Exam 17: Large-Scale Chromosomal Changes

Assume you are studying an organism in which duplications or deficiencies in the gametes are not viable.An individual is heterozygous for a pericentric inversion.A four-chromatids double crossover,with both crossovers occurring within the inversion,would lead to:

In a haploid fungus,genes a and b are located on chromosome 2 and 7,respectively.A cross is performed between a strain that is genotypically a;b and has normal chromosomes,and a strain that is genotypically wild type but has a reciprocal translocation between chromosomes 2 and 7.If crossing over never occurs in this fungus,what is the expected proportion of tetrads resulting from the cross? Tetrad I Tetrad 2 Tetrad 3 Tetrad 4 Tetrad 5 Spore 1 aborted a;b A;B A;B A;B Spore 2 aborted a;b A;B A;B aborted Spore 3 aborted aborted abarted a;b a;b Spore 4 aborted aborted aborted a;b aborted

The n + 1 female gametophytes (embryo sacs)produced by trisomic plants are usually more viable than the n + 1 male gametophytes (pollen grains).If 50% of the functional embryo sacs of a selfed trisomic plant are n + 1 but only 10% of the functional pollen grains are n + 1,what percentage of the offspring will be diploid?

Assume you are studying an organism in which duplications or deficiencies in the gametes are not viable.An individual is heterozygous for a paracentric inversion.A four-chromatids double crossover,with one of the two crossovers within the inversion and the other outside of it,would lead to:

In an animal bearing the heterozygous inversion ABCDE[*]FGHI / ABGF[*]EDCHI,in one meiocyte,a crossover occurred between the D and E loci and another crossover occurred between the F and G loci.The two crossovers involved the same two chromatids.What will be the proportion of abnormal meiotic products from that meiosis? (Note: [*] = centromere.)

A plant trisomic for a chromosome carrying the A gene has the genotype A/a/a.Which of the following represents a gamete this plant could NOT produce?

In Zinnia plants (n = 16),the chromosomes of autotetraploids pair in twos.The locus for flower color (R = red,r = white)is close to the centromere on chromosome 5,and the locus for plant height (D = tall,d = dwarf)is also closely linked to the centromere on chromosome 11.Both dominant alleles show full dominance over any number of recessive alleles. a)If you are observing meiosis in tetraploid Zinnias,what is the total number of bivalents (chromosome pairs)that will be visible during prophase I? Explain. b)In a pollen cell from a tetraploid plant,how many chromosomes will be present? c)If a tetraploid plant of genotype R/R/r/r;D/D/D/D is selfed,what proportion of progeny will be white flowered and tall? d)If a tetraploid plant of genotype R/r/r/r;D/D/D/D is selfed,what proportion of progeny will be white flowered and tall? e)If a tetraploid plant of genotype R/R/r/r;D/D/d/d is selfed,what proportion of progeny will be white flowered and dwarf? What proportion will be red flowered and tall?

A meiocyte of an organism heterozygous for a reciprocal translocation goes through meiosis and results in four viable meiotic products.The most likely explanation is that:

A pure-breeding flowering plant with a long stem and small leaves was crossed to a pure-breeding individual of the same species that has a short stem and large leaves.The F₁ is comprised entirely of individuals with long stems and large leaves.When these F₁ individuals are testcrossed,they only produced about half as many individuals as expected.The phenotypic ratios were: 462 short stems and large leaves,450 long stems and small leaves,52 long stems and large leaves,and 50 short stems and small leaves. These 1022 plants were further crossed to a tester,and many of them displayed semi-sterility,in particular: of the 462 plants with short stems and large leaves,362 were semisterile. of the 450 plants with long stems and small leaves,90 were semisterile. of the 52 plants with long stems and large leaves,40 were semisterile. of the 50 plants with short stems and small leaves,10 were semisterile. Provide a plausible,comprehensive genetic explanation for these results.

In the diagram below,each of the five lines indicates the extent of a Drosophila deletion.A through G represent adjacent chromosomal regions (for example,in line 3 regions D and E are deleted). When a radioactive DNA fragment corresponding to a Drosophila gene of interest was incubated with chromosomes carrying each of the five deletions,it bound only to chromosomes carrying deletion 1 or deletion 5.Based on this information,the gene of interest is located in region: