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Geneticsnotes ch9 bio
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Geneticsnotes ch9 bio


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  • 2. I. The History of GeneticsGenetics = field of biology devoted tounderstanding how traits are passed fromparent to offspring
  • 3. Heredity= the transmission of characteristics fromparent to offspring
  • 4. Mendel’s Experiments Gregor Mendel – the father of genetics
  • 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. Mendel’s Methods:1. grew pure purple and pure white plants for several generations (P1 generation = parent generation)
  • 7. Mendel’s Methods continued…2. cut off anthers from purple plants (malepart)
  • 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. Mendel’s Methods continued… 6. allowed self-pollination of F1 generation, producing the F2 generation75% were purple 7.25% were white
  • 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.  Mendel’s traits were carried by “factors” in each plant Each trait had 2 possible “factors” (pairs)
  • 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. 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. 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. Mendel’s Work led to…The Scientific Field of Molecular Genetics= study of structure and function ofchromosomes and genes **Mendel’s “factors” = genes
  • 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. 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. Example of Alleles
  • 19. How to follow allele inheritance= Genetic Crosses
  • 20. Genetic Crosses Objectives1. Phenotype of the parents & offspring= how a trait shows up physically in theorganism
  • 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. Genotype
  • 23. Type of Crosses and Inheritance1. Monohybrid cross= following inheritance of 1 trait from generationto generation
  • 24. Types of Crosses continued…2. Dihybrid= following inheritance of 2 traits from generationto generation
  • 25. Crosses3. complete dominance= dominant phenotype always masks therecessive phenotype when the dominantallele is present
  • 26. Crosses4. incomplete dominance= both phenotypes mix together in aheterozygous individual
  • 27. Crosses5. codominance= both phenotypes show up equally in aheterozygous individual B = Black cat W = White cat
  • 28. In order to set up a cross, you use1. Monohybrid Cross Punnett Square 1 trait!2. Dihybrid Cross Punnett Square 2 traits!
  • 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. A TEST CROSS= cross that unknown individual with ahomozygous recessive and look at theiroffspring
  • 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. Another Test Cross Example
  • 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. 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. 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. AA = buds SS = spikes AS = spikes & buds NN=none AN = buds SN = spikes
  • 37. UniversalAcceptorUniversalDonor
  • 38. Human Inheritance Types…3. Polygenic Traits= a trait controlled by several genes i.e. skincolor, eye color, human height
  • 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. Sex-Linked
  • 41. Examples of Sex-Linked Traitsi.e. hemophilia, colorblindness, musculardystrophy, baldness
  • 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. 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. Male Female The "a" The "a" recessive recessiveallele will be allele will notexpressed in be expressed his in herphenotype phenotype
  • 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. 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. = A PEDIGREE
  • 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. How to Read a Pedigree