Genetics spring 2011

Genetics spring 2011 - BSC 2010L BSC Drosophila Drosophila...

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Unformatted text preview: BSC 2010L BSC Drosophila Drosophila MENDELIAN GENETICS MENDELIAN In this lab we will: In A. Examine Bacterial Transformation A. plates plates B. Discuss Mendelian genetics and B. modes of inheritance. modes C. Study the fruit fly, its life cycle, and C. handling techniques. handling D. Cross F1 model cross flies. Bacterial Transformation plates plates A. Review Gregor Mendel Gregor MENDELIAN MENDELIAN GENETICS GENETICS Sweet pea flowers Mendelian Genetics • It’s critical to understand what a gene is and what an allele is. • Gene: linear sequence of DNA that codes for a protein, e.g. gene for flower color – Each gene has a specific location on one of the chromosomes = its loci • Allele: a particular form of the gene, e.g. gene for flower color can be the white allele or the purple allele – Each gene can have multiple versions of the DNA sequence at that loci = alleles – Different alleles can code for slightly different proteins • Because we have two copies of each chromosome (1 from mom and 1 from dad), we have two copies of each gene – Both copies can be the same allele (PP) – Or each copy can be different (Pp) Purple allele Gene for flower color Chromosome #2 (from mom) Chromosome #2 (from dad) T A G G A C C T A T C C G G G T T A T T A A Chromosome #2 (from mom) A T C C T G G A T A G G C C C A A T A A T T T White A allele A T A C Gene C for T flower A color T C C G G G T T A T T A A Chromosome #2 (from dad) A T T A T G G A T A G G C C C A A T A A T T Genotype versus phenotype Genotype A genetic cross genetic Monohybrid vs Dihybrid Cross • Monohybrid – 1 phenotypic trait followed – e.g. seed shape – 2 alleles to keep track of for seed shape: • Round (R) • Wrinkled (r) • Dihybrid – 2 phenotypic traits followed – e.g. seed shape and seed color – 2 alleles to keep track of for seed shape: • Round (R) • Wrinkled (r) – 2 alleles for seed color to track: • Yellow (Y) • Green (y) Law of Independent Assortment • Alleles from different genes get put into gametes independently of each other – Alleles for seed color (Y, y) and alleles for seed shape (R,r) assort independently • Law of Indep. Assort. only makes sense if you are talking about multiple traits/genes (dihybrid cross, trihybrid cross, etc) – Can’t discuss Law of Indep. Assort. for monohybrid cross • Law of Segregation still applies to each allele pair for a given gene – R and r still wind up in different gametes – Y and y still wind up in different gametes Mendel tracked heritable characters for three generations Mendel Mendel’s law of segregation Mendel’s The Results of Mendel’s F1 Crosses for Seven Characters in Pea Plants The The Results of Mendel’s F1 Crosses for Seven Characters in Pea Plants The A testcross testcross Testing two hypotheses for segregation in a dihybrid cross Testing P (parent cross): Y YY Y X y yy y Gametes Gametes Yy Y y X Y Yy y Gametes Gametes YY 3:1 Phenotypic Ratio 3/4 1/4 Yy yY yy 1:2:1 Genotypic Ratio 1/4 2/4 1/4 Why is this an example of the Law of Segregation? • The alleles for a given gene - seed color – get put into different gametes • Occurs during meiosis 1 – when homologous pairs separate • Note, we are talking about two alleles for a single gene getting put into different gametes Dihybrid Cross ·Yellow vs. Green · Round vs. Wrinkled Linkage • Genes do not assort independently because they are “stuck” together • If stuck on a sex chromosome: – sex linked • If stuck on an autosome: – autosomally linked • Do these types of linkage apply to a monohybrid or dihybrid cross (or both)? Autosomal Linkage P R Y R Y X r y r y ry RY RYry RYry RY RYry RYry RY RY Gametes R Y r y ry ry Gametes R Y r y ry X Autosomal Linkage P R Y R Y X r