Geneticsnotes ch9 bio


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Geneticsnotes ch9 bio

  2. 2. I. The History of GeneticsGenetics = field of biology devoted tounderstanding how traits are passed fromparent to offspring
  3. 3. Heredity= the transmission of characteristics fromparent to offspring
  4. 4. Mendel’s Experiments Gregor Mendel – the father of genetics
  5. 5. Mendel’s ExperimentsContinued…Mendel’s Experiments (1856 – 1863)  Observed characteristics of pea plants (7) over a long period of time (28,000 plants over 8 years!)  Initial observation = when he planted purple pea plants some white pea plants grew
  6. 6. Mendel’s Methods:1. grew pure purple and pure white plants for several generations (P1 generation = parent generation)
  7. 7. Mendel’s Methods continued…2. cut off anthers from purple plants (malepart)
  8. 8. Mendel’s Methods continued…3. cross-pollinated purple and white pure strains 4. F1 generation grew (first filial generation) and he counted the number of purple and white plants 5. all F1 plants were purple
  9. 9. Mendel’s Methods continued… 6. allowed self-pollination of F1 generation, producing the F2 generation75% were purple 7.25% were white
  10. 10. Mendel’s Conclusions: 1. something within the pea plantscontrolled the characteristics he observed = “factors” 2. each trait was inherited by a separate“factor”, since he observed 2 forms of each trait he hypothesized each characteristic came in pairs
  11. 11.  Mendel’s traits were carried by “factors” in each plant Each trait had 2 possible “factors” (pairs)
  12. 12. Mendel’s Conclusionscontinued… 3. since 1 trait completely disappeared in the F1 generation, but appeared in a 3:1ratio in the F2 generation, he hypothesized that one of these “factors” was dominant and one was recessive = Rule of Dominance
  13. 13. Laws that Evolved from Mendel’sWork The Law of Segregation = The two alleles (“factors”) for each trait must separate during gamete formation (meiosis). There will only be one allele for a trait in each
  14. 14. Laws the Evolved from MendelThe Law of Independent Assortment =the alleles for each trait must behaveindependently of alleles for other traitsduring gamete formation. We have no wayof determining which allele will go into whichgamete, it is random!
  15. 15. Mendel’s Work led to…The Scientific Field of Molecular Genetics= study of structure and function ofchromosomes and genes **Mendel’s “factors” = genes
  16. 16. MOLECULAR GENETICS Mendel did not know the structure of DNA or that there were genes during his research Gene = segment of DNA on a CH that controls a trait Chromosomes (CH’s) occur in pairs = there are 2 genes responsible for each trait  1 from mom  1 from dad
  17. 17. Molecular Genetics continued…  Allele = each different form of a gene, during meiosis each gamete gets one form of this gene Rr R = dominant allele r = recessive allele
  18. 18. Example of Alleles
  19. 19. How to follow allele inheritance= Genetic Crosses
  20. 20. Genetic Crosses Objectives1. Phenotype of the parents & offspring= how a trait shows up physically in theorganism
  21. 21. Genetic Crosses Objectives2. Genotype= the alleles (genes) that the organism hasinherited  homozygous (the same alleles)  recessive rr  dominant RR  heterozygous (different alleles) Rr
  22. 22. Genotype
  23. 23. Type of Crosses and Inheritance1. Monohybrid cross= following inheritance of 1 trait from generationto generation
  24. 24. Types of Crosses continued…2. Dihybrid= following inheritance of 2 traits from generationto generation
  25. 25. Crosses3. complete dominance= dominant phenotype always masks therecessive phenotype when the dominantallele is present
  26. 26. Crosses4. incomplete dominance= both phenotypes mix together in aheterozygous individual
  27. 27. Crosses5. codominance= both phenotypes show up equally in aheterozygous individual B = Black cat W = White cat
  28. 28. In order to set up a cross, you use1. Monohybrid Cross Punnett Square 1 trait!2. Dihybrid Cross Punnett Square 2 traits!
  29. 29. What if you don’t know thegenotype of an organism…only thephenotype You Perform A Test Cross= used if the individual of interest shows thedominant phenotype (physicalcharacteristic) but you don’t know if it isheterozygous or homozygous dominantgenotypically (what alleles the individualactually inherited)
  30. 30. A TEST CROSS= cross that unknown individual with ahomozygous recessive and look at theiroffspring
  31. 31. Test Cross Results Look at offpring of test individual and the homozygous recessive parent All dominant offspring = test individual is homozygous dominant (PP) Any recessive offspring at all = test individual is heterozygous (Pp)
  32. 32. Another Test Cross Example
  33. 33. ProbabilityProbability= likelihood that a specific event willoccur, expressed as a decimal, percentageor fraction # times an event is expected to happen # of opportunities for an event to happen
  34. 34. Chapter 12 – HumanInheritance Types of Genetic Traits/Disorders & how they are inherited:1. Single-allele traits= controlled by 1 allele of a gene (200) i.e. Huntington’s Disease (HD), Cystic fibrosis, sickle cell anemia
  35. 35. Human Inheritance Types…2. Multiple-allele traits= controlled by 3+ alleles of the same gene thatcode for a single trait i.e blood types
  36. 36. AA = buds SS = spikes AS = spikes & buds NN=none AN = buds SN = spikes
  37. 37. UniversalAcceptorUniversalDonor
  38. 38. Human Inheritance Types…3. Polygenic Traits= a trait controlled by several genes i.e. skincolor, eye color, human height
  39. 39. Human Inheritance Types…5. Sex-Linked/Sex-Influenced traits= presence of male or female chromosome andsex hormonesSex-Linked – the gene for trait is on the X or Y v.Sex-Influenced – the gene isn’t on the X or Y, butthe expression (phenotype) is affected by thehormones made by being XX (female) or XY(male)
  40. 40. Sex-Linked
  41. 41. Examples of Sex-Linked Traitsi.e. hemophilia, colorblindness, musculardystrophy, baldness
  42. 42. Sex-Linkage= presence of a gene on a sex chromosome (X orY)1) X-linked – genes found on the X chromosome and inherited when the individual receives an X during fertilization  Most common type  MostX-linked diseases/traits are recessive (need 2 copies of allele to show disease/trait physically)
  43. 43. X-linked continued…  Father to son transmission is IMPOSSIBLE!  Youcan be a “carrier” and not have the disease  Morecommon in males! (they only need 1 copy!)Examples: musculardystrophy, hemophilia, color-blindness, fragile X-syndrome, protanopia, Aicardi syndrome
  44. 44. Male Female The "a" The "a" recessive recessiveallele will be allele will notexpressed in be expressed his in herphenotype phenotype
  45. 45. Y-Linked Traits= genes found on the Y chromosome andinherited when the individual receives a Y (andbecome a male) during fertilization  Only males can have these diseases/traits  Very rare Examples: Klinefelter syndrome (XXY), Jacobs Syndrome (XYY)
  46. 46. What does it mean to “carry” atrait?Carrier= when an organism has 1 copy of an allele thatcauses a recessive disorder but does not presentthat disorder/trait physically XdX = carrier, female XdXd = has disorder, female XdY = has disorder, male XY = doesn’t have disorder and is not a carrier!, male
  47. 47. = A PEDIGREE
  48. 48. What is a PEDIGREE??= family record that shows how a trait is inherited over several generations ~ is actualinheritance Shows: and not “possible” 1. Sex of individuals 2. “marriages” 3. Number of offspring 4. Type of trait a. Single- allele b. Sex-linked
  49. 49. How to Read a Pedigree