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Mendelian Genetics
Gregor Mendel conducted experiments with pea plants to study inheritance of traits. In monohybrid crosses involving one trait like flower color, he found that one factor (red color) dominated the recessive trait (white color) in the offspring (F1 generation). When the F1 plants were self-pollinated to produce F2 offspring, there was a 3:1 ratio of dominant to recessive traits. In dihybrid crosses involving two traits like seed shape and color, the F1 offspring exhibited dominant traits for both. The F2 offspring showed a 9:3:3:1 ratio for different combinations of traits. Mendel's experiments established basic principles of heredity and were the foundation of classical
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Mendelian Genetics
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- 2. Gregor Johann Mendel (20July 1822 – 6 January 1884) Studied the inheritance of certain traits in pea (Pisum sativum), self- pollinated plant 2
- 3. 3 Mendel's laws Law ofsegregation: During the production of gametes the two copies of each hereditary factors segregate so that offspring acquire one factor from each parent Law of independent assortment: The laws of chance govern which particular characteristics of the parental pairs will occur in each individual offspring Law of dominance: One factor in a pair of traits dominates the other in inheritance unless both factors in the pair are recessive
- 4. 4 Mendel's laws forinheritance of traits Both the mother and father contribute equal quantity of genetic material to the child What traits will be seen in the child?
- 5. 5 Mendel' s experimentswere based on a number of visible contrasting characters like tall vs short plants, red vs white flowers, round vs wrinkled seeds, axial vs terminal position of flowers, green vs yellow coloured pod, grey vs white colour of the seed coat
- 6. 6 Factors (genes) responsiblefor these traits are present in pairs The pair factors or genes separate (segregate) out during the formation of gametes
- 7. Mendel's Monohybrid Cross Hybrid- of mixed character Monohybrid crosses of pea plants involved only one pair of contrasting characters or traits 7
- 8. The Parental Generation(P1) In the P1 generation all the plants were with red flowers Red-flowered – Dominant - hides its recessive partner White-flowered – Recessive - not exhibited in the next generation 8
- 9. 9 DOMINANT GENES CAPITAL LETTERS- RR - red flowers recessive genes small letters - rr - white flowers Two types of gametes are produced R r
- 10. 10 The generation producedby P1 generation is called as the first filial generation/ F1 generation Filial (Latin fīlius son. faithful/ dutiful/ devoted/ denoting the offspring of a cross)
- 11. First filial generation(F1) Observation: All the flowers of F1 generation were red in colour Conclusion: RED was DOMINANT over white Important: Though F1 individuals were bearing red-coloured flowers, they contained factors for white-coloured flowers too. 11
- 12. 12 Phenotype – externalappearance Genotype - genetic composition F1 generation - 'phenotypically' red but 'genotypically' hybrid F1 red-coloured plants are similar to P1 red-flowered plants in their phenotype but different in genotype
- 13. The F1 red-floweredplant possess Rr genotype and thus produce two types of gametes namely 'R' and 'r'. P gametes (red parent) R R P gametes (white parent) r Rr Rr r Rr Rr Phenotypic ratio – Rr : Rr : Rr : Rr = 1:1:1:1 Mendel continued with his experiments and allowed the F1 plants to self-pollinate in order to produce second filial generation F2. 13
- 14. Second filial generation(F2) F2 generation: Both red-flowered and white-flowered plants Phenotypic ratio - 3 red: 1 white Inference: Phenotypically there are two types of F2 plants, i.e. red and white flowered plants but Genotypically there are three types – RR, rr, Rr 14
- 15. 15 F1 gametes R r F1gametes R RR Rr r Rr rr Genotypic ratio 1RR : 2Rr : 1rr
- 16. 16 F2 pure dominants (RR) red flowers Homozygous F2pure recessive (rr) white flowers Homozygous F2 hybrid reds (Rr) red flowers Heterozygous
- 17. Mendel's Dihybrid Cross Adihybrid cross involves two pairs of contrasting characters (traits) 17
- 18. 18 Parental generation (P1) Seeds roundand yellow X wrinkled and green
- 19. 19 Parental generation (P1) Seeds round andyellow X wrinkled and green
- 20. 20 Parent dominant (RRYY) Parent recessive (rryy) Roundseed (RR) Wrinkled seed (rr) Yellow seed (YY) Green seed (yy) Gametes RY Gametes ry A pair of genes is represented by only one of its members
- 21. First Filial Generation(F1) F1 generation dihybrid Round Yellow seeds Genotype RrYy Phenotype: round yellow seeds 21
- 22. 22 P1 generation RRYYrryy Gametes RY RY ry ry F1 generation gametes RrYy RrYy RrYy RrYy RY and ry similar to P1 gametes parental combinations rY and Ry - recombinations
- 23. When F1 generationplants undergo self-pollination they give rise to second filial generation (F2). The four types of male gametes and the four types of female gametes give rise to 16 mating combinations which are shown in the Punnett square or chequer board diagram. 23
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- 27. Second filial generation(F2) 27 Phenotype No. of squares in chequerboard Phenotypic ratio Round Yellow 9 out of 16 9 wrinkled Yellow 3 out of 16 3 Round green 3 out of 16 3 wrinkled green 1 out of 16 1
- 28. 28 Generation Monohybrid CrossDihybrid Cross Parental (P1) Flowers Red X White Seeds – Round-Yellow X Wrinkled-Green Filial (F1) Phenotype Genotype All Red Rr All Round-Yellow RY Filial (F2) Phenotype Genotype 3 Red:1 White (3:1) 1RR:2Rr:1rr 9 Round-Yellow: 3 Round- Green: 3 Wrinkled-Yellow: 1 Wrinkled-Green 9(1RRYY, 2RrYY, 2RRYy, 4RrYy): 3(1rrYY, 2rrYy): 3(1RRyy, 2Rryy): 1(rryy)
- 29. 29 Please click thelinks in the next slide/s Monohybrid Cross https://www.youtube.com/watch?v=L sj-Ij53CkA-- Dihybrid Cross https://www.youtube.com/watch?v=U U7a9XFqIP0
- 30. 30 Thank you • Viewers •Std X text book MSBSHE Government of Maharashtra • Google Images • YouTube • Wikipedia Suggestions and appreciations welcome gkwagh@gmail.com