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

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Presentation on theme: "Drosophila Genetics I Inheritance, Autosomal genes vs. Sex Linked genes, Monohybrid and Dihybrid Crosses * Lab manual protocol will not be used."— Presentation transcript:

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  Drosophila melanogaster Background Information Background Information Applied Genetics 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. 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. 

13 Drosophila life cycle  Egg  Larva  Pupa  Adult The whole life cycle is about 14 days at RT º

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

15 Sexing adult flies (p.65)

16 ‘white eye’ phenotype ‘white eye’ phenotype WTWhite eye mutant

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

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

19 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 “/”) GenotypePhenotype + / + wt (homozygous) vg / +wt (heterozygous) vg / vgmutant

20 wtebonyWhite body 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. Terminology

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

22 Example Monohybrid Cross ++ x v g v g (Wildtype) (Vestigial)

23 F1 Genotypes vgvg ++vg+vg ++vg+vg F1 Phenotypic Ratio: wt

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

25

26 Refer to Assignment I Worksheet

27 Dihybrid Cross  Cross breeding organisms while tracking two traits

28 Example Dihybrid Cross x bb v g v g (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.

29 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. Test Cross

30 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.

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


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