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Mendel’s Experiments

Mendel’s Experiments . Part II: Law of Segregation Biology 12. Joke of the day:. Review: experiment 1. Mendel found that 100% percent of the F 1 ’s had purple flowers

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Mendel’s Experiments

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  1. Mendel’s Experiments Part II: Law of Segregation Biology 12

  2. Joke of the day:

  3. Review: experiment 1 • Mendel found that 100% percent of the F1’s had purple flowers • Mendel found that one trait always appeared and the other trait vanish? The trait that appeared = dominant and he trait that disappeared = recessive

  4. Mendel’s Second Experiment • Crossed the F1 generation with itself to produce the F2 generation

  5. What happened? • Mendel found that the recessive trait appeared again • Mendel repeated this experiment many times and each time found that the F2 generation had the dominant trait 75% of the time and the recessive trait 25% of the time • This 3:1 ratio is known as the Mendelian ratio

  6. Again: tall and short…

  7. Again: yellow and green….

  8. Why did this happen? • Mendel realized that there must be two sets of instructions for each characteristic and that each parent would donate one set of instructions to offspring • Now we know that the sets of instructions are genes and that a fertilized egg would have two forms of the same gene for every characteristics and we call these two forms alleles.

  9. Why did this happen? • During meiosis the alleles (one on each chromosome) for a trait separate into different gametes • Because one chromosomes of each pair goes to a different gamete • Offspring inherit one allele from sperm and one from egg • If the dominant allele is present it will be expressed (PP and Pp) • The recessive allele will only be expressed if both alleles are recessive (pp)

  10. 2. Law of Segregation • The two alleles of a gene pair are separated from each other during gamete formation

  11. Mendel’s other principle: • 3. Principle of Independent Assortment • When more then one trait is studied in the same cross, the genes for each trait sort into gametes independently of the genes of the other traits

  12. But today….. • We now know that Mendel’s principles of Dominance and Independent Assortment are not always true! • Some genes have incomplete dominance. • Some genes are linked on the same chromosomes so they do not sort independently.

  13. To do: • Complete Personal Profile and Questions

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