5. (4 points): A cross of two strains of budding yeast produces unordered tetrads. In the parental strains, the genotypes for two different pairs of genes on two different chromosomes are: + + X a b, and g + X + h. The results are shown; each column is a tetrad, with total numbers at the bottom: For genes a and b: a b + b a + Are a and b linked or unlinked? ________ a b + + a + + + a b + b + + a + + b 270 68 10 For genes g and h: + + g + + h Are g and h linked or unlinked? ________ + + g + g h g h + h g + g h + h + + 159 174 23 The map distance between linked genes is given by (1/2)[#TT] + 3[#NPD] X 100 Total # of tetrads What is the map distance between the genes that are linked (don't forget the units)? __________ This calculated map distance is probably not a very accurate estimate of true physical distance. Why not?
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- Look at the tetrad data for genes a and b. - The tetrad types are: - Parental ditype (PD): \( a b \) and \( + + \) = 270 - Non-parental ditype (NPD): \( a + \) and \( + b \) = 10 - Tetratype (TT): \( a b \), \( a + \), \( + b \), and \( + + \) = 68 Show more…
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2. Analysis of unordered yeast tetrads from the cross of a haploid strain with genotype + + + with a strain of genotype a b c yielded the following data. The genotypes of four spores from the same tetrad are listed on each horizontal line. Tetrad Class Spores Number of Asci 1. a b c a b c + + + + + + 36 2. a b c a + c + b + + + + 14 3. a + + a + + + b c + b c 32 4. a b + a + + + b c + + c 16 5. a b + a b + + + c + + c 2 a. Which of these genes are linked, and what is the map distance between them? Show your work. (4 pts) b. Draw a map that illustrates the relative locations of these three genes and their respective centromeres. (2 pts)
Sri K.
Analysis of unordered yeast tetrads from the cross ade ura⁰ x ade⁰ ura yielded the following data: Tetrad class Spore Phenotypes # of Asci 1 ade ura⁰ ade ura⁰ ade⁰ ura ade⁰ ura 56 2 ade ura⁰ ade ura ade⁰ ura⁰ ade⁰ ura 40 3 ade ura ade ura ade⁰ ura⁰ ade⁰ ura⁰ 2 What is the map distance between the genes? a. The genes are not linked b. 20.4% c. 42.9% d. 40.8% e. 22.4%
A yeast geneticist irradiates haploid cells of a strain that is an adenine-requiring auxotrophic mutant, caused by mutation of the gene ade1. Millions of the irradiated cells are plated on minimal medium, and a small number of cells divide and produce prototrophic colonies. These colonies are crossed individually with a wildtype strain. Two types of results are obtained:(1) prototroph × wild type : progeny all prototrophic(2) prototroph × wild type : progeny 75% prototrophic, 25% adenine-requiring auxotrophsa. Explain the difference between these two types of results.b. Write the genotypes of the prototrophs in each case.c. What progeny phenotypes and ratios do you predict from crossing a prototroph of type 2 by the original ade1auxotroph?
Katlin K.
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