Page 184 - Genetics_From_Genes_to_Genomes_6th_FULL_Part1

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

31. The following list of four Drosophila mutations indi- primary spermatocytes, these researchers isolated and
cates the symbol for the mutation, the name of the then sequenced the DNA of individual chromosomes
gene, and the mutant phenotype: from the man’s somatic cells. However, although this
last step provided useful confirmation,
Allele symbol Gene name Mutant phenotype it was not actually essential for determining the
dwp dwarp small body, warped wings two DNA sequences for each chromosome the man
rmp rumpled deranged bristles inherited, one from his mother and one from his
pld pallid pale wings father. Instead, as you will demonstrate, this informa-
rv raven dark eyes and bodies tion can be inferred from the DNA sequences of the
You perform the following crosses with the indicated ~100 single sperm.
results: a. Diagram three syntenic autosomal SNP loci for
which the man is heterozygous, and suppose that
Cross #1: dwarp, rumpled females × pallid, raven males the middle SNP locus is separated from each of
→ dwarp, rumpled males and wild-type females those flanking it by 25 m.u. Use alleles of your
Cross #2: pallid, raven females × dwarp, rumpled males choice for each of the three loci in your diagram.
→ pallid, raven males and wild-type females
b. For simplicity, assume that interference = 1. Now,
F 1 females from cross #1 were crossed to males from accounting only for these three loci, how many
a true-breeding dwarp rumpled pallid raven stock. different types of sperm would you see, and in
The 1000 progeny obtained were as follows: what frequencies?
c. Given the results shown in the Fast Forward Box,
pallid 3 explain why the assumption that interference = 1
pallid, raven 428 is reasonable in this case.
pallid, raven, rumpled 48
pallid, rumpled 23 d. Explain how you would design a computer
dwarp, raven 22 program that could reconstruct the DNA sequences
dwarp, raven, rumpled 2 of each chromosome in the somatic cells of a man,
dwarp, rumpled 427 given the DNA sequences of 100 single sperm
dwarp 47 he produces.
Indicate the best map for these four genes, including
all relevant data. Calculate interference values where Section 5.4
appropriate. 35. Do the data that Mendel obtained fit his hypotheses?
32. a. Explain in a qualitative sense how Fig. 5.7a For example, Mendel obtained 315 yellow round, 101
suggests the existence of interference along yellow wrinkled, 108 green round, and 32 green
mouse chromosomes. wrinkled seeds from the selfing of Yy Rr individuals
b. If you could examine many photographs similar to (a total of 556). His hypotheses of segregation and
Fig. 5.7a, how would you apply statistics to provide independent assortment predict a 9:3:3:1 ratio in this
evidence for the existence of interference during case. Use the chi-square test to determine whether
meiosis in mice? (No equations required; just Mendel’s data are significantly different from what
outline the logic involved.) he predicted. (The chi-square test did not exist in
33. The total length of the mouse genetic map is 1386 cM Mendel’s day, so he was not able to test his own data
for goodness of fit to his hypotheses.)
measured in males but 1817 cM measured in females.
If Fig. 5.7a on shows a prophase I representative of all 36. Two genes control color in corn snakes as follows:
primary spermatocytes, how many recombination O– B– snakes are brown, O– bb are orange, oo B– are
nodules would you expect to find in a representative black, and oo bb are albino. An orange snake was
prophase I primary oocyte? mated to a black snake, and a large number of F 1
progeny were obtained, all of which were brown.
34. The Fast Forward Box Mapping the Crossovers When the F 1 snakes were mated to one another, they
that Generate the Chromosomes of Individual produced 100 brown offspring, 25 orange, 22 black,
Human Sperm describes how scientists used the and 13 albino.
whole genome DNA sequencing of ~100 single
sperm from the same man to locate the crossovers a. What are the genotypes of the F 1 snakes?
involved in the production of each of these sperm. To b. What proportions of the different colors would
determine the sequences of the parental chromosomes have been expected among the F 2 snakes if the two
between which recombination occurred in the man’s loci assort independently?