. An allotetraploid species has a genome composed oftwo ancestral genomes, A and B, each of which havea basic chromosome number (x) of seven. In thisspecies, the two copies of each chromosome of eachancestral genome pair only with each other duringmeiosis. Resistance to a pathogen that attacks the foliage of the plant is controlled by a dominant allele atthe F locus. The recessive alleles Faand Fbconfersensitivity to the pathogen, but the dominant resistancealleles present in the two genomes have slightly different effects. Plants with at least one FAallele areresistant to races 1 and 2 of the pathogen regardlessof the genotype in the B genome, and plants with atleast one FBallele are resistant to races 1 and 3 of thepathogen regardless of the genotype in the A genome.What proportion of the self-progeny of an FA Fa FB Fbplant will be resistant to all three races of the pathogen?

. An allotetraploid species has a genome composed oftwo ancestral genomes, A and B, each of which havea basic chromosome number (x) of seven. In thisspecies, the two copies of each chromosome of eachancestral genome pair only with each other duringmeiosis. Resistance to a pathogen that attacks the foliage of the plant is controlled by a dominant allele atthe F locus. The recessive alleles Faand Fbconfersensitivity to the pathogen, but the dominant resistancealleles present in the two genomes have slightly different effects. Plants with at least one FAallele areresistant to races 1 and 2 of the pathogen regardlessof the genotype in the B genome, and plants with atleast one FBallele are resistant to races 1 and 3 of thepathogen regardless of the genotype in the A genome.What proportion of the self-progeny of an FA Fa FB Fbplant will be resistant to all three races of the pathogen?

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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On rare occasions, an organism may have three copies of achromosome and therefore has three copies of the genes on thatchromosome (instead of the usual number of two copies). Forsuch a rare organism, the alleles for each gene usually segregateso that a gamete will contain one or two copies of the gene. Let’ssuppose that a rare pea plant has three copies of the chromosomethat carries the height gene. Its genotype is TTt. The plant is alsoheterozygous for the seed color gene, Yy, which is found on adifferent chromosome. With regard to both genes, how manytypes of gametes can this plant make, and in what proportions?(Assume that it is equally likely that a gamete will contain oneor two copies of the height gene.)
The Drosophila chromosome 4 is extremely small;virtually no recombination occurs between genes onthis chromosome. You have available three differentlymarked chromosome 4s: one has a recessive allele ofthe gene eyeless (ey), causing very small eyes; one hasa recessive allele of the cubitus interruptus (ci) gene,which causes disruptions in the veins on the wings;and the third carries recessive alleles of both genes.Drosophila adults can survive with two or three, butnot with one or four, copies of chromosome 4.a. How could you use these three chromosomes tofind Drosophila mutants with defective meiosescausing an elevated rate of nondisjunction?b. Would your technique allow you to discriminatenondisjunction occurring during the first meioticdivision from nondisjunction occurring during thesecond meiotic division?
The Drosophila chromosome 4 is extremely small;virtually no recombination occurs between genes onthis chromosome. You have available three differentlymarked chromosome 4s: one has a recessive allele ofthe gene eyeless (ey), causing very small eyes; one hasa recessive allele of the cubitus interruptus (ci) gene,which causes disruptions in the veins on the wings;and the third carries recessive alleles of both genes.Drosophila adults can survive with two or three, butnot with one or four, copies of chromosome 4.a. How could you use these three chromosomes tofind Drosophila mutants with defective meiosescausing an elevated rate of nondisjunction?b. Would your technique allow you to discriminatenondisjunction occurring during the first meioticdivision from nondisjunction occurring during thesecond meiotic division?c. What progeny types would you expect if a flyrecognizably formed from a gamete produced bynondisjunction were testcrossed to a fly homozygous for a chromosome 4 carrying both ey…
. A diploid strain of yeast was made by mating a haploidstrain with a genotype w−, x−, y−, and z− with a haploidstrain of opposite mating type that is wild type for thesefour genes. The diploid strain was phenotypically wildtype. Four different X-ray-induced diploid mutantswith the following phenotypes were produced fromthis diploid yeast strain. Assume a single new mutation is present in each strain.Strain 1 w− x+ y− z+Strain 2 w+ x− y− z−Strain 3 w− x+ y− z−Strain 4 w− x+ y+ z+When these mutant diploid strains of yeast go throughmeiosis, each ascus is found to contain only two viablehaploid spores.a. What kind of mutations were induced by X-rays tomake the listed diploid strains?b. Why did two spores in each ascus die?c. Are any of the genes w, x, y, or z located on thesame chromosome?d. Give the order of the genes that are found on thesame chromosome
The maternal-effect mutation bicoid (bcd) is recessive. Inthe absence of the bicoid protein product, embryogenesis isnot completed. Consider a cross between a female heterozygousfor the bicoid mutation (bcd+/ bcd-) and a homozygousmale(bcd-/ bcd-). Predict the outcome (normal vs. failed embryogenesis) inthe F1 and F2 generations of the cross described.
