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Mendelian Genetics

Mendelian Genetics. Early Ideas about Inheritance. ( (384 BC - 1800s) – Hippocrates and Aristotle - Eggs and sperm formed from particles in the body called pangene s, which come together from all parts of the body, mainly the blood.

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Mendelian Genetics

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  1. Mendelian Genetics

  2. Early Ideas about Inheritance ( (384 BC - 1800s) – Hippocrates and Aristotle- Eggs and sperm formed from particles in the body called pangenes, which come together from all parts of the body, mainly the blood. • oHomunculus (little person in sperm) Debate for over 250 years! idea from ancient Greeks; egg is a passive growth medium, sperm brings little miniature being that begins growth in egg. • o(1600s) - Leeuewenhoek- sperm was discovered by Leeuwenhoek: All inherited traits come from the father; the homunculus came from father ;the mother is only the incubator of the offspring. • o(1600s) - Regnier de Graaf–thought homunculus was in the egg: All inherited traits come from the mother; the sperm is only the catalyst that stimulates the growth of the egg. • o(early 1800s) - Blending Theory - Traits of the parents are blended irreversibly, much as paints do, to form the traits of the offspring. • o(mid 1800s) - Darwin & Lamarck - Changes that occur in various parts of the body during a person's life could be passed on to the next generation.

  3. Gregor Mendel • Austrian monk in mid 1800’s. • “Father of Genetics.” • Used pea plants to study heredity. • His principles of heredity still used in modern genetics!!

  4. Heredity=  passing of traits from parent to offspring)

  5. Before Mendel’s experiments, people thought offspring were a blend of their parents. EX: tall plant X with short plant would produce a medium sized plant. Mendel proved this to be untrue, concluding that each trait has 2 “heritable factors” for each trait – one from each parent.

  6. We now know that these factors are genes and that they are located on chromosomes. • alleles are alternate forms of a gene • like purple and white flowering pea plants

  7. Alleles • They arelocated on different copies of a chromosome—one inherited from the female parent and one from the male parent.

  8. Principle/Law of Unit characters • Unit characters= • (independent characters) • EX: height, color, shape etc. are inherited separately

  9. Mendel’s Experiments • Large groups of pea plants. • Expressed results using math. • Began with “pure” pea plants. • Used self-pollination and later cross-pollination. • Controlled the crosses.

  10. Compare Self pollination & Cross pollination

  11. P generation F1generation • Parent plants = P1 • First Offspring = F1 • If F1 were crossed = F2 • Mendel studied 7 pea traits (characteristics) to discover patterns of heredity. Fertilization among F1 plants(F1 x F1) F2generation 1/4 of plantshave white flowers 3/4 of plantshave purple flowers

  12. Flower position = Axial or Terminal Plant height = Tall or Short Pod color = Green or Yellow Pod appearance = Inflated or Constricted Seed color =Yellow or Green Seed appearance = Round or Wrinkled Flower color = Purple or White Seven Traits of Peas:

  13. For example…

  14. What he learned… • When he cross-pollinated tall and short plants, he always got tall plants!! • The short “factor” seemed to be hidden. • He decided the tall “factor” must be dominantover the recessive short “factor.” T T t t T t T t

  15. Dominance!

  16. This is the Principle of Dominance and Recessiveness!! P generation F1 F2

  17. Then, the second generation… • Tall F1 plants were crossed. • A 3:1 mix of tall to short plants made up the F2 generation. • How did the short “factor” reappear?? • There must be 2 “factors”, each separate from the other! • (factors are genes – there are 2 of each: one from Mom, one from Dad.

  18. BB bb Bb • Genotype = what the genes are!!! Ex: Bb or BB or bb • Phenotype = what it looks like!!! Ex: brown or blonde • Homozygous = two of the same!!! Ex: RR or rr • Heterozygous = two different!!! Ex: Rr

  19. F1 Crossed with F1:This is a Monohybrid Cross

  20. Punnett square Punnett Square – predicts outcomes - shows all possible outcomes alleles of 1 parent alleles of other parent

  21. This is the Principle of Segregation!! Two chromosomes in a pair carry the two separate genes!

  22. To test his theory…

  23. To make sure…

  24. What about 2 different traits? • Plants with two distinct traits were crossed. (tall with round seeds vs. short with wrinkled) • The 2 acted separately! (Could get tall with wrinkled seed.)

  25. A Dihybrid Cross…

  26. F1 Generation:

  27. Example:

  28. The 9:3:3:1 Ratio!! Thanks to: www.blc.arizona.edu/courses/181gh/rick/genetics2/dihybrid.html

  29. RRYY rryy ry Gametes RY RrYy Eggs 1/4 RY 1/4 RY 1/4 rY 1/4 rY RRYY 1/4 Ry 1/4 Ry RrYY RrYY 1/4 ry 1/4 ry RRYy rrYY RrYy Yellow round RrYy RrYy RrYy RrYy 9/16 Green round rrYy RRyy rrYy 3/16 Yellow wrinkled Rryy Rryy 3/16 Yellow wrinkled rryy 1/16 This is the Principle of Independent Assortment!!

  30. The four principles: • Principle of Unit Characters • Principle of Dominance and Recessiveness • Principle of Segregation • Principle of Independent Assortment

  31. And knowing those is the backbone of modern genetics!

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