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Mendels Laws of Heredity

Mendels Laws of Heredity. 10.1 Martin aka Tha’ Boss. WHY MENDEL SUCCEEDED?. Heredity: the passing on of characteristics from parents to offspring Traits: the characteristics that are inherited Genetics: the branch of biology that studies heredity. WHY MENDEL SUCCEEDED?.

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Mendels Laws of Heredity

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  1. Mendels Laws of Heredity 10.1Martin aka Tha’ Boss

  2. WHY MENDEL SUCCEEDED? • Heredity: the passing on of characteristics from parents to offspring • Traits: the characteristics that are inherited • Genetics: the branch of biology that studies heredity

  3. WHY MENDEL SUCCEEDED? • A. Mendel Chose his subject carefully • He chose to use garden peas to experiment with • Because they reproduce asexually and have both male and female reproductive organs • Gametes: male and female sex cells • Fertilization: the union of male and female gametes to form a zygote • Zygote develops into a “seed”

  4. WHY MENDEL SUCCEEDED? • A. Mendel Chose his subject carefully • Pollination: when plants transfer pollen grains from the male reproductive organ to the female reproductive organ • Self-pollination: plants usually do this because they have both male and female organs • Let’s take a look at what Mendel did…

  5. WHY MENDEL SUCCEEDED? • Mendel cut away male pollen organs from purple • Mendel got pollen from the white plant and transferred it to the female part of the purple plant • Allowed purple plant to produce “seeds” from this pollination and planted seeds to see what color offspring would be produced.

  6. MENDELS MONOHYBRID CROSS • Hybrid: the offspring of parents that have different forms of a trait • Monohybrid: where two parents only differ by “one” trait

  7. MENDELS MONOHYBRID CROSS • A. The First Generation • Cross Pollination of 2 plants • 1 short, 1 tall • All offspring grew as tall as the tallest parent • The short plant characteristic has been “masked” in this generation • Parent 1 x Parent 2 = F1 Generation

  8. MENDELS MONOHYBRID CROSS • B. The Second Generation • Mendel allowed the F1 offspring to “self pollinate”, then planted the seeds • He noticed now that: • 3/4ths of the plants were tall • 1/4th of the plants were short • 3:1 ratio in the F2 offspring • F1 x F1 = F2

  9. MENDELS MONOHYBRID CROSS • C. The Rule of Unit Factors • Alleles: the different forms that genes can exist in • in other words, each gene is represented by two “letters”. Letters can be capital or lowercase. Each letter is an allele and each gene is represented by 2 letters/alleles • TT, Tt, tt

  10. MENDELS MONOHYBRID CROSS • D. The Rule of Dominance • Dominant: the observed trait in the F1 • Recessive: the trait that disappears in F1, only to return in the F2

  11. MENDELS MONOHYBRID CROSS • E. The Law of Segregation • States that every individual has two alleles of each gene and when gametes are produced, each gamete receives one of these alleles • During fertilization, gametes randomly pair to produce combinations of alleles

  12. MENDELS MONOHYBRID CROSS

  13. PHENOTYPES AND GENOTYPES • Phenotype: the way an organism looks or behaves • Its physical appearance • Tall, or short • Genotype: the allele combination an organism contains • TT, Tt, tt

  14. PHENOTYPES AND GENOTYPES • Genotypes can be described two ways • Homozygous: TT, or tt • Because the alleles are the “same” (homo) • TT is “homozygous dominant” • tt is “homozygous recessive” • Heterozygous: Tt • Because the alleles are different (hetero)

  15. MENDELS DIHYBRID CROSS • A. The First Generation: • Mendel took true breeding round yellow (RRYY) seeds and crossed with true breeding green/wrinkled (rryy) seeds • This produced an F1 that had all round/yellow seeds • This proved that yellow/round were the dominant traits

  16. MENDELS DIHYBRID CROSS • B. The Second Generation: • Mendel allowed a single F1 offspring to self-pollinate • This produced an F2 that had the following phenotypes • 9 – Round/Yellow • 3 – Round/Green • 3 – Wrinkled/Yellow • 1 – Wrinkled Green

  17. MENDELS DIHYBRID CROSS • B. The Second Generation: • The results from Mendel’s F2 experiment led him to his 2nd law regarding genetics • The Law of Independent Assortment

  18. MENDELS DIHYBRID CROSS • C. The Law of Independent Assortment: • States that genes for different traits are inherited independently of each other

  19. PUNNETT SQUARES AND PROBABILITY • We should all be able to complete monohybrid and dihybrid crosses using Punnett Squares at this time • We should be able to describe genotypes and phenotypes of offspring • We should be able to describe ratios among offspring and describe probabilities of phenotypes among offspring • But can we?

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