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Introduction to Genetics

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This slideshow describes the findings of Gregor Mendel, an austrian monk who experimented with thousands of pea plants. It also explains how to use punnett squares to find results of crosses between different genotypes.

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Introduction to Genetics

  1. 1. © Fall 2005, Pflugerville ISD, 7th Grade copyright cmassengale 1 Gregor Mendel (1822-1884) The Father of Genetics
  2. 2. © Fall 2005, Pflugerville ISD, 7th Grade Gregor Johann Mendel Austrian monk Studied the inheritance of traits in pea plants Developed the laws of inheritance Mendel's work was not recognized until the turn of the 20th century 2
  3. 3. © Fall 2005, Pflugerville ISD, 7th Grade Gregor Johann Mendel Between 1856 and 1863, Mendel cultivated and tested thousands of pea plants He discovered how heredity works – how organisms transfer their traits to their offspring. copyright cmassengale 3
  4. 4. © Fall 2005, Pflugerville ISD, 7th Grade copyright cmassengale 4 Mendel stated that physical traits are inherited as “particles” Mendel did not know that the “particles” were actually Chromosomes – DNA! Particulate Inheritance
  5. 5. © Fall 2005, Pflugerville ISD, 7th Grade Why peas, Pisum sativum? Why Peas? Produce lots of offspring Grow quickly Can be grown in a small area Can be artificially cross- pollinated copyright cmassengale 5
  6. 6. © Fall 2005, Pflugerville ISD, 7th Grade Mendel and His Peas • Mendel tested 7 traits: 1. Flower color 2. Flower position 3. Seed color 4. Seed shape 5. Pod shape 6. Pod color 7. Plant height http://www.fieldmuseum.org/exhibits/traveling_mendel.htm p173 Life Science Textbook
  7. 7. © Fall 2005, Pflugerville ISD, 7th Grade Mendel and His Peas http://biology.kenyon.edu/courses/biol114/KH_lecture_images/Mendel/Mendel.html What color do you predict? What color do you predict? What color do you predict? What color do you predict? What color do you predict? What color do you predict? What color do you predict? What color do you predict?
  8. 8. © Fall 2005, Pflugerville ISD, 7th Grade Yes, copy the picture.  • The first generation (F1) of plants all had purple flowers. • Where did the white color go?? (Pp) (Pp) (Pp) (Pp) Purple Parent (PP) WhiteParent(pp)
  9. 9. © Fall 2005, Pflugerville ISD, 7th Grade • Mendel crossed his first generation (F1 x F1) purple flowered plants together. • In the second generation (F2) he had 3 purple flowered plants, and 1 white flowered plant. (PP) (Pp) (Pp) (pp) Purple Parent (Pp) PurpleParent(Pp) Yes, copy the picture. 
  10. 10. © Fall 2005, Pflugerville ISD, 7th Grade Mendel and His Peas • Mendel noticed in the first generation, all of the white flowers seemed to disappear. • He called this a recessive trait. • The white color faded away, and was not expressed physically. • But - it showed up in the next generation!
  11. 11. © Fall 2005, Pflugerville ISD, 7th Grade Mendel and His Peas • The purple that overpowered the recessive color was named the dominant trait.
  12. 12. © Fall 2005, Pflugerville ISD, 7th Grade Mendel and His Peas • Mendel found that each plant carried two sets of instructions for each trait (one from the “mom” and one from the “dad”). • These sets of instructions are called alleles.
  13. 13. © Fall 2005, Pflugerville ISD, 7th Grade Below is a pedigree of two peas and their offspring.
  14. 14. © Fall 2005, Pflugerville ISD, 7th Grade Vocabulary - Heredity- the passing of traits from parent to offspring. - Homozygous – both alleles are identical. Also known as True-breeding. Ex: PP or pp - Heterozygous - each allele is different. Also known as hybrids. Ex: Pp
  15. 15. © Fall 2005, Pflugerville ISD, 7th Grade Vocabulary - P generation- the parent generation. - First-generation or F1- the very first set of offspring from two parents - Second-generation or F2 – the offspring of the kids from the F1 generation (grandkids) - Dominant trait- Represented with a capital letter, it overpowers the recessive trait.
  16. 16. © Fall 2005, Pflugerville ISD, 7th Grade Vocabulary Genotype- the genetic code. Ex: Pp Phenotype- the physical appearance. Ex: Purple Flowers Pedigree – your family tree. Incomplete Dominance – a blend of the parents’ phenotypes. Ex: Bb light brown brown white
  17. 17. © Fall 2005, Pflugerville ISD, 7th Grade Vocabulary Codominance – When both phenotypes are visible. Ex: Hair that has both blond strands and brown strands. Karyotype – a chart of all your chromosomes lined up in order. Sex Chromosomes – chromosomes that determine a person’s gender. ex: XX and XY X-linked, or sex-linked inheritance – see p186 in Life Science Book.
  18. 18. © Fall 2005, Pflugerville ISD, 7th Grade Vocabulary -Recessive trait- a trait that shows up only when two recessive alleles for the same characteristic are inherited -Genes- a section of DNA that carries hereditary instructions and is passed from parent to offspring -Alleles- multiple forms of the same gene
  19. 19. © Fall 2005, Pflugerville ISD, 7th Grade Let’s Review 1. If you crossed a true-breeding black rabbit with a true-breeding white rabbit, all of the offspring would be black. Which trait is dominant in rabbits: black fur or white fur? 2. Which trait is recessive?
  20. 20. © Fall 2005, Pflugerville ISD, 7th Grade Answer • The trait for black fur is dominant over the trait for white fur. The white fur trait is recessive. http://www.buckeyevalleyfarms.freeservers.com/photo.html (Bb) (Bb) (Bb) (Bb) Black Rabbit (BB) WhiteRabbit(bb)
  21. 21. © Fall 2005, Pflugerville ISD, 7th Grade Google’s tribute to Mendel July 2011
  22. 22. © Fall 2005, Pflugerville ISD, 7th Grade Science Humor

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