Recaputulation of mendelian genetics

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Recaputulation of mendelian genetics

  1. 1. Genetics Recapitulation of mendelian genetics & its practical application
  2. 2. What is genetics?
  3. 3. It’s a branch of science which deals with heredity & variation.
  4. 4. What is heredity ? What is variation?
  5. 5. Gregor Mendel( 1822-1884)  •Experimented with pea plants. •He thought that ‘heritable factors’ (genes) retained their individuality generation. after generation
  6. 6. Why?
  7. 7. Floral structure. Annual plant. Artificial cross pollination Hybridization experiments could be performed . It showed various contrasting characters.
  8. 8. Sr.no Character Dominant Recessive 1 Stem length Tall(T) Dwarf (t) 2 Flower colour Red (R) White (r) 3 Flower position Axial ( A) Terminal (a) 4 Pod shape Inflated (I) Constricted (i) 5 Pod colour Green (G) Yellow (g) 6 Seed form Round (R) Wrinkled (r) 7 Cotyledon Yellow (Y) Green (y)
  9. 9. Few genetic terms.  Fertilization  Gene  Alleles or Allelomorphs  Homozygous or true breeding  Heterozygous  Genotype  Phenotype
  10. 10.  Allele- The contrasting factors are called alleles.  Homozygous- These are the pure breeds.when both the factors are dominant or recessive.E.g TT or tt  Heterozygous – Hybrid which contain both allelic forms. E.g Tt  Phenotype- The external appearance of an individual.  Genotype- The genetic constitution of the plants. e.g – 1 TT : 2 Tt : 1 tt
  11. 11.  Trait - variant for a gene: i.e. a purple flower, determined by alleles  Dominant trait - expressed over recessive trait when both are present  Recessive trait - not expressed when the dominant trait is present
  12. 12. Garden Pea Experiments 1856-64 •Started with 34 kinds peas Pisium sativum •After 2 years he had 22 purebreds
  13. 13. Pea Characteristics
  14. 14. Flower Parts
  15. 15. Mendel’s Hypotheses  There are alternate forms of ‘genes’=alleles  For each trait, organisms have 2 genes, one from mom & one from dad  Pollen and egg each carry 1 allele/trait because alleles segregate  When only one allele is expressed & other has no noticeable effect, it is dominant
  16. 16. Mendel’s Experiments 1.Plants must possess constant differentiating characteristics. 2.The hybrids of such plants must, during the flowering period, be protected from the influence of all foreign pollen, or be easily capable of such protection. 3.The hybrids and their offspring should suffer no marked disturbance in their fertility in the successive generations
  17. 17. MENDEL’S LAWS LAW OF DOMINANCE . LAW OF SEGREGATION. LAW OF INDEPENDENT ASSORTMENT.
  18. 18. LAW OF DOMINANCE Tall (TT) X dwarf(tt) Gamet T X t F1 Gen - Tt(Tall)
  19. 19.  Only tallness was expressed in F1 generation as it has not allowed the expresion of dwarfness.  The character which appeared in F1 generation is called as dominant  The character that was suppressed as recessive. This was LAW OF DOMINANCE
  20. 20.  DEFINATION  LAW OF DOMINANCE STATES THAT , CROSSING BETWEEN ORGANISMS FOR CONTRASTING CHARACTERS OF A PAIR , ONLY ONE CHARACTER ( DOMINANT ) OF A PAIR APPEARS IN FIRST GENERATION i.e ONE CHARACTER (DOMINANT) PREVENTS THE EXPRESSION OF THE OTHER CHARACTER.
  21. 21. When a hybrid forms gametes, the contrasting factors or alleles segregate and enter into different gametes. The gametes formed are pure and never hybrid. Hence it is also called as LAW OF PURITY OF GAMETES.
  22. 22.  Punnet Square -F2 generation is represented in the punnet square.  Phenotypic ratio 3:1  Genotypic ratio 1: 2:1 o T t T TT(tall) Tt(tall) t Tt( tall) tt(dwarf)
  23. 23. TEST CROSS / BACK CROSS  F1 hybrid is back crossed to pure recessive parent , law of segregation should give 1 : 1 ratio in the progeny . Hybrid Tall (Tt) X dwarf(tt) Gamets , X Gamet T X t t X t F1 Gen - Tt(Tall) tt (dwarf) (Test cross between heterozygous tall & pure recessive parent) T t tt
  24. 24. 50 % of Tall  50 % of dwarf are formed 1: 1 ratio
  25. 25. The back cross is also called as test cross as it is indirect test of proportion of different types of gametes produced by F1 hybrid.
  26. 26. LAW OF INDEPENDENT STATES THAT FACTORS (GENES ) FOR DIFFERENT PAIRS OF CONTRASTING CHARACTERS ARE ASSORTED ( DISTRIBUTED OR PASSED ON) INDEPENDENT OF ONE ANOTHER DURING GAMETE FORMATION.
  27. 27. Yellow round Green wrinkled YYRR X yyrr Gamets YR X yr F1 Gen - YyRr (Yellow Round) (heterozygous )
  28. 28.  Dihybrid cross – When two pairs of characters are considered in a cross, this type of cross is known as dihybrid cross.
  29. 29. FEMALE GAMET Male gamet YR Yr yR yr YR YYRR Yellow round YYRr Yellow round YyRR Yellow round YyRr Yellow round Yr YYRr Yellow Round YYrr Yellow wrinkled YyRr Yellow round Yyrr Yellow wrinkled yR YyRR Yellow round YyRr Yellow round yyRR Green round yyRr Green round yr YyRr Yellow Round Yyrr Yellow wrinkled yyRr Green round yyrr Green wrinkled Dihybrid cross between yellow & wrinkled green plants.
  30. 30. 9:3:3:1 dihybrid ratio.

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