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Genetics and inheritance


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Genetics and inheritance

  1. 1. Genetics• What is genetics? study of inherited traits - “heredity”• What is heredity? passing of traits from parents to offspring (children)• What is a trait? feature an organism can pass on to offspring ex) hair color, eye color, etc
  2. 2. Early Ideas - Heredity• Originally believed… child’s traits were result of “blending between parent’s traits”• Gregor Mendel decided to test this idea• He knew nothing about DNA
  3. 3. • Genes!• Genes are… segments DNA on chromosome code for a trait by the production of a protein• There are several genes on each chromosome.
  4. 4. Mendel’s Pea PlantsWhy did Mendel usepea plants?1) Severalcontrasting traits2) Understoodmethod reproduction
  5. 5. Mendel’s Experiments• The 1st thing Mendel did was cross purebred plants…• Purebred- produce young with same trait generation after generation• What will happen if cross plants with different forms of a trait?• Ex) trait – seed shape forms – round or wrinkled seed shape
  6. 6. Mendel’s Experiments con’t• Parental generation (P) “original group”• First filial generation (F1) offspring of the parental cross• ALL offspring resulted were ROUND
  7. 7. Mendel’s Conclusion• “NO blending- no ½ round ½ wrinkled seeds”
  8. 8. We NOW know why…• Many traits have 2 alleles• Allele- 2 contrasting forms of a trait ex) gene on chromosome for trait–seed shape 2 forms - round allele or wrinkled allele• Principle of Dominance- one allele appears and causes contrasting allele NOT to appear• dominant allele - hides the other allele; capital letter• recessive allele- form often NOT expressed,
  9. 9. Mendel’s 2 Experiment nd• The next question Mendel wanted to answer was: Why didn’t any of the recessive characteristics like (wrinkled) show up in the F1 generation? • To answer this question Mendel extended his experiment and allowed F1 to reproduce…
  10. 10. Mendel’s Results• Second filial generation (F2)- offspring of F1• Some offspring showed recessive trait, some the dominant trait 3:1 ratio (round:wrinkled)
  11. 11. Mendel’s Conclusion• Why did the recessive trait disappear in the F1 and then reappear in some of the F2?• The dominant allele hides the recessive allele in the F1• Since the recessive allele reappeared in the F2 it must have “separated” from the dominant allele• Law of Segregation- when gametes form alleles for a trait are separated (each parent gives one allele to offspring)
  12. 12. Mendel’s Results Summarized• Every trait is controlled by at least 2 different factors (1 gene / 2 allele) Use letters to represent contrasting forms (alleles) for a trait Example: Trait: Seed Color (letter Y) Y = yellow (dominant allele) y = green (recessive allele)• Alleles occur in pairs (1 mom/1 dad)• YY homozygous dominant – 2 same letter - capital Yy heterozygous – 2 different letters yy homozygous recessive - 2 same letter - lowercase• Phenotype - outward appearance/physical characteristic• Genotype - genetic makeup “letters”