drosophila genetics i inheritance, autosomal genes vs. sex linked genes, monohybrid and dihybrid...
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Drosophila Drosophila Genetics IGenetics I
Inheritance, Autosomal genes vs. Inheritance, Autosomal genes vs. Sex Linked genes, Monohybrid Sex Linked genes, Monohybrid
and Dihybrid Crossesand Dihybrid Crosses
**Lab manual protocol will not be usedLab manual protocol will not be used
Lab ObjectivesLab Objectives To have a first hand look at how genes are To have a first hand look at how genes are
inherited in the model organism inherited in the model organism Drosophila melanogaster Drosophila melanogaster (Fruit Fly)(Fruit Fly)
To develop a better understanding of To develop a better understanding of genetics by conducting monohybrid and genetics by conducting monohybrid and dihybrid crosses. dihybrid crosses.
To have a basic knowledge of working To have a basic knowledge of working with with Drosophila Drosophila as a model organismas a model organism
OverviewOverview
Review Mitosis and MeiosisReview Mitosis and Meiosis Review Concepts of GeneticsReview Concepts of Genetics DrosophilaDrosophila melanogastermelanogaster
Background InformationBackground Information Applied GeneticsApplied Genetics
I. Mitosis and MeiosisI. Mitosis and Meiosis
II. Genetics ReviewII. Genetics Review
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).
Alleles on ChromosomesAlleles on Chromosomes
Mendel’s Law of Mendel’s Law of SegregationSegregation
The two alleles present for a gene will The two alleles present for a gene will separate during gamete formationseparate during gamete formation
For example: For example:
AAAA will segregate into will segregate into A A and and AA
AaAa will segregate into will segregate into AA and and aa
The Law of Independent The Law of Independent assortmentassortment
““Each pair of alleles segregates into Each pair of alleles segregates into gametes independently” (Campbell)gametes independently” (Campbell)
For examples:For examples:AaBb AaBb will segregate and form 4 different gametes:will segregate and form 4 different gametes:
AB, Ab, aB, AB, Ab, aB, andand ab ab. .
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.
Chromosome theory of heredity
Found that genes are located on chromosomes
Discovered Sex-Linkage (module 10)
Worked with Drosophila
Why Why DrosophilaDrosophila??
Short Generation TimeShort Generation Time Easy to MaintainEasy to Maintain 4 large chromosomes4 large chromosomes Easily identifiable Easily identifiable markers (mutant markers (mutant phenotypes)phenotypes) For more information For more information
chapter 21 in Campbell.chapter 21 in Campbell. http://flymove.uni-muenster.de/ http://flymove.uni-muenster.de/
DrosophilaDrosophila life cycle life cycle
EggEgg LarvaLarva PupaPupa AdultAdult
The whole life cycle is The whole life cycle is about 14 days at RTabout 14 days at RTºº
CHROMOSOMESCHROMOSOMES
Sex -Sex -chromosomes responsible for chromosomes responsible for determining sex of an individualdetermining sex of an individual
AutosomalAutosomal- chromosome that is not directly - chromosome that is not directly involved in determining sex.involved in determining sex.
Female
MaleXX /XY II III IV
-----------Autosomal-----------Sex
Sexing adult flies (p.65)Sexing adult flies (p.65)
‘ ‘white eye’ phenotypewhite eye’ phenotype
WT White eye mutant
Example PhenotypesExample Phenotypes
W.T. Ebony body
Vestigial wings
Curled wings
Nomenclature
Convention dictates that we denote genotype in the following fashion:
Autosomal Genes (use + for wt allele)
Genotype Phenotype
+ / + wt (homozygous)
vg / + wt (heterozygous)vg / vg+_
mutantwt (homo. or het.)
Autosomal Gene NomenclatureAutosomal Gene Nomenclature
Wild-type genes located on autosomal Wild-type genes located on autosomal chromosomes are donated “+” by conventionchromosomes are donated “+” by convention
(note that a separate system is used for sex-linked genes--module 10)(note that a separate system is used for sex-linked genes--module 10)
(Each allele is represented and is seperated by a “/”)(Each allele is represented and is seperated by a “/”)
Genotype Phenotype+ / + wt (homozygous)
vg / + wt (heterozygous)
vg / vg mutant
wt ebony White 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
Monohybrid CrossMonohybrid Cross
Cross breeding organisms Cross breeding organisms while tracking while tracking oneone trait. trait.
Example Monohybrid CrossExample Monohybrid Cross
++ x v++ x vggvvgg
(Wildtype) (Vestigial)(Wildtype) (Vestigial)
F1 GenotypesF1 Genotypes
vgvg vgvg
++ +vg+vg +vg+vg
++ +vg+vg +vg+vg
F1 Phenotypic Ratio: wt
We then cross two F1 We then cross two F1 progeny……progeny……
+vg x +vg+vg x +vg
(heterozygous) (heterozygous)(heterozygous) (heterozygous)
F2 GenotypesF2 Genotypes
vgvgvgvg+vg+vgvgvg
+vg+vg++++++
vgvg++
F2 Phenotypic Ratio: 3 wt 1 vg
Refer to Refer to
Assignment I Assignment I WorksheetWorksheet
Dihybrid CrossDihybrid Cross
Cross breeding organisms while tracking Cross breeding organisms while tracking twotwo traits traits
Example Dihybrid CrossExample Dihybrid Cross
++ ++ ++ ++ xx bb v bb vggvvgg (Wild type) (Black vestigial)(Wild type) (Black vestigial)
This is not the cross that you will design This is not the cross that you will design on your worksheets. on your worksheets.
See worksheet for Assignment I for fly lab See worksheet for Assignment I for fly lab and complete the dihybrid cross.and complete the dihybrid cross.
A testcross is a valuable way to A testcross is a valuable way to use a genetic cross to use a genetic cross to
determine the genotype of an determine the genotype of an organism that shows a organism that shows a
dominant phenotype but dominant phenotype but unknown gentoype.unknown gentoype.
Test Cross
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.
GoalsGoals Observe Male/Female fliesObserve Male/Female flies Observe various phenotypes of fliesObserve various phenotypes of flies Comprehend:Comprehend:
Test CrossTest Cross Monohybrid CrossMonohybrid Cross Dihybrid CrossDihybrid Cross Chi Square TestChi Square Test
View these all in virtual flylab.View these all in virtual flylab.