Ch.3,sec.1 mendel's work


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Here is Genetics Chapter 3, Section 1.
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Ch.3,sec.1 mendel's work

  1. 1. MENDEL’S WORKObjectivesWhat were the results of Mendel’s experimentsor crosses?What controls the inheritance of traits inorganisms?
  2. 2. Mendel’s Work Mendel experimented with thousands of Pea plants looking at their different traits to understand the process of heredity. His discoveries form the foundation of genetics. Heredity –the passing of physical characteristics from parents to offspring Trait- each different form of a characteristic Genetics – the study of heredity
  3. 3. Mendel’s Experiments Flowering Plant anatomy Pistil – produces the female sex cells or eggs Stamens – produce pollen which contains the male sex cells or sperm Fertilization is when the egg and sperm join forming a new organism In plants the pollen must reach the pistil for fertilization to occur. This is called pollination
  4. 4. Pollination Pea plants usually self- pollinate. The pollen from their stamens lands on the same plants pistils. Mendel developed a method to cross-pollinate pea plants. He took pollen from one pea plant and brushed it into the pistil of another.
  5. 5. Crossing Pea Plants Mendel crossed plants with contrasting traits Ex. Tall plants with short plants Started with purebred plants a purebred organism is one who is the offspring of many generations of that have the same trait
  6. 6. The F1 Offspring Mendel crossed purebred tall with purebred short Parental (P) generation Tall x short Offspring from the cross are called F1 (filial) All F1 offspring were tall
  7. 7. F2 offspring When F1 were full grown, Mendel allowed them to self-pollinate F were a mix of tall 2 and short ¾ were tall and ¼ were short
  8. 8. Experiments with Other Traits Mendel crossed pea plants with other contrasting traits such as seed shape, seed color, seed coat color, etc. In all crosses the F1 generation had only 1 form of the trait In the F2 generation the “lost” form reappeared in ¼ of the plants.
  9. 9. Dominant and Recessive Alleles  Mendel’s Conclusion  factors control the inheritance of traits in peas.  They exist in pairs  The female parent contributes one factor and the male parent contributes the other factor  One factor in a pair can mask or hide the other
  10. 10. Genes and Alleles Genes – factors that control a trait Alleles – different forms of a gene An organism traits are controlled by the alleles it inherits from its parents. Some alleles are dominant, while others are recessive Dominant allele – trait always shows Recessive allele –trait is hidden whenever dominant allele is present
  11. 11. Alleles in Mendel’s Crosses  Stem Height Cross  P generation tall tall x short short  F1 generation all were tall short- Look tall  F2 generation:  ¼ tall tall - look tall ¼ tall short + ¼ short tall – look tall ¼ short short – look short
  12. 12. Symbols for alleles Letters are used to represent alleles Capital letters are used for dominant alleles Lowercase letters are used for recessive alleles Purebred tall = TT Purebred short = tt Hybrid (one of each) =Tt
  13. 13. Significance of Mendel’s Contribution Before Mendel most people thought that the traits of an individual were a blend of their 2 parents. If they blended the Tt plants should be medium height Mendel found out that traits are determined by individual alleles some of which are dominant and some recessive. Recessive traits may seem to disappear in the offspring only to reappear in the next generation Mendel’s work was not recognized during his lifetime, but was rediscovered in 1900. He is now considered the Father of Genetics.
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