Hartl, Jones - Genetics. Principlers and analysis - 1998 (522927), страница 57
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The two genes are in the samechromosome and recombine with a frequency of 16 percent. From the cross A b/a B × A B/a b, what is the expectedfrequency of dwarfed plants among the progeny?4.11 In the yellow-fever mosquito, Aedes aegypti, sex is determined by a single pair of alleles, M and m.Heterozygous Mm mosquitos are male, homozygous mm are female. The recessive gene bz for bronze body color(the dominant phenotype is black) is linked to the sex-determining gene and recombines with it at a frequency of 6percent. In the cross of a heterozygous bz+ M/bz m male with a bronze female, what genotypes and phenotypes ofprogeny are expected?4.12 Two genes in chromosome 7 of corn are identified by the recessive alleles gl (glossy), determining glossyleaves, and ra (ramosa), determining branching of ears.
When a plant heterozygous for each of these alleles wascrossed with a homozygous recessive plant, the progeny consisted of the following genotypes with the numbers ofeach indicated:Gl ra/gl ra 88gl Ra/gl ra 103Gl Ra/gl ra 6gl ra/gl ra3Calculate the frequency of recombination between these genes.4.13 The recessive alleles b and cn of two genes in chromosome 2 of Drosophila determine black body color andcinnabar eye color, respectively.
If the genes are 8 map units apart, what are the expected genotypes andphenotypes and their relative frequencies among the progeny of the cross + +/b cn × + +/b cn? (Remember thatcrossing-over does not occur in Drosophila males.)4.14 In a testcross of an individual heterozygous for each of three linked genes, the most frequent classes ofprogeny were A B c/a b c and a b C/a b c, and the least frequent classes were A B C/a b c and a b c/a b c. What wasthe genotype of the triple heterozygote parent, and what is the order of the genes?4.15 Construct a map of a chromosome from the following recombination frequencies between individual pairs ofgenes: r—c, 10; c—p, 12; p—r, 3; s—c, 16; s—r, 8. You will discover that the distances are not strictly additive.Why aren't they?4.16 Yellow versus gray body color in D.
melanogaster is determined by the alleles y and y+, vermilion versuswildtype eyes by the alleles v and v+, and singed versus straight bristles by the alleles sn and sn+. When femalesheterozygous for each of these X-linked genes were testcrossed with yellow, vermilion, singed males, thefollowing classes and numbers of progeny were obtained:yellow, vermilion, singedyellow, vermilion53108yellow, singed331yellow5vermilion, singed3vermilion342singed95wildtype63(a) What is the order of the three genes? Construct a linkage map with the genes in their correct order, and indicatethe map distances between the genes.(b) How does the frequency of double crossovers observed in this experiment compare with the frequencyexpected if crossing-over occurs independently in the two chromosome regions? Determine the coefficient ofcoincidence and the interference.4.17 In corn, the alleles C and c result in colored versus colorless seeds, Wx and wx in nonwaxy versus waxyendosperm, and Sh and sh in plump versus shrunken endosperm.
When plants grown from seeds heterozygous foreach of these pairs of alleles were testcrossed with plants from colorless, waxy, shrunken seeds, the progeny seedswere as follows:Colorless, nonwaxy, shrunken84colorless, nonwaxy, plump974colorless, waxy, shrunken20colorless, waxy, plump2349colored, waxy, shrunken951colored, waxy, plumpcolored, nonwaxy, shrunkencolored, nonwaxy, plumpTotal992216156708Determine the order of the three genes, and construct a linkage map showing the genetic distances betweenadjacent genes.Page 1694.18 The accompanying diagram summarizes the recombination frequencies observed in a large experiment tostudy three linked genes.What was the observed frequency of double crossing-over in this experiment? Calculate the interference.4.19 The recessive mutations b (black body color), st (scarlet eye color), and hk (hooked bristles) identify threeautosomal genes in D.
melanogaster. The following progeny were obtained from a testcross of femalesheterozygous for all three genes.black, scarlet243black241black, hooked15black, hooked, scarlet10hooked235hooked, scarlet226scarlet12wildtype18What conclusions are possible concerning the linkage relations of these three genes? Calculate any appropriate mapdistances.4.20 In the nematode Caenorhabditis elegans, the mutations dpy-21 (dumpy) and unc-34 (uncoordinated) identifylinked genes that affect body conformation and coordination of movement. The frequency of recombinationbetween the genes is 24 percent. If the heterozygote dpy-21 +/+ unc-34 undergoes self-fertilization (the normalmode of reproduction in this organism), what fraction of the progeny is expected to be both dumpy anduncoordinated?4.21 Dark eye color in rats requires the presence of a dominant allele of each of two genes, R and P.