y r y RY RY Gametes R Y r y ry ry Gametes R Y r y X RY ry Gametes RY ry Gametes Autosomal Linkage P R Y R Y X r y r y RY RY Gametes R Y r y ry ry Gametes R Y r y RY RY ry Gametes ry RY RYRY RYry ry RYry ryry X RY ry Gametes Autosomal Linkage P R Y R Y X r y r y RY RY Gametes R Y r y ry ry Gametes R Y r y X RY ry Gametes RY ry Gametes Phenotypic Ratio 3/4 Round Yellow 1/4 Wrinkled Green Genotypic Ratio 1/4 RRYY 2/4 RrYr 1/4 rryy R Y R Y R Y rr yy Rr Yy r y Independent Assortment Autosomal Linkage P r y R Y r y R Y r y R Y R Y RRYY P R Y R Y RR YY X rryy r y r y r y X r y r y Gametes Gametes X R Y R Y R Y r y r y R Y r y r y Genotypic Ratio 1/4 RRYY 2/4 RrYr 1/4 Wrinkled Green 1/4 rryy Phenotypic Ratio 3/4 Round Yellow Independent Assortment P Autosomal Linkage P R Y R Y RRYY R Y X rryy r y X r y r y Gametes Gametes R Y r y X R Y r y RrYy RY Ry X RrYy rY ry 4 possible gametes R Y R Y R Y r y r y R Y r y r y Use a Punnett Square Genotypic Ratio 1/4 RRYY 2/4 RrYy 1/4 Wrinkled Green 1/4 rryy Phenotypic Ratio 3/4 Round Yellow Punnett Square Female Gametes RY RY RRYY Male Gametes rY RrYY rrYY RrYy rrYy Ry RRYy RrYy RRyy Rryy yr RrYy rrYy Rryy rryy rY Ry ry RrYY RRYy RrYy Then derive phenotypic and genotypic ratios Sex Linkage (Colorblindness) P C C X c XCXc Y XCY XCXc XCY Sex Linkage (Colorblindness) P C C X c C c X C XCXC Y XCY XCXc X cY Sex Linkage (Colorblindness) P C C X c C c X C XCXC Y XCY XCXc X cY Females C C C c c Males C 2/2 Normal 1/2 Colorblind 1/2 Normal We see different ratios for males and females Modes of Inheritance If you start with 1 parent homozygous recessive and the other homozygous dominant, then: 1. Independent Assortment Phenotypic Ratio = 9:3:3:1 2. Autosomal Linkage Phenotypic Ratio = 3:1 3. Sex-Linkage Phenotypic Ratio usually different for males and females Drosophila melanogaster Drosophila Life cycle Life A. Egg A. Egg B. Larva B. Larva C. Pupa D. Adult D. Adult Mutants Mutants A. At least ten types A. At B. Look at mutation, practice B. anesthetizing, practice sexing anesthetizing, Handling Handling • Students should work in pairs. • Transfer to anesthesia bottles. – Never knockout flies in their vials, always use knockout Never jar jar – Pink stoppers go on knockout jar only • Flynap - keep capped when not in use. • Place on index card to observe. Label card and Place pass around. pass • Place in appropriate stock jar when finished. Sexing flies Sexing A. Males have a dark A. abdomen, sex combs on the first pair of walking legs, and a rounded abdomen. and B. Females tend to be B. somewhat larger, lighter in coloration, sex combs are absent and the abdomen is more pointed. more Model Crosses Model pp. 127-129 A. We are giving you F1 flies from the following P1 crosses. You will cross these and look at ratios of F2 progeny. cross C. Details of the P1 flies. You record these on p. 133. C. – 1. Sepia dumpy females x wildtype males. – 2. Yellow white males x wildtype females. D. You must knock down these F1 flies. E. Then record phenotypes and genotypes for both sexes, on p. 133. F. Put 4-5 males and 4-5 females back into the original vial, and do F. the same into a new vial, for each of the two model crosses. the G. Prepare one vial (1 scoop medium, 1 squirt liquid, 1 shake yeast cells) for each model cross. cells) H. Do not stick them into wet medium. • • • Flies will be kept in the incubators. Use examples of crosses in the manual as illustrations. Work through the model cross predictions (Model Cross Model Predictions, pp. 125-130 - 15 points) before next lab. Predictions Slide show Slide ...
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This note was uploaded on 04/24/2011 for the course BSC 2010L taught by Professor Herrerabaerbolker during the Spring '08 term at University of Florida.

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