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Mendelian Genetics


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  • 1. Mendelian Genetics The Basics
  • 2. Gregor Mendel???
    • Known as the Father of Genetics: His experiments with Pea plants from 1856-1863 began our understanding of how traits, things like hair or eye color, height, weight, ect……., were passed down from generation to generation.
    • He came up with the principles of heredity that still hold true today by studying 7 characteristics of peas in his garden.
    • His work started and formed the base of all genetics, a field we learn more about every day.
  • 3.  
  • 4. Introduction
    • Before Mendel it was the Blending Hypothesis which should give rise to a uniform population if true.
    • Mendel started the idea of particulate inheritance, which we use today.
    • Well it all started with just some pea, like Disney all started with a mouse.
    • ???? WHY Peas
      • 1. trait are in 2 very different forms, like flowers are either purple or white and seeds yellow or green and shape round or wrinkled
      • 2. Male and female reproductive parts are contained in the same flower, you can control mating
  • 5. Cont…..
    • 3. It is small and grows easily and quickly producing many offspring. All Good Reasons
  • 6. How did He do it
    • Mendel would cross-pollinate ( hybridize ) two contrasting, true-breeding pea varieties .
      • He got true breeders by allowing self pollination .
      • The true-breeding parents are the P generation and their hybrid offspring are the F 1 generation .
    • Mendel allowed the F 1 hybrids to self-pollinate to produce an F 2 generation. Here he came up with his 2 famous laws of segregation and independent assortment.
  • 7.
    • Mendel reasoned that the heritable factor for white flowers was present in the F1 plants, but it did not affect flower color.
    • This is where dominant and recessive come in.
    • He found a 3:1 ratio in many traits.
  • 8.  
  • 9. The Law of Segregation
    • 1 . different version of genes ( alleles ) account for variations in inherited characters or traits
      • Alleles vary in their nucleotide sequences in genes. Ex Blue and Brown eyes, both eye color genes just different versions
    • 2. For each trait, organisms inherit 2 alleles, one from each parent .
    • 3. If two alleles differ, then one, the dominant allele , is fully expressed while the other, Recessive , is masked or only partially shown
    • 4. The two alleles for each trait segregate during gamete, sex cell, production.
    • Hint: Mitosis and homologous chromosome separation
  • 10. Punnett Square Predictions
  • 11. Genetics Vocabulary
    • organism with two identical alleles for a trait is homozygous. ( TT or tt) Big letters= Dominant small or lower case = recessive.
    • Organisms with two different alleles for a character is heterozygous ( Tt or Pp)
    • description of an organism’s traits is its phenotype Ex) What it looks like, tall, short ,white, black ect….
    • description of its genetic makeup is its genotype. Ex) Homo. D or R, Hetero. D or R.
  • 12.  
  • 13. Test Cross Tales the Tale
  • 14. Law of Independent Assortment
    • Used a dihybrid cross to figure this one out.
    • The Law states that the alleles of different genes separate independently of each other during gamete formation
      • presence of one specific allele for one trait has no impact on the presence of a specific allele for the second trait.
    • So one trait does not influence or control another. Not all dark haired people have dark eyes. Ect…...
    • Show probability just like dice and coin toss
  • 15.  
  • 16. Sound Simple Right????
    • The relationship of genotype to phenotype is rarely simple like in our examples because there are exceptions to all rules.
    • Mendel lucked out in picking peas plants because each trait is controlled by 1 gene, genetically simple. But this is rare….
    • some alleles show incomplete dominance where heterozygotes show a distinct intermediate phenotype, not seen in homozygotes.
    • Snapdragons are good examples
  • 17. Snapdragons
  • 18. Cont…….
    • codominance 2 alleles affect the phenotype in separate, distinguishable ways
      • 2 dominant alleles expressed at the same time.
    • Ex. Is blood type. DRAW. This is also s multiple allele gene have 3 alleles present. A,B,O
    • Fact: Just because an allele is dominant does not make it more prevalent in a population.
      • Ex. Polydactyl is dominant to having the normal 5 fingers and toes but 399 out of 400 have te recessive what we call normal 5 and 5
  • 19.  
  • 20. Cont…..
    • most genes are pleiotropic , affecting more than one phenotypic trait
      • extensive symptoms of sickle-cell anemia are owed to a single gene .
    • epistasis , a gene at one locus, or location, alters the phenotypic expression of a gene at a second locus
      • Ex. Mice and other mammals 1 gene determines if there is pigment in the hair C, there is, c, is not, and another determine color B,black or b, brown. Cc is albino
  • 21. Pleiotropic
  • 22. Epistasis
  • 23. Cont…….
    • polygenic inheritance, the additive effects of 2 or more genes on a single phenotypic trait. It can cause a great range in the phenotypic out come of an individual.
    • Ex. Human skin color controlled by 3 genes
    • AABBCC individual is dark and aabbcc is light
    • crosses between two AaBbCc heterozygote individuals would yield offspring covering a vast range of shades. See pic..
  • 24.  
  • 25.  
  • 26. Phenotype and Environment
    • depends on environment and genes How Much of each???????????????????????????
    • Ex. nutrition influences height and weight, exercise alters build, sun-tanning darkens the skin, and experience improves performance on intelligence tests
    • Ex . Hydrangea- Acid soil = blue flower and base= pink. Genes are the same for both. Ex. Artic Fox turns brown in summer and white in winter so does snow shoe hair and grouse. Ex . Fur color in Siamese cats influenced by temp. and so is Crotalus horridius , Sex in many animals reptiles esp. is determined by temp. Ex. Identical twin diff. Use human examples , personality and height ect….
  • 27. References
    • Jack Brown M.S. Biology
    • Starr and Taggart: The Unity and Diversity of Life 10th edition : 2004: Thomson Brookes/Cole
    • Campbell and Reece: Biology 6th edition . Pg 1-23: 2002: Benjamin Cummings.
    • Microsoft Encarta Encyclopedia 2004
    • Raven and Johnson: Holt Biology : 2004: Holt, Rinehart and Winston.