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Drosophila Genetics I

Drosophila Genetics I. Inheritance, Autosomal genes vs. Sex Linked genes, Monohybrid and Dihybrid Crosses * Lab manual protocol will not be used. Lab Objectives. To have a first hand look at how genes are inherited in the model organism Drosophila melanogaster (Fruit Fly)

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Drosophila Genetics I

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  1. Drosophila Genetics I Inheritance, Autosomal genes vs. Sex Linked genes, Monohybrid and Dihybrid Crosses *Lab manual protocol will not be used

  2. Lab Objectives • To have a first hand look at how genes are inherited in the model organism Drosophila melanogaster (Fruit Fly) • To develop a better understanding of genetics by conducting monohybrid and dihybrid crosses. • To have a basic knowledge of working with Drosophila as a model organism

  3. Overview • Review Mitosis and Meiosis • Review Concepts of Genetics • Drosophilamelanogaster • Background Information • Applied Genetics

  4. I. Mitosis and Meiosis

  5. II. Genetics Review

  6. Allele-alternate forms of a given gene (brown or blue eyes) Independent assortment- random distribution of unlinked genes into gametes. Linked Genes- genes located on the same chromosome tend to be inherited together. The alleles do not assort independently. Sex linked genes- genes located on a sex chromosome (e.g. white eyes in Drosophila) Crossing over- reciprocal exchange of genetic material between non-sister chromatids during meiosis I (performed in pipe cleaner exercise during meiosis).

  7. Alleles on Chromosomes

  8. Mendel’s Law of Segregation The two alleles present for a gene will separate during gamete formation For example: AA will segregate into A and A Aa will segregate into A and a

  9. The Law of Independent assortment “Each pair of alleles segregates into gametes independently” (Campbell) For examples: AaBb will segregate and form 4 different gametes: AB, Ab, aB, and ab.

  10. Thomas Hunt Morgan • State College of Kentucky (later the University of Kentucky), B.S. • Johns Hopkins University, Ph. D. • Nobel Prize for Physiology / Medicine in 1933.

  11. Chromosome theory of heredity • Found that genes are located on chromosomes • Discovered Sex-Linkage (module 10) • Worked with Drosophila

  12. Why Drosophila? • Short Generation Time • Easy to Maintain • 4 large chromosomes • Easily identifiable • markers (mutant • phenotypes) • For more information chapter 21 in Campbell. • http://flymove.uni-muenster.de/

  13. Drosophila life cycle • Egg • Larva • Pupa • Adult The whole life cycle is about 14 days at RTº

  14. CHROMOSOMES • Sex -chromosomes responsible for determining sex of an individual • Autosomal- chromosome that is not directly involved in determining sex. Female Male XX /XY II III IV Sex -----------Autosomal-----------

  15. Sexing adult flies (p.65)

  16. ‘white eye’ phenotype WT White eye mutant

  17. Example Phenotypes Ebony body Curled wings Vestigial wings W.T.

  18. Genotype Phenotype wt (homozygous) + / + vg / + wt (heterozygous) Nomenclature Autosomal Genes (use + for wt allele) Convention dictates that we denote genotype in the following fashion: vg / vg +_ mutant wt (homo. or het.)

  19. Genotype Phenotype wt (homozygous) + / + vg / + wt (heterozygous) Autosomal Gene Nomenclature Wild-type genes located on autosomal chromosomes are donated “+” by convention (note that a separate system is used for sex-linked genes--module 10) (Each allele is represented and is seperated by a “/”) vg / vg mutant

  20. wt ebony White body Terminology Wild type- the normal or most common phenotype in a population. Mutant Phenotype- traits that are alternates to the wild type. Changes due to mutations in the wild type.

  21. Monohybrid Cross • Cross breeding organisms while tracking one trait.

  22. Example Monohybrid Cross ++ x vgvg (Wildtype) (Vestigial)

  23. F1 Genotypes F1 Phenotypic Ratio: wt

  24. We then cross two F1 progeny…… +vg x +vg (heterozygous) (heterozygous)

  25. Refer to Assignment I Worksheet

  26. Dihybrid Cross • Cross breeding organisms while tracking two traits

  27. Example Dihybrid Cross ++ ++ x bb vgvg (Wild type) (Black vestigial) This is not the cross that you will design on your worksheets. See worksheet for Assignment I for fly lab and complete the dihybrid cross.

  28. Test Cross A testcross is a valuable way to use a genetic cross to determine the genotype of an organism that shows a dominant phenotype but unknown gentoype.

  29. Example Test Cross +_ x vgvg (Unknown) (Vestigial) If the F1 progeny are all WT the genotype of the unknown fly is +/+. If the F1 progeny are a mix of wild-type and vestigial flies, the genotype of the unknown fly is +vg.

  30. Goals • Observe Male/Female flies • Observe various phenotypes of flies • Comprehend: • Test Cross • Monohybrid Cross • Dihybrid Cross • Chi Square Test View these all in virtual flylab.

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