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Hour 1


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Hour 1

  2. 2. Concept review… Genetic inheritance Terms & concepts Mendel’s experiment Pisum sativum – garden pea Monohybrid crosses Dihybrid crosses Law of segregation Law of independent assortment Deviation from Mendel’s Law <ul><li>Codominance </li></ul><ul><li>Incomplete dominance </li></ul><ul><li>Multiple allele </li></ul><ul><li>Polygene </li></ul><ul><li>Lethal allele </li></ul><ul><li>Linked gene </li></ul>Genetic mapping Pedigree analysis
  3. 3. Important terms… allele genes locus genotype phenotype dominant recessive homozygous heterozygous true-breed
  4. 4. OBJECTIVE <ul><li>Define terminologies used in genetic inheritance. </li></ul><ul><li>Describe the characteristics of Mendel’s pea plants. </li></ul>
  5. 5. Terms used in genetic inheritance <ul><li>Alleles: </li></ul><ul><ul><li>all the different molecular forms of the same genes </li></ul></ul><ul><li>Genes: </li></ul><ul><ul><li>units of information about specific traits and they are passed from parents to offspring/ small section of DNA that codes for a particular protein. Cells with a diploid chromosome number (2n) have pairs of genes, on pairs of homologous chromosomes. </li></ul></ul>
  6. 6. <ul><li>Locus </li></ul><ul><li>Each gene has a specific location locus on a chromosome . </li></ul>P Q p q
  7. 7. There are two loci , one is for flower color and the other is for stem length
  8. 8. <ul><li>Two terms help keep the distinction clear between genes and the traits they specify. </li></ul><ul><ul><li>Genotype </li></ul></ul><ul><ul><li>Particular genes and individual carries / </li></ul></ul><ul><ul><li>the genes that an organism inherits from its mother and father. </li></ul></ul><ul><ul><li>Phenotype </li></ul></ul><ul><ul><li>An individual’s observable traits/ the protein </li></ul></ul><ul><ul><li>used by these genes that determine the organism’s </li></ul></ul><ul><ul><li>physical characteristic. </li></ul></ul><ul><li>Eg: </li></ul><ul><li>Phenotype : tall </li></ul><ul><li> Genotype : TT @ Tt </li></ul>
  9. 9. <ul><ul><li>An allele is said to be dominant when its effect on a trait masks that of any recessive allele paired with it. We used capital letters for dominant alleles and lowercase letters for the recessive one. Example, A and a. </li></ul></ul><ul><ul><li>So, the homozygous dominant has a pair of dominant alleles (AA), homozygous recessive has a pair of recessive alleles (aa) and heterozygous has a pair of non-identical allele (Aa). </li></ul></ul>
  10. 10. <ul><li>True-breed @ pure-breed </li></ul>Organisms that are homozygous for any given genotype and therefore pass it on to all their progeny in a cross with a similar homozygote
  11. 11. <ul><li>P : parental generation </li></ul><ul><li>F1 : first-generation offspring </li></ul><ul><li>F2 : second-generation offspring </li></ul>
  12. 12. TYPES OF CROSSES <ul><ul><li>Test cross </li></ul></ul><ul><ul><li>A cross between a recessive homozygous and an </li></ul></ul><ul><ul><li>organism of dominant phenotype , but unknown </li></ul></ul><ul><ul><li>genotype. </li></ul></ul><ul><ul><li>If an organism displays a dominant characteristic, it may possess 2 dominant alleles (homologous) or a dominant and recessive allele for that characteristic (heterozygous) </li></ul></ul><ul><ul><li>To find out which in the case, the organism is crossed with one displaying the recessive characteristic. </li></ul></ul><ul><ul><li>If all the offspring show the dominant characteristic then the organism is homozygous, but if half show the recessive characteristic, then the organism is heterozygous. </li></ul></ul>
  13. 13. <ul><li>Self cross </li></ul><ul><ul><li>Male and female from the same plants /generation </li></ul></ul><ul><li>Back cross </li></ul><ul><ul><li>A mating between individuals of the parental generation (P) and the first generation (F1) in order to identify hidden recessive alleles. </li></ul></ul>
  14. 14. <ul><li>Reciprocal cross </li></ul><ul><li>A cross reversing the roles of males and females to confirm the results obtained from an earlier cross. </li></ul><ul><ul><li>For example, if a pollen (male) from tall plants in transferred to the stigma (female) of dwarf plants in one cross, the reciprocal cross would use the pollen of dwarf plants to pollinate the stigmas of tall plants. </li></ul></ul>
  15. 15. P : X b X b x X B Y color blind normal G : X b X b X B Y F1 : X B X b X B X b X b Y X b Y EARLIER CROSS B – normal b – color blind normal female Color blind male Phenotype ratio : 1 normal : 1 color blind
  16. 16. P : X B X B x X b Y normal color blind G : X B X B X b Y F1 : X B X b X B X b X B Y X B Y RECIPROCAL CROSS Female carrier Normal male Phenotypic ratio : All normal
  17. 17. Mendel’s Experiment <ul><li>Gregor Mendel studied the inheritance of </li></ul><ul><li>characteristics in garden peas ( Pisum sativum ). </li></ul><ul><li>He chose peas because : </li></ul><ul><li>they were easy to grow </li></ul><ul><li>they had a short life cycle </li></ul><ul><li>their pollination could be controlled </li></ul><ul><li>they have easily observable characteristics . </li></ul>
  18. 18. <ul><li>He studied 7 characteristics, each of which </li></ul><ul><li>has two contrasting alternatives. </li></ul><ul><li>seed shape : round / wrinkled </li></ul><ul><li>seed color : yellow / green </li></ul><ul><li>pod shape : inflated / constricted </li></ul><ul><li>pod color : yellow / green </li></ul><ul><li>flower color : purple / white </li></ul><ul><li>flower position : axial / terminal </li></ul><ul><li>plant height : tall / dwarf </li></ul>
  19. 19. Page 250
  20. 20. Mendel’s Experimental Result <ul><li>Character Dominant vs F 2 Ratio </li></ul><ul><li>recessive </li></ul><ul><li>Seed shape R x r 5474 : 1850 2.96 :1 </li></ul><ul><li>Seed color Y x y 6022 : 2001 3.01 :1 </li></ul><ul><li>Flower color P x p 705:224 3.15 : 1 </li></ul><ul><li>Pod shape I x i 882:299 2.95 : 1 </li></ul><ul><li>Pod color G x g 428:152 2.82 : 1 </li></ul><ul><li>Flower position A x a 651:207 3.14 : 1 </li></ul><ul><li>Plant height T x t 787:277 2.84 : 1 </li></ul>
  21. 21. <ul><li>It shows 7 characters studied in garden pea crosses and the data obtained. </li></ul><ul><li>F 2 generation showed close to 3:1 ratio of characteristics. </li></ul>