Researchers have discovered that some regions of chromosomesare much more likely than others to cross over. We might callsuch a region a “hot spot” for crossing over. Let’s suppose thattwo genes, gene A and gene B, are 5,000,000 bp apart on thesame chromosome. Genes A and B are in a hot spot for crossingover. Two other genes, let’s call them gene C and gene D, are also5,000,000 bp apart but are not in a hot spot for crossing over. Ifwe conducted two-factor crosses to compute the map distancebetween genes A and B and other two-factor crosses to compute themap distance between genes C and D, would the calculated mapdistance between A and B be the same as that between C and D? Explain.

Researchers have discovered that some regions of chromosomesare much more likely than others to cross over. We might callsuch a region a “hot spot” for crossing over. Let’s suppose thattwo genes, gene A and gene B, are 5,000,000 bp apart on thesame chromosome. Genes A and B are in a hot spot for crossingover. Two other genes, let’s call them gene C and gene D, are also5,000,000 bp apart but are not in a hot spot for crossing over. Ifwe conducted two-factor crosses to compute the map distancebetween genes A and B and other two-factor crosses to compute themap distance between genes C and D, would the calculated mapdistance between A and B be the same as that between C and D? Explain.

Human Heredity: Principles and Issues (MindTap Course List)

11th Edition

ISBN:9781305251052

Author:Michael Cummings

Publisher:Michael Cummings

Chapter6: Cytogenetics: Karyotypes And Chromosome Aberrations

Section: Chapter Questions

Problem 3QP: A colleague e-mails you saying that she has identified an interesting chromosome variation at 21q13....

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Similar questions

. In ordered tetrad analysis, what is the maximumRF that you could observe between a gene and thecentromere? (Hint: What RF would you observebetween a gene and the centromere if the genewere distant enough from the centromere so thatat least one crossover, and often more than onecrossover, occurs between them in everymeiosis?)b. Can a gene and the centromere be unlinked?Explain.c. Suppose in an ordered tetrad analysis you observean RF of 30% between a gene and the centromere.Given your answer to part (a), do think that 30 m.u.is an accurate estimate of the distance between thegene and the centromere?
The karyotype of a young girl who is affected with familialDown syndrome revealed a total of 46 chromosomes. Her olderbrother, however, who is phenotypically unaffected, actually had45 chromosomes. Explain how this could happen. What wouldyou expect to be the numbers of chromosomes in the parents ofthese two children?
Fathers contribute more new point mutations to theirchildren than mothers. You may know from general biology that people have sex chromosomes—two X chromosomes in females and an X plus a Y chromosome inmales. Both sexes have the autosomes (A’s).a. On which type of chromosome (A, X, or Y) wouldyou expect the genes to have the greatest number ofnew mutations per base pair over many generations ina population? Why?b. On which type of chromosome would you expect theleast number of new mutations per base pair? Why?c. Can you calculate the expected number of newmutations per base pair for a gene on the X and Ychromosomes for every one new mutation in a geneon an autosome if the mutation rate in males is twicethat in females?
EVOLUTION CONNECTION Crossing over is thought to beevolutionarily advantageous because it continually shufflesgenetic alleles into novel combinations. Until recently, it wasthought that the genes on the Y chromosome might degenerate because they lack homologous genes on the X chromosomewith which to pair up prior to crossing over. However, when theY chromosome was sequenced, eight large regions were foundto be internally homologous to each other, and quite a few ofthe 78 genes represent duplicates. (Y chromosome researcherDavid Page has called it a “hall of mirrors.”) Explain what mightbe a benefit of these regions.
While conducting field studies on a chain of islands, you decide tokaryotype two phenotypically identical groups of turtles, which arefound on different islands. The turtles on one island have 24 chromosomes,but those on another island have 48 chromosomes. Howwould you explain this observation? How do you think the turtleswith 48 chromosomes came into being? If you crossed the twotypes of turtles, would you expect the offspring to be phenotypicallynormal? Would you expect them to be fertile? Explain.
A cytogeneticist has collected tissue samples from members of acertain butterfly species. Some of the butterflies were located inCanada, and others were found in Mexico. Through karyotyping,the cytogeneticist discovered that chromosome 5 of the Canadianbutterflies had a large inversion compared with chromosome 5 ofthe Mexican butterflies. The Canadian butterflies were inversionhomozygotes, whereas the Mexican butterflies had two normalcopies of chromosome 5.Explain whether a mating between Canadian and Mexicanbutterflies would produce phenotypically normal offspring?
DRAW IT Suppose, as in the questionat the bottom of Figure 15.9, the parental(P generation) flies were true-breedingfor gray body with vestigial wings andblack body with normal wings. Draw thechromosomes in each of the four possiblekinds of eggs from an F1 female, andlabel each chromosome as “parental”or “recombinant.”
A crossover has occurred in the bivalent shown in figure.What is the outcome of this single crossover event? If a secondcrossover occurs somewhere between A and C, explain which twochromatids it would involve and where it would occur (i.e., betweenwhich two genes) to produce the chromosomes shown here:A. ABC, AbC, aBc, and abcB. Abc, Abc, aBC, and aBCC. ABc, Abc, aBC, and abCD. ABC, ABC, abc, and abc
Why is a chromosome with two centromeres (adicentric chromosome) unstable? Would a backup cen-tromere not be a good thing for a chromosome, giving ittwo chances to form a kinetochore and attach to microtu-bules during mitosis? Would that not help to ensure thatthe chromosome did not get left behind at mitosis?
. Chromosome 3 of corn carries three loci (b for plant-color booster, v for virescent, and lg for liguleless). A testcross of triple recessives with F1 plants heterozygous forthe three genes yields progeny having the followinggenotypes: 305 + v lg, 275 b + +, 128 b + lg, 112 + v +,74 + + lg, 66 b v +, 22 + + +, and 18 b v lg. Give the genesequence on the chromosome, the map distances between genes, and the coefficient of coincidence.
why The chromatids formedby recombination within the inversion loop of a paracentric inversionheterozygote containtwo centromeres or none, instead of the normal one ?
In the experiment of Figure shown, Stern followed the inheritancepattern in which females carried two abnormal X chromosomesto correlate genetic recombination with the physical exchange ofchromosome pieces. Is it necessary to use a strain carrying twoabnormal chromosomes, or could he have used a strain in whichfemales carried one normal X chromosome and one abnormal Xchromosome with a deletion at one end and an extra piece of the Ychromosome at the other end?