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Mendelian Genetics

Mendelian Genetics. Commitment . What is something you are really committed to (such as a goal, a hobby, a sport or maybe some other cause)? . Inheritance. What was the first explanation for resemblances between parent and offspring?

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Mendelian Genetics

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  1. Mendelian Genetics

  2. Commitment What is something you are really committed to (such as a goal, a hobby, a sport or maybe some other cause)?

  3. Inheritance • What was the first explanation for resemblances between parent and offspring? • Theory of blended inheritance-people reasoned that each parent contributed factors that were blended in their offspring.

  4. Mendel’s Experiment Purpose: Believed that there was a mathematical explanation for inheritance (passing characteristics from parents to offspring). • He studied peas because… • He had access to varieties with many different traits. • Peas also reproduce by self-pollination (simple and quick) • Small • Easy to grow • Easy to reproduce in large amounts • Mature quickly

  5. Step 1: Purebreds • Grew purebredpea plants. • Purebred- produces the same trait in its offspring for generations. • Accomplished by self-pollination • Allowed plants with each trait to self pollinate for several generations

  6. He snipped the stamen to prevent self-pollination and covered each flower with a bag cloth.

  7. Materials • Mendel grew and selected seven true breeding varieties of peas- each had a peculiar trait • Seed shape: round vs. wrinkled • Seed color: yellow vs. green • Flower color: purple vs. white • Pod shape: smooth vs. constricted • Pod color: green vs. yellow • Flower position: axial vs. terminal • Stem length: tall vs. short

  8. Axial Tall Short Terminal Green Round Wrinkled Yellow Gray White Yellow Smooth Constricted Green

  9. Step 2: Cross Fertilization • After many generations, purebreds of the same trait were cross- pollinated and the first generation of offspring resulted • Transferred pollen using a paintbrush • Snipped the stamens to prevent self-pollination

  10. P= purebred/ parent generation F1= First Generation Offspring

  11. Results from Step 2 • Offspring only showed one of the parent’s traits • Mendel thought that traits disappeared in the first generation of offspring. • He needed to know if the other trait had disappeared completely … led to step 3

  12. Step 3 Mendel let the offspring (F1 generation) self-pollinate and produce a second generation of plants (F2 Offspring).

  13. Results from Step 3 • Mendel discovered that when the offspring self-pollinated, the lost trait reappeared. • Mendel concluded that there are 2 building blocks necessary to create a trait- he called these genes.

  14. Mendel’s Results 3:1 Ratio

  15. The 3rd Experiment… Closure • Rewind to Experiment 1: • When Mendel crossed the purple and white purebreds, the purple plant could only give purple genes & the white plant could only give white genes • Mendel called these variations of genes alleles • Rewind to Experiment 2: • When the purebreds were crossed, each offspring (F1 plant) had one purple and one white allele • All the F1 plants were purple b/c the purple allele hid the white allele from view • Dominant allele- name given to the allele that masks other alleles • Recessive allele - name given to the allele that was hidden • Closure to Experiment 3: • When the F1 plant was self-fertilized, the dominant and recessive traits were both observed

  16. Bell Work Describe Mendel’s First, Second and Third Step in his experiment with pea plants.

  17. Conclusion • Mendel discovered the Principle of dominance. • The Principle of Dominance states that the dominant allele (variation of a gene) will prevent the recessive allele from showing up in the offspring. • Discovered in the first cross of purebreds.

  18. Conclusion Cont… • Law of Segregation: states that alleles separate when passed on from parents to offspring. • Only one allele, from a gene (for a specific trait) is passed from the parent to the offspring. •  Alleles for a trait are “recombined” at fertilization, producing the genetic composition (genotype) for the observable traits (phenotype) of the offspring.

  19. Principle of Segregation • Segregation of alleles

  20. Conclusion Cont… • Principle of Independent Assortment- Mendel discovered that plants could have many combinations of characteristics • Ie. If a pea plant is tall, it can have green seeds or yellow seeds that are either smooth or wrinkled. • Each trait is independent of each other

  21. Important Vocabulary: • Trait- A genetically determined characteristic • Chromosome:A linear strand of DNA harboring many genes. • Gene:A DNA segment that gives instructions for making protein • Allele:An alternate form of a gene • There are only two alleles for each gene: one allele comes from the mother and one from the father • Locus (Loci)- specific place where a gene occurs on a chromosome

  22. Important Vocabulary Loci with Different alleles Loci with identical alleles • Homozygous- organisms w/ two identical alleles for a particular gene (aka purebred) • i.e. Tall & short pea plants…TT and tt • Heterozygous-organisms w/ two different alleles for the same gene (aka hybrid) • i.e.Tall and short pea plants… Tt

  23. Important Vocab. Phenotype- observable physical characteristics (Tall or short) Genotype- genetic composition of alleles (TT, Tt, tt)

  24. The 1st Cross w/ Toothpicks! • What does each popsicle stick represent? • Chromosome…so when we put two together they represent a homologous (paired) chromosome • What do the colored spots on the toothpicks represent? • Genes (specifically alleles) found on the chromosome • Even though they carry the same gene, they can carry different alleles for that gene

  25. Genetic Cross w/ Toothpicks • Use your diagram and your toothpick chromosomes to model pea plant reproduction. • Show the cross that gave Mendel purebreds • Show the purebred cross that resulted in the F1 generation • Show the F1 cross and the F2 results

  26. Easier way=Punnett Square • Punnett Square- graphic organizer that shows the gene combinations that are possible for an offspring to inherit when two individuals mate.

  27. Depending on the egg that is fertilized, the mother can give a dominant allele found on one chromosome or a recessive allele found on the other. Depending on the sperm, the father can give a dominant allele found on one chromosome or a recessive allele found on the other. Punnett Squares… show the Law of Segregation

  28. Monohybrid Cross Genotypic Ratio: 1 PP:2 Pp:1 pp Genotypic Ratio: 25% PP 50% Pp 25% pp Phenotypic Ratio: 75% Purple 25% White Phenotypic Ratio: 3 Purple:1 White

  29. Monohybrid Cross • Step One: Figure out the genotypes of the parents. • What alleles (different versions of a gene) could they pass to their offspring • Step Two: Set up a Punnett Square for your mating. • Step Three: Figure out what kinds of gametes the parents can produce. • Determine all the possible ways that the male sperm can combine with the female eggs • Step Four: Fill in the possible genotypes of the offspring inside the table

  30. Pea Plant Traits Seed Shape… Round (R) or Wrinkled (r) Seed color…. Yellow (Y) or Green (y) Pod shape… Smooth (S) or Wrinkled (s) Pod color…. Green (G) or Yellow (g) Seed Coat Color… Gray (G) or White (g) Flower Position… Axial (A) or Terminal (a) Plant Height… Tall (T) or Short (t) Flower color… Purple (P) or white (p)

  31. Let’s Do Lunch 1st Date- front page 2nd Date- 1-2 on the back 3rd Date- 3-5 on the back

  32. Bell Work Determine the genotype and phenotype ratios of each cross!

  33. Dihybrid Cross

  34. Dihybrid Cross TtGg TtGg

  35. TG Tg tG tg TG Tg tG tg

  36. TG Tg tG tg TG Tg tG tg Genotypes: TTGG: TtGG: ttGG TTGg: TtGg: ttGg: TTgg: Ttgg: ttgg: Phenotypes: Tall and Green- Tall and Yellow- Small and Green- Small and Yellow-

  37. Your Turn!

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