Mendel\ S Law


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Mendel\ S Law

  1. 1. MENDEL’S LAW
  2. 2. Gregor Mendel 1822-1884 <ul><li>An Austrian scientist =research in a Czechoslovakian monastery. </li></ul><ul><li>Established the basis of modern genetic science. </li></ul><ul><li>Objective = understand how physical traits are passed from a parent to its offspring. </li></ul>                                    
  3. 3. Important concepts <ul><li>Dominance vs Recessiveness </li></ul><ul><li>Principle of Segregation. </li></ul><ul><li>Principle Independent Assortment </li></ul><ul><li>Monohybrid and Dihybrid cross </li></ul>
  4. 4. Important Terms Alleles – Genetic factors that controls a trait, Dominant = ability to mask the expression of a recessive allele (Capital) Recessive = masked by a dominant allele Homozygous - 2 identical alleles (TT, tt) Heterozygous - 2 different alleles (Tt) Genotype - genes of an organism = alleles received during fertilization.   Phenotype = the physical appearance of a trait in an organism . Eg blue eyes, yellow flower
  5. 5. Egs <ul><li>Genotype = genes present in an organism (usually abbreviated as two letters </li></ul><ul><li>TT - Homozygous Dominant (PURE) </li></ul><ul><li>tt -Homozygous Recessive (PURE) </li></ul><ul><li>Tt - Heterozygous </li></ul>
  6. 6. Alleles <ul><li>Alternative forms of the same gene.  </li></ul><ul><li>Eg…. </li></ul><ul><li>Gene for hair texture (curly? Straight?) </li></ul><ul><li>One form of the hair texture gene codes for curly hair.  A different code for of the same gene makes hair straight.  </li></ul><ul><li>= So the gene for hair texture exists as two alleles --- one curly code, and one straight code. </li></ul>
  7. 8. <ul><li>tall stem x short stem = (F1) ALL TALL </li></ul><ul><li>yellow seeds x green seeds = (F1) ALL YELLOW </li></ul><ul><li>round seeds x wrinkled seeds = (F1)ALL ROUND </li></ul>
  8. 9. Monohybrid cross
  9. 10. Punnet square
  10. 14. Conclusion of Exp 1 <ul><li>phenotypes of the offspring resembled only one of the parent plants. </li></ul><ul><li>alleles compete randomly for expression in the offspring depending on Dom/Rec status </li></ul><ul><li>F1 = T x tt = All Tt . the tall factor seems to DOMINATE the short factor&quot;. </li></ul><ul><li>F2 = The trait not shown in the F1 reappeared in the F2 in about 25% of the offspring </li></ul><ul><li>Different offspring of the same parents have different sets of hereditary information </li></ul>
  11. 15. Mendels Law The Law of Segregation <ul><li>pair of alleles of each parent separate and only one allele passes from each parent on to an offspring.  </li></ul><ul><li>Which allele in a parent's pair of alleles is inherited is a matter of chance.  </li></ul><ul><li>segregation of alleles occurs during the process of sex cell formation = MEIOSIS </li></ul>
  12. 16. Mendel's Law of Independent Assortment <ul><li>Alleles for different traits are distributed to sex cells (& offspring) independently of one another. </li></ul><ul><li>Conseq ; new combinations of genes present in neither parent are possible.  </li></ul>
  13. 17. Eg: <ul><li>two different traits: </li></ul><ul><li>(1) seed texture (round or wrinkled) & </li></ul><ul><li>(2) pod color (green or yellow).  </li></ul><ul><li>The different traits do not influence the inheritance of each other.  They are inherited INDEPENDENTLY </li></ul><ul><li>Yellow round, green wrinkled vs Yellow wrinkled, green round </li></ul><ul><li>where &quot;G&quot; = dominant allele for yellow pods &quot;g&quot; = recessive allele for green pods </li></ul><ul><li>“ W&quot; = dominant allele for round seeds “w&quot; = recessive allele for wrinkled seeds . </li></ul>GGWW x ggww vs GGww x ggWW
  14. 19. Dihybrid cross
  15. 20. 9:3:3:1
  16. 21. <ul><li>Eg. 2 </li></ul><ul><li>Purple round, White wrinkled vs </li></ul><ul><li>Purple wrinkled, white round </li></ul><ul><li>Purple dominant (P), </li></ul><ul><li>Round dominant (W), </li></ul><ul><li>Eg. 3 </li></ul><ul><li>Red Tall x White short vs </li></ul><ul><li>Red short, White Tall </li></ul><ul><li>Red dominant (R), </li></ul><ul><li>Tall dominant (T) </li></ul>
  17. 22. <ul><li>PPWW x ppww vs PPww x ppWW </li></ul><ul><li>RRTT x rrtt vs RRtt x rrTT </li></ul>
  18. 23. Summary <ul><li>1 st Law = Dominance </li></ul><ul><li>Parent TT x tt (tall x short) </li></ul><ul><li>Offspring = All tall </li></ul><ul><li>2 nd Law = Segregation </li></ul><ul><li>Parent = Tt x Tt (tall x tall) </li></ul><ul><li>Offspring = 75% tall 25% short </li></ul>
  19. 24. <ul><li>3 rd Law = Independent assortment. </li></ul><ul><li>2 traits </li></ul><ul><li>Parent = GgWw x GgWw </li></ul><ul><li>Offspring </li></ul><ul><li>9/16 yellow pods & round seeds 3/16 green pods & round seeds 3/16 yellow pods & wrinkled seeds 1/16 green pods & wrinkled seeds & </li></ul>