Ch 11 intro mendelian genetics sp11

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Ch 11 intro mendelian genetics sp11

  1. 1. Mendelian Genetics<br />Chapter 11<br />
  2. 2. Gregor Mendel – “Father of Genetics”, first Geneticist, one of the most important scientists in history<br />Austrian Monk (1822-1884<br />Worked with ordinary garden peas<br />Used science and math skills learned from University.<br />
  3. 3. Genetics – the scientific study of heredity<br />
  4. 4. Mendel’s Peas – background information<br /><ul><li>The anther (♂, male) produces sperm
  5. 5. The ovary (♀, female) produces eggs
  6. 6. Sperm + Eggs: FERTILIZATION
  7. 7. The peas Mendel started with were TRUE-BREEDING.</li></ul>Gametes<br />
  8. 8. More Peas<br />True-breeding: parents always have offspring identical to themselves when allowed to self-pollinate. (Is self-pollination sexual or asexual reproduction?)<br />For example: Plants with white flowers produce only offspring with white flowers.<br />
  9. 9. Important terms<br />Trait = specific observable characteristic<br />Mendel produced hybrids<br />Hybrid<br />The offspring produced by parents with differing forms of a trait.<br />Some genetics notation<br />Parent generation = P<br />F1 = first generation of offspring from a cross, (F2= second generation, etc.)<br />Contrast with true-breeding<br />
  10. 10. Mendel’s crosses…results<br />Seed Shape<br />Flower Position<br />Seed Coat<br />Color<br />Seed Color<br />Pod Color<br />Plant Height<br />Pod<br />Shape<br />Round<br />Yellow<br />Gray<br />Smooth<br />Green<br />Axial<br />Tall<br />Wrinkled<br />Green<br />White<br />Constricted<br />Yellow<br />Terminal<br />Short<br />Round<br />Yellow<br />Gray<br />Smooth<br />Green<br />Axial<br />Tall<br />
  11. 11. Mendel’s crosses…results<br />Seed Shape<br />Flower Position<br />Seed Coat<br />Color<br />Seed Color<br />Pod Color<br />Plant Height<br />Pod<br />Shape<br />Round<br />Yellow<br />Gray<br />Smooth<br />Green<br />Axial<br />Tall<br />Wrinkled<br />Green<br />White<br />Constricted<br />Yellow<br />Terminal<br />Short<br />Round<br />Yellow<br />Gray<br />Smooth<br />Green<br />Axial<br />Tall<br />
  12. 12. Genes<br />Mendel eventually concluded that traits are passed from one generation to the next.<br />Today, we know that…<br />Traits are determined by GENES<br />Chemical factors that determine a trait. <br />Consist of DNA sequences<br />Alleles - Different forms of a gene<br />Ex. Eye color is a trait, you could have 2 blue eye color alleles, you could have 2 brown eye color alleles, you could have one of each.<br />You get one allele from each parent for each trait.<br />Mendel did not know anything about genes, DNA, chromosomes, meiosis, etc.<br />
  13. 13. Dominant and Recessive Genes<br />Principle of Dominance: Some alleles are dominant and others are recessive.<br />Dominant: An allele that is expressed (visible) whether it is the only version of the gene present or when in combination with a recessive allele.<br />Recessive: An allele ONLY expressed when dominant allele is NOT present<br />
  14. 14. Symbols to represent Dominant Genes<br />If the symbol “T” represents the dominant allele (or form of the gene), then…<br />it doesn’t matter whether both of the alleles an individual has are dominant (TT) or…<br />there is just one copy of the dominant allele (Tt).<br />Either way, the individual looks the same (it has the dominant trait).<br />
  15. 15. Symbols to represent Recessive Genes<br />If the symbol “t” represents the recessive allele (or form of the gene), then…<br />both of the alleles an individual has must be recessive (tt) to have the recessive trait.<br />The presence of one dominant allele (T) hides the recessive allele (t) when there is one of each (Tt).<br />
  16. 16. Important vocabulary<br />Homozygous <br />two identical alleles for a trait. (ex. SS or ss)<br />TRUE-BREEDING for a trait<br />Heterozygous<br />two DIFFERENT alleles for a trait (ex. Ss)<br />HYBRID for a trait<br />Phenotype<br />physical characteristics, appearance<br />Genotype<br />genetic make up, the information in DNA<br />
  17. 17. End part one<br />
  18. 18. Mendelian Genetics<br />Chapter 11<br />
  19. 19. Segregation<br />SEGREGATION<br />Separation of alleles during gamete formation (meiosis)<br />Gamete<br />Sex cells <br />carry a single copy of each gene (ex. The allele for short OR the allele for tall, not both)<br />
