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Patterns of Inheritance

Patterns of Inheritance. Chapter 13. LEARNING OBJECTIVE 1. Define the following terms relating to genetic inheritance: dominant and recessive ; homozygous and heterozygous ; genotype and phenotype. KEY TERMS. DOMINANT Said of an allele that is always expressed when it is present

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Patterns of Inheritance

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  1. Patterns of Inheritance Chapter 13

  2. LEARNING OBJECTIVE 1 • Define the following terms relating to genetic inheritance: dominantand recessive; homozygousand heterozygous; genotypeand phenotype

  3. KEY TERMS • DOMINANT • Said of an allele that is always expressed when it is present • RECESSIVE • Said of an allele that is not expressed in the presence of a dominant allele

  4. KEY TERMS • HOMOZYGOUS • Possessing a pair of identical alleles for a particular gene • HETEROZYGOUS • Possessing a pair of unlike alleles for a particular gene

  5. KEY TERMS • GENOTYPE • Genetic makeup of an individual • PHENOTYPE • Physical expression of an individual’s genes

  6. Cross-Pollination in Garden Peas

  7. (c) Anthers snipped from the flower. (a) Reproductive structures of flowers are enclosed by petals. (d) Pollen from a different flower brushed onto tip of carpel. Anther Carpel Carpel (b) Petals opened to reveal male and female reproductive structures. (e) Fertilized carpel produces seeds, which are planted. (f) Offspring are observed. Fig. 13-1, p. 256

  8. Characters in Mendel’s Study

  9. Flower color Seed color Pod color Pod shape Yellow Green Purple Seed shape Round Wrinkled White Green Yellow Pinched Inflated Stem height Flower position Axial Terminal Tall Short Fig. 13-2, p. 257

  10. Mendel’s Experiments

  11. Parents X Tall plant Short plant Fig. 13-3a, p. 258

  12. Tall plant Tall plant Tall plant Tall plant First generation F1 offspring All tall plants Fig. 13-3b, p. 258

  13. Tall plant Tall plant Tall plant Short plant Second generation F2 offspring 3 tall:1 short Fig. 13-3c, p. 258

  14. LEARNING OBJECTIVE 2 • Distinguish among chromosomes, genes, and alleles

  15. KEY TERMS • LOCUS • Location of a particular gene on a chromosome • ALLELE • One of two or more alternative forms of a gene

  16. Genes • Genes occur in pairs and are inherited as parts of chromosomes • Alleles are carried on homologous chromosomes • may be alike (homozygous) or unlike (heterozygous)

  17. Segregation of Alleles

  18. Homologous chromosomes METAPHASE I T t t T METAPHASE II T T t t T T t t T t Fig. 13-4, p. 259

  19. Homologous chromosomes METAPHASE I T T t t METAPHASE II t t T T T t t T T t Stepped Art Fig. 13-4, p. 259

  20. Homologous Chromosomes

  21. Alleles controlling height: Gene loci A pair of alleles Short Tall Alleles controlling flower color: Red White These genes are not alleles (a) These chromosomes are nonhomologous. Each chromosome is made up of thousands of genes. A locus is a specific place on a chromosome where a gene is located. (b) These chromosomes are homologous. Alleles are members of a gene pair that occupy corresponding loci on homologous chromosomes. (c) Alleles govern the same character but do not necessarily contain the same information. Fig. 13-5, p. 260

  22. LEARNING OBJECTIVE 3 • Solve simple genetics problems involving monohybrid and dihybrid crosses

  23. Monohybrid Cross • A cross between two individuals in which only one character is being studied • A cross between one homozygous dominant and one recessive individual yields F1offspring that are all heterozygous • A cross between heterozygous individuals yields a 3:1 phenotypic ratio in F2offspring

  24. Monohybrid Cross

  25. Fig. 13-6a, p. 261

  26. F1 Phenotypes True-breeding short parent (recessive) tt Tall Tt Tall Tt True-breeding tall parent (homozygous dominant) t t t t T Tt T Tt TT Tall Tt Tall Tt T Tt Tt T (a) When a genetically pure tall garden pea is crossed with a genetically pure short garden pea, all the offspring are tall. Fig. 13-6a, p. 261

