1. Genetics Refresher

2. FIGURE 3.1 Gregor Johann Mendel (1822—1884)  Mendel discovered a mechanism of inheritance while conducting experiments on garden peas at a monastery in Brunn, Austria (now Brno, Czech Republic).

3.  The table summarizes results of Mendel’s experiments following seven characters during crosses of the garden pea. For example, Mendel observed that in the F1 generation, the character (or trait), seed color, occurred 6,022 yellow (dominant) : 2,001 green (recessive), a ratio of 3.01:1, very close to his predicted ratio of 3:1.

4. Mendel’s experimental method  In this experiment of a cross between true breeding white- and purple-flowered plants, Mendel pried open the surrounding petals of the purple-flowered plant and removed the male part, thus preventing self-fertilization. Then he dusted the anther with pollen he had selected from the white-flowered plant. The resulting seeds were planted and grew, all producing purple flowers.

5. Independent segregation—single trait, flower color  Mendel’s cross of pea plants for flower color started with true breeding white-flowered (recessive) and purple-flowered (dominant) plants. All F1 offspring of this cross were purple-flowered, and genetically heterozygous (Pp). When these were crossed, the resulting F2 offspring averaged 3 purple- for every 1 white-flowered plant, a 3:1 phenotypic ratio. However, the ratio of genotypes is 1:2:1 (1PP: 2Pp : 1pp).

6. Testcross  By just looking at a dominant phenotype, for example, this plant with purple-flowers, you would not know if it was homozygous or heterozygous for the dominant allele. To determine its genotype, Mendel performed a testcross. In this illustration, the dominant phenotype (unknown genotype) was crossed with a plant known to be homozygous recessive, for example, the white-flowered plant. If all offspring are purple (Alternative 1), then the unknown flower is homozygous dominant; if offspring are half and half, purple and white (Alternative 2), then the unknown flower is heterozygous.

7. Independent assortment—multiple traits, seed shape and seed color  Mendel followed two traits together to see if they influenced each other. Vertically at left, the phenotypic outcomes into the F2 generation are followed for seed shape—round (dominant) and wrinkled (recessive); and seed color—yellow (dominant) and green (recessive). An underline in a genotype indicates that either a dominant or a recessive allele is possible. If the alleles assorted or moved into gametes without affecting each other, then the predicted ratio is 9:3:3:1, which is about what Mendel observed. Vertically at the right, the allele combinations resulting from each successive cross are mapped, showing the genotypes.

11. A-T Base Pair Adenine is a purine; thymine is a pyrimidine.

12. G-C Base Pair Guanine is a purine; Cytosine is a pyrimidine.

15. Transcription animation

16. Translation animation

17. Types of Mutations  Point mutation –Synonymous –Transition –Transversion  Frame-shift mutation  Stop mutation  Translocation  Fusion

22. Gene mutations

23. Normal hemoglobin Abnormal hemoglobin

26. Chromosome mutations

27. Mutation Rates  Classic rate is approximately 1 X 10 -6 per locus.  In other words, roughly one mutation for every million replications  Different types of mutations occur at different rates

28. Some Mutation Rates OrganismCharacter (gene gene)Rate E. coliLactose fermentation lac - to lac + 2 X 10 -7 AlgaeStreptomycin sensitivity Str-d to str-s 1 X 10 -6 CornShrunken seeds Sh to sh 1 X 10 -5 DrosophilaYellow body Y to y 1 X 10 -4 MouseDilute coat color D to d 3 X 10 -5 HumanNormal to hemophilic3 X 10 -5 HumanNormal to albino3 X 10- 5

29. Some mutation rates for human genesmutation rates

30. Types of Mutagens  Ultraviolet radiation  Ionizing radiation  Chemical mutagens

31. Diploidy  Most organisms have two sets of chromosomes  In humans, 22 sets of autosomes and 1 pair of sex chromosomes  Each set with about 3 billion nucleotides

32. Normal human male karyotype Normal human female karyotype

33. Trisomy 21

34. Diploidy is important for reproduction  Haploid gametes formed by meiosis  Fertilization results in combination of two haploid gametes to form diploid zygote

35. Mitosis and meiosis  In meiosis, chromosomes replicate, homologous pairs align, and each duplicated homologue separates during cell division. Then, a second cell division separates replicated chromosomes, and four haploid daughter cells (gametes) are produced. In mitosis, chromosomes replicate, but one cell division separates replicated chromosomes into two diploid daughter cells.

36. Meiosis results in the reduction of the chromosome number from the diploid state to the haploid number.

37. In the process of fertilization, two haploid games unite and the diploid state is restored.

38. Diploidy results in a double set of chromosomes  Genetic locus – location of a gene on a chromosome  Genotype – an organism’s complement of genes  Phenotype – physical expression of the genotype  Alleles – different forms of a gene  Homozygous – describes individual with two similar alleles for a trait  Heterozygous – describes individual with two different alleles for a trait

39. Mendelian Ratios

40. Recombination may occur during meiosis

43. Gene linkage  Two fruit fly genes reside on the same chromosome—wing length and eye color. Because they are located on the same chromosome, they ride together into the gametes, thereby reducing the number of genotypes and phenotypes possible.

44. Multiple genes, one trait  Polygenetic inheritance is illustrated with three genes, A, B, and C; hence, six alleles, for wheat seed color. Alleles contributing to the color are indicated by a capital letter; others not contributing are in lower case. In each generation, the six alleles are shown by circles— solid if contributing and open if not adding to seed color. In the F2 generation, the phenotypes expressed are additive, producing a continuous range of seed color. If graphed by frequency, they form a bell-shaped curve.

45. FIGURE 3.13 Polygenic Trait in Humans—Height  Aligned by height, the students show a range of continuous phenotypic variation, with most in the middle.

46. FIGURE 3.11 Multiple Alleles, One Trait  In humans, the gene that controls blood type has three different alleles: A, B, and O, resulting in four different blood phenotypes: A, B, AB, O, specifically type A (A/A or A/O); type B (B/B or B/O); type AB (A/B); and type O (O/O).

47. Mendelian inheritance versus Blending