  20. 20. Genetics and Probability <br />Probability<br />likelihood that a particular event will occur.<br />For example: What is the probability of rain tomorrow? <br />How likely is it that a flipped penny will land heads-up? Tails-up?<br />Probability is used to predict the outcomes of genetic crosses.<br />
  21. 21. Steps to a setting up a Punnett Square <br />Identify parental genotypes for the cross (ex. TT, tt, Tt)<br />Draw the Punnett Square--a grid with each set of parental alleles on its own side.<br />Separate the alleles (why?)<br />Match alleles from rows and columns to make offspring genotypes.<br />Identify the kinds (and their numbers) of offspring you have.<br />Gametes (sperm or eggs) are haploid (one set of chromosomes)<br />
  22. 22. Steps to a setting up a Punnett Square: An Example<br />Both parents are heterozygous for plant height, with tall being dominant to short.<br />Describe their offspring.<br />
  23. 23. Probability<br />Look at the cross we just did. <br />How many offspring have two alleles for tallness (TT)?<br />Two for shortness (tt)?<br />Both (Tt)?<br />
  24. 24. Probabilities<br />¼ or 25% have two alleles for tallness.<br />¼ or 25% have two alleles for shortness.<br />½ or 50% have one allele for tallness and one for shortness.<br />We write this in terms of a ratio 1TT: 2Tt: 1tt<br />This ratio of allele combination types is called the genotypic ratio.<br />
  25. 25. Probabilities<br />How many plants will be tall and how many will be short?<br />We also write this in terms of a ratio (3 tall: 1 short).<br />This ratio of physical types is called the phenotypic ratio.<br />
  26. 26. 3 tall (75%), 1 short (25%)expressed as a ratio, 3:1<br />Why?<br />1 homozygous for tallness (TT) and the<br />2 heterozygous plants (Tt)<br />You lump these together because you cannot tell any of these offspring apart for this trait—TT offspring look exactly like Tt offspring.<br />1 homozygous recessive (tt)<br />
  27. 27. This is exactly what Gregor Mendel did in his pea experiments.<br />
  28. 28. A brief explanation…<br />All of the reproduction we will be discussing regarding Mendel’s garden peas will be sexual reproduction (a new organism formed by the joining together of a male and a female gamete).<br />However, pay close attention to who the parents are — sometimes there is a cross between two different parents (usually with contrasting forms of some trait, like flower color or height). Other times, the peas are allowed to do what comes naturally to peas—self-pollination (the same plant fertilizes itself). <br />
  29. 29. Sexual Reproduction in Plants<br />Male (♂) sexual organs<br />Female (♀) sexual organs<br />
  30. 30. Cross-pollination – either by wind, insect or geneticist<br />Pollen (containing male gametes)<br />
  31. 31. Self-pollination<br />Convenient, but boring<br />
  32. 32. Mendel’s Monohybrid cross<br />Mendel’s first crosses<br />The parent generation (P) is a combination of two different pure-breeding types<br />The first generation (F1) produced only TALL plants<br />The second generation (F2 ) produced tall and short plants<br />Tall allele/Tall allele<br />TT<br />short allele/short allele<br />tt<br />
  33. 33. Predictions<br />Mendel found that the approximately three dominant to one recessive ratios showed up consistently.<br />Probabilities predict average outcomes for a LARGE number of events, not exact outcomes. <br />Flip a coin twice<br />Heads once, tails once<br />Heads twice<br />Tails twice<br />Flip a coin many times, likely to get very close to a 50:50 ratio<br />
  34. 34. Predicting Genetics<br />Genetics is similar<br />Larger numbers result in closer to expected values.<br />This explains why humans don’t always have the same number of male children and female children despite the fact that the odds of any one child’s gender is 50% female, 50% male.<br />
  35. 35. Mendel’s Principle<br />Independent Assortment<br />Genes for different traits segregate independently during gamete formation<br />Accounts for much of the genetic variation in living things<br />Usually, all combinations of traits are possible, <br />ex. Tall round seeds, purple flowers<br /> Short round seeds, white flowers<br /> Short wrinkled seeds purple flowers<br /> Tall wrinkled seeds white flowers<br />Etc. <br />
  36. 36. Summary of Mendel’s Principles <br />Genes determine inheritance. Genes are passed from parent to offspring.<br />Some genes may be dominant and others recessive<br />Adults (sexually reproducing) have two copies of each gene—one from each parent. They segregate during gamete formation.<br />Alleles for different traits assort independently (Independent Assortment)<br />

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