WS3. GeneticsProblems.docx

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Foundations of BiologyLab Project 2 WORKSHEET 3 – GENETICS PROBLEMS (20 pts. + 1 pt. bonus): Arya Sajadian 1. (4 pts. total) A true-breeding mutant strain of Drosophila has brown-colored eyes. When males of this strain are mated to wild type Drosophila females with red colored eyes, all of the F1 offspring have red eyes. When the F1 males and females are mated, they produce red- and brown-eyed offspring in a 3:1 ratio. a. Is the brown eye mutation dominant or recessive with respect to the wild type allele for eye color? Briefly explain. [1 pt.] Recessive, as since the wild type in the first gen is homozygous dominant, all of F1 are carriers, and the 3:1 stems from the need for both recessive alleles and no dominant ones present, which leads to progeny of RR, Rr, Rr, and rr. b. Using the format for naming mutant and wild type alleles of Drosophila genes (described on p. 86 of the lab manual), assign allele designations and write out the genotypes for the cross of the brown-eyed males and red-eyed females and their F1 offspring. You can assume that the gene is located on an autosome. [2 pts.] Red are the wild type with designation w+ w+, while brown eyes are the mutated alleles with w w designation. Crossing them leads to a w+ w genotype. c. When F1 males and females in 1b are crossed to each other, what are the genotypes of their F2 offspring? [1 pt.] Either w+ w+ or w+ w 2. (8 pts. total) When a female fruit fly with notched wings is mated to a male with wild type rounded wings, all the F1 offspring have notched wings. When a male with notched wings is mated to a female with wild type rounded wings, all the male offspring have wild type rounded wings and all of the female offspring have notched wings. You can assume that the parent male and females are true-breeding (none of the parent flies are heterozygous). a. Explain the observed pattern of inheritance. Specifically, state whether the notched wing trait is dominant or recessive and whether it is X-linked or on an autosome. [2 pts.] 1

Foundations of BiologyLab Project 2 Notched wing seems to be linked to the X chromosome, and dominant due to the fact that a female with notched passes it all onto all offspring, but a male having the linked trait only can pass it to females b. Again, using the format for Drosophila genes, assign genotypes to the two parent crosses and their F1 offspring [4 pts.] Cross 1 notched wing females x rounded wing males: X*Y* female notched + XY male wild F1 offspring: X* X females and X* Y males (mutant phenotype present in all) Cross 2 notched wing males x rounded wing females: X* Y male notched + XX female wild F1 offspring: XY males + X* X females (mutant phenotype only present in females) c. What F2 phenotypes and ratios are expected if the F1 offspring of Cross 2 are mated with each other? Show you work. [2 pts.] Cross 2 will have X* X (female notch), XX (female wild), X* Y (male notch), and XY (male wild) in equal ratios (1:1:1:1), with the ratio of the notch phenotype also being 1:1 (50%) 3. (4 pts.) A student performs the following dihybrid cross with fruit flies: True-breeding males with fat body shape and wild type gray body color are mated to true-breeding females with normal body shape and ebony body color. The fat body shape and ebony body color mutations are both recessive. The body shape gene is on located on the second chromosome while the body color gene is located on the third chromosome. a. Assign letter designations to each gene and the alleles. Write out the cross and the expected F1 offspring. [2 pts.] B+ B+ = Normal body (wild) B B = Fat Body e+ e+ = grey (wild) 2

Foundations of BiologyLab Project 2 e e = ebony Cross: BB e+e+ (male) + B+B+ ee (female) F1: B+B e+ e = Normal grey (wild in both phenotypes) b. If the F1 hybrid female fruit flies are mated to “tester” males with fat body shape and ebony body color, what phenotypes and ratios are expected in the F2 generation? [2 pts.] Parent Phenotypes: B+B e+ e = Normal grey BB ee = ebony fat Non parent phenotypes: BB e+e = fat grey B+B ee = normal ebony Equal ratio (1:1:1:1) 4. (5 pts.) The kinked ( ki ) and the striped ( sr ) genes of Drosophila are linked, and are located on chromosome 3 at map positions 47.6 and 62, respectively. The recessive allele ( ki ) of the kinked gene causes kinked bristles instead of straight. The recessive allele ( sr ) of the striped gene causes stripes on the back of the thorax that are not present in wild type flies. Homozygous male fruit flies with “kinked” bristles and “striped” thorax are mated to homozygous females with normal bristles and unstriped thorax. a. Draw out the cross described above. Illustrate the pair of 3 rd chromosomes, including the kinked and striped alleles, of the male and of female flies. [2 pts.] 3

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Foundations of BiologyLab Project 2 b. Draw the chromosomes and alleles for the F1 offspring of the cross in 4a. [1 pt.] 4

Foundations of BiologyLab Project 2 c. If the F1 hybrid female fruit flies are mated to tester males with kinked bristles and striped thorax, what phenotypes are expected in the F2 generation? Predict the % of each of the different phenotypes. [2 pts.] K+KS+S KSKS K+KSS KKS+S equal ratio (25% for each) 5

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