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.”
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DRAW IT Suppose, as in the question
at the bottom of Figure 15.9, the parental
(P generation) flies were true-breeding
for gray body with vestigial wings and
black body with normal wings. Draw the
chromosomes in each of the four possible
kinds of eggs from an F1 female, and
label each chromosome as “parental”
or “recombinant.”
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- The a, b, and c loci are all on different chromosomesin yeast. When a b+ yeast were crossed to a+ b yeastand the resultant tetrads analyzed, it was found thatthe number of nonparental ditype tetrads was equal tothe number of parental ditypes, but there were no tetratype asci at all. On the other hand, many tetratypeasci were seen in the tetrads formed after a c+ wascrossed with a+ c, and after b c+ was crossed withb+ c. Explain these results.in the experiment of following chromosomal dna mvement througgh meiosis, why. do you use non-sister chromatids to demobstrate crossing over? what combinatiobns of alleles could result from a crossover between BD and bd chromosomes? Identify two ways that meiosis contributes to genetic recombination. Why is it necessary to reduce the number of chromosomes in gametes, but not in other cell?Somatic cells in organisms of a particular diploidplant species normally have 14 chromosomes. Thechromosomes in the gametes are numbered from 1through 7. Rarely, zygotes are formed that containmore or fewer than 14 chromosomes. For each of thezygotes below, (i) state whether the chromosomecomplement is euploid or aneuploid; (ii) provideterms that describe the individual’s genetic makeupas accurately as possible; and (iii) state whether ornot the individual will likely develop through theembryonic stages to make an adult plant, and if so,whether or not this plant will be fertile.a. 11 22 33 44 5 66 77b. 111 22 33 44 555 66 77c. 111 222 333 444 555 666 777d. 1111 2222 3333 4444 5555 6666 7777
- A male Drosophila from a wild-type stock is discovered to haveonly seven chromosomes, whereas normally 2n = 8. Closeexamination reveals that one member of chromosome IV (thesmallest chromosome) is attached to (translocated to) the distalend of chromosome II and is missing its centromere, thusaccounting for the reduction in chromosome number. (a) Diagram all members of chromosomes II and IV duringsynapsis in meiosis I.In an electrophoretic gel across which is applied a powerful electrical alternating pulsed field, the DNA of thehaploid fungus Neurospora crassa (n = 7) moves slowlybut eventually forms seven bands, which represent DNAfractions that are of different sizes and hence havemoved at different speeds. These bands are presumed tobe the seven chromosomes. How would you show whichband corresponds to which chromosome?In Neurospora, his2 mutants require the amino acidhistidine for growth, and lys4 mutants require theamino acid lysine. The two genes are on the samearm of the same chromosome, in the ordercentromere - his2 - lys4.A his2 mutant is mated with a lys4 mutant. Draw all ofthe possible ordered asci that could result from meioses in which the following events occurred, accountingfor the nutritional requirements for each ascospore.Ascospores without any copy of a chromosome willabort and die, turning white in the process.a. A single crossover between the centromere and his2b. A single crossover between his2 and lys4c. Nondisjunction during the first meiotic divisiond. Nondisjunction during the second meiotic divisione. A single crossover between the centromere andhis2, followed by nondisjunction during the firstmeiotic divisionf. A single crossover between his2 and lys4,followed by nondisjunction during the firstmeiotic division
- In a vial of Drosophila, a research student noticedseveral female flies (but no male flies) with bag wingseach consisting of a large, liquid-filled blister insteadof the usual smooth wing blade. When bag-wingedfemales were crossed with wild-type males, 1/3 of theprogeny were bag-winged females, 1/3 were normalwinged females, and 1/3 were normal-winged males.Explain these results.The human genome consists of 23 pairs of chro-mosomes (22 pairs of autosomes and one pair of sex chro-mosomes). During meiosis, the maternal and paternal setsof homologs pair, and then are separated into gametes, sothat each contains 23 chromosomes. If you assume thatthe chromosomes in the paired homologs are randomlyassorted to daughter cells, how many potential combina-tions of paternal and maternal homologs can be gener-ated during meiosis? (For the purposes of this calculation,assume that no recombination occurs.)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)?
- We have discussed meiosis in yeast. One ascus e one melotic event. Two haploid yeast strains are crossed together, one wild type, the other mutant for 2 linked genes. The resulting diploid strain undergoes melosis eventually (=many meiotic events > many asci). A. What will the results be if the 2 genes are very far away from each other (certainly more than 50 map units)? B. What will the results be if the two genes are right next to each other, "no distance at all, zero distance"? (Explain your answers). Results here are patterns of asci and their percentages. Like for example "50% tetratypes, 0% ditypes", etc. If you forgot what a ditype or a tetratype is, you can illustrate them like that.Suppose that meiosis occurs in the transient diploid stageof the cycle of a haploid organism of chromosome number n. What is the probability that an individual haploidcell resulting from the meiotic division will have a complete parental set of centromeres (that is, a set all fromone parent or all from the other parent)?In a haploid yeast strain, eight recessive mutationswere found that resulted in a requirement for theamino acid lysine. All the mutations were found to revert at a frequency of about 1 × 10−6 except mutations5 and 6, which did not revert. Matings were madebetween a and α cells carrying these mutations. Theability of the resultant diploid strains to grow onminimal medium in the absence of lysine is shown inthe following chart (+ means growth and − means nogrowth.)1 2 3 4 5 6 7 81 − + + + + − + −2 + − + + + + + +3 + + − − − − − +4 + + − − − − − +5 + + − − − − − +6 − + − − − − − −7 + + − − − − − +8 − + + + + − + −a. How many complementation groups were revealedby these data? Which point mutations are foundwithin which complementation groups?The same diploid strains are now induced to undergosporulation. The vast majority of resultant spores areauxotrophic; that is, they cannot form colonies whenplated on minimal medium (without lysine). However,particular diploids can produce rare spores…