  27. Fig. 13-6b, p. 261

  28. F2 Phenotypes Tt F1 plant Tall TT Tall Tt t T F1 plant t T T T TT Tt Tt Tall Tt Short tt t T Tt tt (b) When two individuals of the F1 generation are crossed, the F2 generation is produced. The phenotypic ratio of the F2 is 3:1. Fig. 13-6b, p. 261

  29. Dihybrid Cross • A cross between two individuals in which two characters are being studied • A cross between one individual homozygous dominant for both characters and one recessive for both characters yields F1 offspring heterozygous for both characters • A cross between two heterozygous individuals yields a 9:3:3:1 phenotypic ratio in F2 offspring

  30. Dihybrid Cross

  31. Fig. 13-8a, p. 263

  32. rryy True-breeding parent F1 Phenotypes ry ry ry ry True-breeding parent RrYy RrYy RY RY RrYy RrYy RRYY RY RY RrYy RrYy RrYy RrYy All round yellow (a) When Mendel crossed a true-breeding plant having round and yellow seeds with a true-breeding plant having wrinkled and green seeds, the seeds produced by the F1 plants were all round and yellow. Fig. 13-8a, p. 263

  33. Fig. 13-8b, p. 263

  34. F2 Phenotypes F1 plant RrYy RY Ry rY ry RrYY RrYy RRYY RRYy ry rY Ry RY F1 plant RRyy RrYy RRYy Rryy RrYy RY RRYY RrYY RRYy RY Rryy RrYy Ry RRYy RRyy Ry RrYy RrYY RrYy rrYY rrYy RrYy rrYy rY rY RrYY rrYY Rryy rryy RrYy rrYy ry ry RrYy Rryy rrYy rryy Phenotypic ratio is 9:3:3:1 (b) When two heterozygous individuals are crossed, the ratio of phenotypes is 9:3:3:1 (9 round yellow:3 round green: 3 wrinkled yellow:1 wrinkled green). Fig. 13-8b, p. 263

  35. LEARNING OBJECTIVE 4 • Explain how a test cross is used to determine the genotype of an individual exhibiting a dominant phenotype

  36. Test Cross • An experimental cross that determines if an individual with a dominant phenotype is homozygous or heterozygous • Dominant individual is crossed with a recessive individual (Example: tt) • If the dominant individual is heterozygous, some of offspring should have the recessive phenotype

  37. Test Cross

  38. Fig. 13-7a, p. 262

  39. Phenotypes of offspring Recessive tt Tall Tt Tall Tt t t Homozygous dominant t t T Tt T Tt TT Tall Tt Tall Tt T Tt Tt T (a) If a homozygous tall garden pea is crossed with a short one, all the offspring are tall. Fig. 13-7a, p. 262

  40. Fig. 13-7b, p. 262

  41. Phenotypes of offspring Recessive tt Tall Tt Tall Tt t t Heterozygous t t T Tt T Tt Tt t t Short tt Short tt tt tt (b) If any of the offspring are short, the tall garden pea must be heterozygous. Fig. 13-7b, p. 262

  42. LEARNING OBJECTIVE 5 • Define linkage • Explain why linked genes are sometimes not inherited together

  43. KEY TERMS • LINKAGE • Grouping of genes on the same chromosome

  44. Linked Genes 1 • Two linked genes tend to be inherited together because genes that occur on the same chromosome tend to remain with each other during meiosis

  45. Linked Genes 2 • Sometimes linked genes are not inherited together • Failure of linked genes to stay together is the result of crossing overof segments of homologous chromosomes during prophase I of meiosis

  46. Linkage and Crossing-Over

  47. B A A B b b B B A a b B Meiosis I a B a b A B A b Meiosis II Four haploid cells produced Parental type Recombinant type Recombinant type Parental type Fig. 13-9, p. 266

  48. LEARNING OBJECTIVE 6 • Contrast incomplete dominance and polygenic inheritance

  49. KEY TERMS • INCOMPLETE DOMINANCE • A condition in which neither member of a pair of contrasting alleles is completely expressed when the other is present • A heterozygote exhibits a phenotype intermediate between those of its two parents

  50. Incomplete Dominance

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