Page 182 - Genetics_From_Genes_to_Genomes_6th_FULL_Part1

174 Chapter 5 Linkage, Recombination, and the Mapping of Genes on Chromosomes

21. Map distances were determined for four different Parental cross Testcross offspring of F 1 females
genes (MAT, HIS4, THR4, and LEU2) on chromo- mb mb , e e × normal bristles, normal body 117
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some III of the yeast Saccharomyces cerevisiae: mb mb, e e normal bristles, ebony body 11
missing bristles, normal body 15
HIS4 ↔ MAT 37 cM missing bristles, ebony body 107
THR4 ↔ LEU2 35 cM + + + +
LEU2 ↔ HIS4 23 cM k k , e e × k k, e e normal eyes, normal body 11
MAT ↔ LEU2 16 cM normal eyes, ebony body 150
MAT ↔ THR4 20 cM kidney eyes, normal body 144
kidney eyes, ebony body 7
What is the order of genes on the chromosome? mb mb , k k × normal bristles, normal eyes 203
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22. In the tubular flowers of foxgloves, wild-type mb mb, k k normal bristles, kidney eyes 11
coloration is red while a mutation called white missing bristles, normal eyes 15
produces white flowers. Another mutation, called missing bristles, kidney eyes 193
peloria, causes the flowers at the apex of the stem
to be huge. Yet another mutation, called dwarf, 24. A snapdragon with pink petals, black anthers, and long
affects stem length. You cross a white-flowered stems was allowed to self-fertilize. From the resulting
plant (otherwise phenotypically wild type) to a seeds, 650 adult plants were obtained. The phenotypes
plant that is dwarf and peloria but has wild-type of these offspring are listed here.
red flower color. All of the F 1 plants are tall with
white, normal-sized flowers. You cross an F 1 plant 78 red long tan
back to the dwarf and peloria parent, and you see 26 red short tan
the 543 progeny shown in the chart. (Only mutant 44 red long black
traits are noted.) 15 red short black
39 pink long tan
dwarf, peloria 172 13 pink short tan
white 162 204 pink long black
dwarf, peloria, white 56 68 pink short black
wild type 48 5 white long tan
dwarf, white 51 2 white short tan
peloria 43 117 white long black
dwarf 6 39 white short black
peloria, white 5
a. Which alleles are dominant? a. Using P for one allele and p for the other, indicate
how flower color is inherited.
b. What were the genotypes of the parents in the orig-
inal cross? b. What numbers of red : pink : white would have
been expected among these 650 plants?
c. Draw a map showing the linkage relationships of
these three loci. c. How are anther color and stem length inherited?
d. Do the data provide evidence for interference? If d. What was the genotype of the original plant?
so, calculate the coefficient of coincidence and the e. Do any of the three genes show independent
interference value. assortment?
23. In Drosophila, the recessive allele mb of one gene f. For any genes that are linked, indicate the arrange-
causes missing bristles, the recessive allele e of a ments of the alleles on the homologous chromo-
second gene causes ebony body color, and the recessive somes in the original snapdragon, and estimate the
allele k of a third gene causes kidney-shaped eyes. distance between the genes.
(Dominant wild-type alleles of all three genes are 25. In Drosophila, three autosomal genes have the follow-
indicated with a + superscript.) The three different ing map:
P generation crosses in the table that follows were
conducted, and then the resultant F 1 females from a b c
each cross were testcrossed to males that were 20 m.u. 10 m.u.
homozygous for the recessive alleles of both genes
in question. The phenotypes of the testcross offspring a. Provide the data, in terms of the expected number
are tabulated. Determine the best genetic map explaining of flies in the following phenotypic classes, when
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all the data. a b c / a b c females are crossed to a b c / a b c