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A genetics lab homework assignment from a fall 2006 bio 184 class. The assignment covers various topics such as gene interactions, map distance, and punnett squares. Students are asked to analyze the genotypes and phenotypes of different organisms, including tribbles, red spiders, and water lilies, to determine the location and interaction of specific genes.
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BIO 184 Fall 2006
Please write all your final answers in the space provided below each question.
1. (12 points) Among tribbles (an alien species indigenous to Star Trek), the ability to emit a high pitched purring sound is under the control of a single gene. Similarly, the abilities to utilize triticale grain as an energy source and to produce large litter sizes are also controlled by single genes. P = purring T = can utilize triticale L = large litter sizes P = cannot purr t = cannot utilize tritacle l = small litter sizes A female tribble with the genotype (Pp,Tt,Ll) is crossed to a non-purring male who cannot utilize triticale and is homozygous for the allele that causes small litter sizes. From this mating, the following offspring are produced: 567 PTl 600 ptL 22 PTL 18 ptl 2 PtL 0 pTl 103 pTL 98 Ptl a. Which gene is in the middle? How do you know? b. Calculate the map distance between adjacent genes. Show all your work. c. Draw a map of the three genes, indicating the distance between adjacent genes, which gene is in the middle, and the total distance between the two outside genes.
BIO 184 Fall 2006
2. (10 points) Most red spiders have long legs. However, rare short-legged spiders are occasionally born. To study the genetics of leg length in these spiders, you cross a pure-breeding long-legged spider with a pure-breeding short-legged spider to produce an F1 generation, all of which have long legs. You then cross the F1 generation spiders to one another to produce an F generation, with the following results: 269 long-legged spiders 19 short-legged spiders Provide two fundamentally different genetic explanations for this result. 3. (10 points) In water lilies, leaf morphology is under the control of 2 genes: Large (LL) Medium-sized (LL’) Small (L’) Round (R) Oblong (r) A plant pure-breeding for large, oblong leaves is crossed with a plant pure-breeding for small, round leaves. The F1 plants are then crossed to one another to produce an F generation. a. Use a Punnett Square to predict the expected phenotypic ratios that would be observed among the F2s.
BIO 184 Fall 2006 b. Map the distance between the genes. Show your calculation.