Possible Gametes: TR Tr tR tr Possible Gametes: TR Tr tR tr

  26. TR tR tr Tr TR TTRR TtRR TtRr TTRr Tr TTRr TTrr TtRr Ttrr TtRr ttRr tR TtRR ttRR tr TtRr Ttrr ttRr ttrr

  27. Codominance -Codominance is similar to incomplete dominance, because neither allele is dominant to the other. -But it is different, because instead of an intermediate trait, being shown, both traits are exhibited.

  28. Example: Blood types Type A Type B Type AB Type O

  29. There are 3 alleles for blood type. A,B,and O A and B are codominant O is recessive to both A and B Phenotype A B AB O Genotype AA , AO BB , BO AB OO

  30. AO x AB A O A AO AA B BO AB

  31. AO x BO A O B BO AB O OO AO

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