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Mendel\ S Law
 

Mendel\ S Law

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    Mendel\ S Law Mendel\ S Law Presentation Transcript

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