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?
In Drosophila, a cross (cross 1) was made between twomutant flies, one homozygous for the recessive mutationbent wing (b) and the other homozygous for the recessivemutation eyeless (e). The mutations e and b are alleles oftwo different genes that are known to be very closelylinked on the tiny autosomal chromosome 4. All the progeny had a wild-type phenotype. One of the female progeny was crossed with a male of genotype b e/b e ; we willcall this cross 2. Most of the progeny of cross 2 were of theexpected types, but there was also one rare female ofwild-type phenotype.a. Explain what the common progeny are expected tobe from cross 2.b. Could the rare wild-type female have arisen by (1)crossing over or (2) nondisjunction? Explain.
During ascus formation in Neurospora, any ascosporewith a chromosomal deletion dies and appears whitein color. How many of the eight ascospores in theascus would be white if the octad came from a crossof a wild-type strain with a strain of the oppositemating type carrying:a. a paracentric inversion, and no crossovers occurredbetween normal and inverted chromosomes?b. a pericentric inversion, and a single crossoveroccurred in the inversion loop?c. a paracentric inversion, and a single crossoveroccurred outside the inversion loop?d. a reciprocal translocation, and an adjacent-1segregation occurred with no crossovers betweentranslocated chromosomes?e. a reciprocal translocation, and alternate segregationoccurred with no crossovers between translocatedchromosomes?f. a reciprocal translocation, and alternate segregation occurred with one crossover between translocated chromosomes (but not between thetranslocation breakpoint and the centromereof any chromosome)?
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.”
The following corn loci are on one arm of chromosome9 in the order indicated (the distances between themare shown in map units):c-bz-wx-sh-d-centromere12 8 10 20 10C gives colored aleurone; c, white aleurone.Bz gives green leaves; bz, bronze leaves.Wx gives starchy seeds; wx, waxy seeds.Sh gives smooth seeds; sh, shrunken seeds.D gives tall plants; d, dwarf.A plant from a standard stock that is homozygous for allfive recessive alleles is crossed with a wild-type plantfrom Mexico that is homozygous for all five dominantalleles. The F1 plants express all the dominant allelesand, when backcrossed to the recessive parent, give thefollowing progeny phenotypes:colored, green, starchy, smooth, tall 360white, bronze, waxy, shrunk, dwarf 355colored, bronze, waxy, shrunk, dwarf 40white, green, starchy, smooth, tall 46colored, green, starchy, smooth, dwarf 85white, bronze, waxy, shrunk, tall 84colored, bronze, waxy, shrunk, tall 8white, green, starchy, smooth, dwarf 9colored, green, waxy, smooth,…
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?
Drosophila P elements were discovered because ofa phenomenon called hybrid dysgenesis—sterilityof particular hybrid progeny. When scientists in the1970s crossed their D. melanogaster laboratorystrains to flies of the same species obtained fromnatural environments outside the lab, they observeda remarkable result: The progeny of the crosseswere sterile, but only when outside males werecrossed with lab strain females. Progeny resultingfrom crosses of outside females with lab maleswere perfectly normal.DNA analysis revealed that while the genomesof the outside flies contain P elements, the lab flygenomes have none. Apparently, P elements spreadthroughout the wild population of D. melanogasterafter the capture of the originators of present-daylaboratory strains over 100 years ago.a. The hybrid progeny are sterile because their germline cells have a high rate of mutation and chromosomal rearrangement (dysgenesis) caused by highrates of P element mobilization. Explain howP element movement…