Contact G. Maroni Contact: Adam Cheely Lewei Duan Chevonne Eversley
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Contact G. Maroni Contact: Adam Cheely Lewei Duan Chevonne Eversley
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Problems
1) As Mendel discovered, gray seed color in peas is dominant to white. In the following experiments, parents with known phenotypes but unknown genotypes produced the listed progeny:
Using the letter G for the gray gene and g for white, give the most probable genotype of each parent.
2) Groff and Odland found a variety of cucumber whose flowers failed to open when mature. These flowers failed to open when mature. These flowers could nevertheless be pollinated by opening them artificially. The results of their experiments were:
3)
Define symbols for the genes involved and indicate the genotypes of: (a) The closed parents. (b) The open parents. (c) The F1.
4) In dogs dark coat color is dominant over albino, and short hair is dominant over long hair. If these effects are caused by two independently segregating gene pairs, write the most probable genotypes for the parents of each of the following crosses, using the symbols C and c for the dark and albino coat-color alleles, and S and s for the short-and long-hair alleles, respectively.
5) In Drosophila melanogaster one gene pair is known to affect wing size, and the allele for normal long wings (vg+) in this gene pair has a dominant effect over the allele for short vestigial wings (vg). Another independently assorting gene pair affects body color: The allele for normal grey body color (e+) is dominant to that for ebony body color (e). A cross is made between a fly with normal wings and ebony body color and a fly with vestigial wings and normal body color. The normal-appearing F1 are crossed among each other and 512 F2 flies are raised. What phenotypes would you expect in the F2 and in what numbers would you expect to find them?
6) In corn a pair of genes determines leaf shape and another pair determines pollen shape. A ragged-leafed plant with round-pollen was crossed to a ragged-leafed plant with angular-pollen , and the resultant progeny were classified as follows:
Class 1: 186 ragged-leaf round-pollen Class 2: 174 ragged-leaf angular-pollen Class 3: 57 smooth-leaf round-pollen Class 4: 63 smooth-leaf angular-pollen Total 480
(a) Using alphabetical letters of your choice, designate the genes for the different leaf and pollen characters. (b) On the basis of the symbols given in (a), provide genotypes for the two parents. (c) According to your hypothesis what numbers would you have expected for each of the four classes of progeny? (d) Test your hypothesis statistically using the chi-square method (Chapter 8) and indicate whether you accept or reject your hypothesis.
7) In foxes a platinum mutation arose in Norway in 1933 that appeared to be a dominant allele of the silver gene. The platinum mutant was then mated to silver animals to obtain an F1. About 50 matings were than made between F1 platinum and F1 platinum which produced an F2 of about 100 platinum foxes and 50 silver. How can this ration be explained?
8) Among the various coat colors in mice, there may be yellow, agouti, or black. Crosses made between certain mice provided the following results: Parents
F1 offspring cross 1 yellow x yellow 2/3 yellow: 1/3 agouti cross 2 yellow x agouti 1/2 yellow: 1/2 agouti cross 3 yellow x black 1/2 yellow: 1/2 black cross 4 black x agouti all agouti
What phenotypic ratios would you expect from the following crosses: (a) F1 yellow (cross 1) x F1 yellow (cross 2)? (b) F1 agouti (cross 4) x F1 yellow (cross 2)? (c) F1 agouti (cross 4) x F1 yellow (cross 3)?
9) Abnormal eye shape in Drosophila may be caused by a variety of mutant genes, dominant or recessive, sex-linked or autosomal. One normal-eyed Drosophila melanogaster male from a true-breeding normal stock was crossed to two different abnormal-eyed females with the following results:
Progeny of
Progeny of female 1 female 2 ♀ ♂ ♀ ♂ normal-eyed 108 0 51 49 abnormal-eyed 0 102 53 50
10) In corn the seeds can be colored or white, nonshrunken or shrunken. Each of these characteristics is determined by a separate pair of genes, C and c and Sh and sh. Hutchison crossed a homozygous colored shrunken strain (CC shsh) to a homozygous white non- shrunken strain (ccShSh) and obtained a heterozygous colored nonshrunken F1. The F1 was backcrossed to a homozygous recessive white shrunken stock and the progeny were as follows:
No. plants
colored shrunken 21,379 white nonshrunken 21,096 colored nonshrunken 638 white shrunken 672 What is the recombination frequency between these two genes?
11) Can you distinguish between two gene loci located on the same chromosome that have 50 percent crossing over between them and two gene loci each located on different nonhomologous chromosomes? Explan.
12) In the tomato the mutant genes o (oblate = flattened fruit), p (peach = hairy fruit), and s (com-pound inflorescence = many flowers in a cluster) were found to be in chromosome 2. From the following data (testcross mating of an F1 heterozygote for all three genes x homozygous recessive for all three genes) determine: (a) The sequence of these three genes in chromosome 2. (b) The genotypes of the homozygous parents used in making the F1 heterozygote. (c) The recombination distances between the genes. (d) The coefficient of coincidence.
Phenotypes of testcross progeny Number + + + 73 + + s 348 + p + 2 + p s 96 o + + 110 o + s 2 o p + 306 o p s 63
13) In corn three gene pairs linked on the same chromosome are those for plant color, in which yellow (y) is recessive to green (Y); endosperm shape, in which shrunken (sh) is recessive to full (Sh); and seed color, in which colorless (c) is recessive to colored (C). Three different plants, I, II, and III, each heterozygous for these three gene loci, although not necessarily heterozygous in the same fashion as the others (i.e., y sh c/Y Sh C, Y Sh c/y sh C, etc.), were backcrossed to homozygous triple recessives, y sh c / y sh c, and produced progeny which had the following phenotypic frequencies:
(a) Using the progeny from any one of the heterozygous plants, propose the gene order and the recombination distances between the three genes. (b) On the basis of (a)——, compute the coefficient of coincidence. (c) For the plant analyzed in (a) and (b), describe the frequency changes you would expect among its progeny if interference were increased. (d) Give the exact genotypes for each of the two homologous chromosomes bearing the three genes in heterozygous plants, I, II, and III.
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