Recessive maternal effect genes are identified in flies (for example)when a phenotypically normal mother cannot produce any normaloffspring. Because all of the offspring are dead, this female fly cannot be used to produce a strain of heterozygous flies that could beused in future studies. How would you identify heterozygous individuals that are carrying a recessive maternal effect allele? Howwould you maintain this strain of flies in a laboratory over manygenerations?
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Recessive maternal effect genes are identified in flies (for example)
when a
offspring. Because all of the offspring are dead, this female fly cannot be used to produce a strain of heterozygous flies that could be
used in future studies. How would you identify heterozygous individuals that are carrying a recessive maternal effect allele? How
would you maintain this strain of flies in a laboratory over many
generations?
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- . In 1919, Calvin Bridges began studying an X-linkedrecessive mutation causing eosin-colored eyes inDrosophila. Within an otherwise true-breedingculture of eosin-eyed flies, he noticed rare variantsthat had much lighter cream-colored eyes. By intercrossing these variants, he was able to make a truebreeding cream-eyed stock. Bridges now crossedmales from this cream-eyed stock with true-breedingwild-type females. All the F1 progeny had red (wildtype) eyes. When F1 flies were intercrossed, the F2progeny were 104 females with red eyes, 52 maleswith red eyes, 44 males with eosin eyes, and14 males with cream eyes. Assume that thesenumbers represent an 8:4:3:1 ratio.a. Formulate a hypothesis to explain the F1 and F2results, assigning phenotypes to all possiblegenotypes.b. What do you predict in the F1 and F2 generations if the parental cross is between truebreeding eosin-eyed males and true-breedingcream-eyed females?c. What do you predict in the F1 and F2 generationsif the parental cross is…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?Let’s suppose that you have made a karyotype of a female fruit flywith red eyes and found that it has three X chromosomes insteadof the normal two. Although you do not know its parents, you doknow that this fly came from a mixed culture of flies in whichsome had red eyes, some had white eyes, and some had eosin eyes.Eosin is an allele of the same gene that has white and red alleles.Eosin is a pale orange color. The red allele is dominant and thewhite allele is recessive. The expression of the eosin allele, however, depends on the number of copies of the allele. When femaleshave two copies of this allele, they have eosin eyes. When femalesare heterozygous for the eosin allele and the white allele, they havelight-eosin eyes. When females are heterozygous for the red alleleand the eosin allele, they have red eyes. Males that have a singlecopy of the eosin allele have eosin eyes.You cross the XXX red-eyed female with a white-eyed male andcount the numbers of offspring. You may assume that…
- In individuals affected by cystic fibrosis, salt crystals may appear afterperspiration dries up. In addition, the disease causes respiratory disorderswhich can be both debilitating and lethal. It occurs in individuals homozygousfor the recessive gene. Two normal parents had a daughter with thesymptoms of this disease, and a normal son who marries a normal womanwith an afflicted A test (salt concentration in perspiration of heterozygotes ishigher than normal) disclosed that both are indeed carriers of the gene. If thefirst child born to the mating in (b) was defective, what is the probability thatthe 2nd child would also be defective?Express answer in fraction formThe following list of four Drosophila mutations indicates the symbol for the mutation, the name of thegene, and the mutant phenotype:Allele symbol Gene name Mutant phenotypedwp dwarp small body, warped wingsrmp rumpled deranged bristlespld pallid pale wingsrv raven dark eyes and bodiesYou perform the following crosses with the indicatedresults:Cross #1: dwarp, rumpled females × pallid, raven males→ dwarp, rumpled males and wild-type femalesCross #2: pallid, raven females × dwarp, rumpled males→ pallid, raven males and wild-type femalesF1 females from cross #1 were crossed to males froma true-breeding dwarp rumpled pallid raven stock.The 1000 progeny obtained were as follows:pallid 3pallid, raven 428pallid, raven, rumpled 48pallid, rumpled 23dwarp, raven 22dwarp, raven, rumpled 2dwarp, rumpled 427dwarp 47Indicate the best map for these four genes, includingall relevant data. Calculate interference values whereappropriate.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…In Drosophila, a heterozygous female for the X-linkedrecessive traits a, b, and c was crossed to a male that phenotypically expressed a, b, and c. The offspring occurred inthe following phenotypic ratios.+ b c 460a + + 450a b c 32+ + + 38a + c 11+ b + 9 No other phenotypes were observed.(a) What progeny phenotypes are missing? Why?A maternal effect gene in Drosophila, called torso, occurs as a functionalallele (torso+) and a nonfunctional, recessive allele (torso−)that prevents the correct development of anterior- and posterior-moststructures. A wild-type male (torso+torso+) is crossed to a female ofunknown genotype. This cross produces offspring (larva) that are allmissing their anterior- and posterior-most structures and therefore die during early development. What are the genotype and the phenotypeof the female fly in this cross? What are the genotypes andphenotypes of the female fly’s parents?
- . 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 chromosomeImagine that you caught a female albino mouse inyour kitchen and decided to keep it for a pet. A fewmonths later, while vacationing in Guam, you caughta male albino mouse and decided to take it home forsome interesting genetic experiments. You wonderwhether the two mice are both albino due to mutations in the same gene. What could you do to find outthe answer to this question? Assume that both mutations are recessive.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…