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Principle of Inheritance and Variation Part 2 (in Hindi)
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All important topics releated to this chapter.

Shivam Sharma
Learning and teaching Biology, pursuing medical studies at TU.

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Sir mujhe test cross smjha nhi aaya.. Plz aap kya test cross ko or aache se smjha skte hai.. plz sir
  1. PRINCIPLES OF INHERITANCE AND VARIATION


  2. MONOHYBRID CROSS Dwarf p Phenotype Tal Genotype TT Homozygous Dominant Homozygous Recessive Tt All Tall F1 Self pollinated F2 Tall is dominant Heterozygous to Dwarf Gamets Tt tall tall Tt Tall dwarf Phenotypic ratio 3:1 Genotypic ratio:12:1


  3. .Production of gametes & formation of zygotes- Punnett Square Developed by- British scientist Reginald C. Punnett Graphical representation- calculate probability of possible genotypes in genetic cross Gametes- on two sides, top row & left columns TT dwarf tall Self-pollination-50% phenotypically genotype Gametes TT* . F2-3/4th tall & 1/4th Dwarf- Fi generation TtTt Tt t Tt . 1/4 : : ratio of TT: Tt: tt- tall selfing tall Gametes T , t T, t T TTTt F2 generation


  4. Test cross: The cross between hybrid and its homozygous recessive parent I called test cross. It is used to identify the genotype of the hybrid. Dominant phenotype (allele distribution unknown) if PP if Pp P) p Homozygous recessive All offspring purple; (white) tfore unknown Homozygous recessive Half of offspring (white)white; therefore flower was homozygous unknown flower was heterozygous Alternative 1 Alternative 2


  5. MENDELIAN LAWS OF HEREDITY. .Rules were proposed- Principles or Laws of Inheritance: First Law or Law of Dominance & Second law or Law of Segregation . LAW OF DOMINANCE 1. Characters are controlled by discrete units called Factors 2. Factors occurs in pair 3. In a dissimilar pair of factors one member of the pair dominates (dominant) the other (recessive) Used to explain the expression of only one of the parental characters in monohybrid cross (F1) & expression of both in F2. Also explains proportion 3:1 in F2


  6. LAW OF SEGREGATION It states that, 'when a pair of factors for a character brought together in a hybrid, they segregate (separate) during the formation of gametes. .Alleles do not blend & both characters recovered in F2 & one in F1 Factors which is present in parent segregate & gametes receives only one of two factors Homozygous parent- one kind gamete Heterozygous parent- two kind gamete each one have one allele with equal proportion


  7. INCOMPLETE DOMINANCE: Correns discovered Incomplete dominance in Merabili:s jalapa. It is also called partial dominance, semi dominance. . The inheritance in which allele for a specific character is not completely dominant over other allele is called Incomplete dominance Snapdragon or Antirrhinum sp.- Cross between true breed red flower (RR) & white flower (rr), F1 generation- Pink (Rr) & after self pollination in F2 generation- 1 (RR) Red: 2 (Rr) Pink: 1 (rr) white Genotype ratio same as Mendelian cross & Phenotype ratio different than Mendelian cross


  8. Incomplete dominance: Ex snapdragon. (Dog flower plant)


  9. P Generation Red White Gametes F1 Generation Pink Rr Gametes 2 Eggs 2 Spermm Red F2 Generation Pink Rr Pink rR White


  10. Red X White Parent: Genotype Gametes F1 g eneration Pink (Hybrid) RW Self pollination F2 generation GametesR RW Pink wW Pink white Red RW The phenotypic ratio is The genotypic ratio is 1:2:1


  11. A and iB are co-dominant and dominant over i. Blood Group Genotype IAIA or IA i A- Group B-Group AB-Group O-Group IAIB


  12. ABO blood grouping- multiple allele . Three alleles govern same character . Multiple allele is found when population studies are made . Single gene product may produce more than one effect Eg.- Starch Synthesis in Pea seeds- controlled by a gene having two allele B & b Starch synthesis effective if homozygote BB & produce large starch grains Homozygote bb-lesser efficiency in starch synthesis & seeds are wrinkled Heterozygote Bb-round seeds, intermediate size .