Animalshomozygous for either or both of the recessive alleles have light-colored eyes. In one experiment, homozygousdark-eyed rats were crossed with doubly recessive light-eyed rats, and the resulting F1 animals were testcrossedwith rats of the homozygous light-eyed strain. The progeny from the test-cross consisted of 628 dark-eyed and 889light-eyed rats. In another experiment, R p R p animals were crossed with r P r P animals, and the F1 progeny werecrossed with animals from an r p r p strain.
The progeny consisted of 86 dark-eyed and 771 light-eyed rats.Determine whether the genes are linked, and if they are, estimate the frequency of recombination between thegenes from each of the experiments.4.22 A Drosophila geneticist exposes flies to a mutagenic chemical and obtains nine mutations nine mutations inthe X chromosome that are lethal when homozygous. The mutations are tested in pairs in complementation tests,with the results shown in the accompanying table.
A + indicates complementation (that is, flies carrying bothmutations survive), and a - indicates noncomplementation (flies carrying both mutations die). How many genes(complementation groups) are represented by the mutations, and which mutations belong to each complementationgroup?1123456789-+-+++-++-+++++++-+++-++-+-+++-+++--+++-++-+23456789-4.23 The following classes and frequencies of ordered tetrads were obtained from the cross a+ b+ × a b inNeurospora.
(Only one member of each pair of spores is shown.)Spore pairNumberof asci1–23–45–67–8a+b+a +b +abab1766a+b+aba+b+ab220a+b+ab+a+ban14What is the order of the genes in relation to the centromere?4.24 Three genes in chromosome 9 of corn determine shrunken sh versus plump Sh kernels, waxy wx versusnonwaxy Wx endosperm, and glossy gl versus nonglossy Gl leaves.
The genetic map of this chromosomal region issh—30—wx—10—gl. From a plant of genotype Sh wx Gl/sh Wx gl, what is the expected frequency of sh wx glgametes:(a) in the absence of interference?(b) assuming 60 percent interference?4.25 The following spore arrangements were obtained in the indicated frequencies from ordered tetrads in a crossbetween a Neurospora strain com val (c v), which exhibits a compact growth form and is unable to synthesize theamino acidPage 170valine, and a wildtype strain, + +.
(Only one member of each pair of spores is shown.)Spore pairAccus composition1–2cvc+cv+vcv3–4cvc+c+c++v5–6+++v+vcvc+7–8+++v++++++Number:34362019What can you conclude about the linkage and location of the genes with respect to each other and to thecentromere?Challenge Problems4.26 In Neurospora several genes are needed for production of black pigment in spores. Recessive alleles at anyone of these can result in tan spores. Six possible arrangements of spore colors are possible in crosses segregatingfor one of these allelic pairs, as shown in the accompanying diagram.
Three different allelic pairs were analyzed incrosses 1, 2, and 3, respectively. The results are tabulated in the illustration.For each cross, indicate how the different arrangements arise and what you can deduce about the location of thesegregating gene. In crosses in which it is relevant, calculate a map distance.4.27 In baker's yeast (Saccharomyces cerevisiae), which produces unordered asci, the following cross was made:The resulting diploid was induced to undergo meiosis, and the asci were dissected and spore clones analyzed. Thefollowing tetrad types were found, with the observed number of each shown below. For convenience, leu2, trp1,and met14 are abbreviated l, t, and m, respectively.Analyze these data as fully as you can with respect to the linkage of each gene with respect to every other gene andwith respect to its centromere.
Where a genetic linkage is indicated, calculate the map distance.4.28 In baker's yeast (Saccharomyces cerevisiae), which produces unordered asci, the following cross was made:The resulting diploid was induced to undergo meiosis, the asci were dissected, and the spore clones analyzed. Thefollowing tetrad types were found in the numbers shown below each tetrad. For convenience, rad6, trp5, leu1, andmet14 are abbreviated as r, t, l, and m, respectively.Use what you learned about met14 in Challenge Problem 4.27 to analyze these data as fully as you can for linkageof the genes to one another and of each to its respective centromere. When genetic linkage is indicated, calculatethe map distance.Page 171Further ReadingBotstein, D., R. L.
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