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Basic Principles of Heredity and Genetics

Explore Mendel's principles of inheritance, genetic ratios, rules of probability, linkage, sex determination, and various genetic interactions such as incomplete dominance and epistasis.

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Basic Principles of Heredity and Genetics

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  1. The Basic Principles of Heredity

  2. Phenotype Genotype Locus Allele Dominant allele Recessive allele Homozygous Heterozygous Terminology

  3. Mendel’s principles of inheritance • Segregation • During meiosis, alleles for each locus segregate • Independent assortment • Alleles of different loci distributed randomly into the gamete • Results in recombination • Production of new gene combinations not found in parent

  4. Seven characters in Mendel’s study of pea plants

  5. Oneof Mendel’spea crosses

  6. Genelociand theiralleles

  7. Monohybrid cross • Cross between homozygous parents • Differ at one locus • Dihybrid cross • Differ at two loci • Test cross • Between individual of unknown genotype and homozygous recessive individual

  8. Monohybridcross in guinea pigs

  9. Dihybridcrossinguinea pigs

  10. Test cross inguinea pigs

  11. Genetic ratios can be expressed as probabilities • Product rule predicts combined probability of independent events • Sum rule predicts combined probability of mutually exclusive events

  12. Rulesof probability

  13. Segregation • Results from homologous chromosomes separating during meiosis • Independent assortment • Orientation of homologous chromosomes on the metaphase plate determines how chromosomes are distributed

  14. Chromosomalbasis forsegregation

  15. Linkage • Tendency for a group of genes on same chromosome to be inherited together • Recombination of linked genes • Results from crossing-over in meiotic prophase I • By measuring frequency of recombination, can construct linkage map of chromosome

  16. Two-pointtest cross todetect linkagein fruit flies

  17. Crossing-over

  18. Sex chromosomes • Cells of females of many species contain two X chromosomes • Males have single X chromosome and single, smaller Y chromosome • Y chromosome determines male sex in most species of mammals

  19. Sex determinationin mammals

  20. X-linked red-green colorblindness

  21. Dosage compensation in female mammals

  22. Incomplete dominance • Heterozygote is intermediate in phenotype • Codominance • Heterozygote simultaneously expresses the phenotypes of both homozygotes

  23. Incompletedominancein four o’clocks

  24. Multiple alleles in rabbits

  25. Geneinteraction in chickens

  26. Epistasis in Labrador retrievers

  27. Norm of reaction • Range of phenotypic possibilities from a single genotype under different environmental conditions • Example is height in human • Can be modified by factors such as diet • Genes that affect height set norm of reaction • Environment molds phenotype within norm of reaction

  28. Polygenic inheritance in human skin pigmentation

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