Exam 5: Chromosome Mapping in Eukaryotes

Based on the classic experiments of Creighton and McClintock with maize,crossing over involves a physical exchange between chromatids.What particular chromosomal characteristic allowed their experiments to succeed?

Who was the student in Morgan's laboratory who first realized that the sequence of genes could be determined by Morgan's proposal that two genes located relatively close to each other are less likely to form chiasma between them than if the two genes were relatively far apart?

What relatively recent scientific advancement has made mapping by linkage or classical genetic mapping approaches virtually obsolete?

The phenomenon in which one crossover decreases the likelihood of crossovers in nearby regions is called

At what stage of the meiotic cell cycle and during what chromosomal configuration does crossing over occur?

Three loci,mitochondrial malate dehydrogenase that forms a and b (MDHa,MDHb),glucuronidase that forms 1 and 2 (GUS1,GUS2),and a histone gene that forms + and - (H⁺,ᴴ-),are located on chromosome #7 in humans.Assume that the MDH locus is at position 35,GUS at position 45,and H at position 75.A female whose mother was homozygous for MDHa,GUS2,and H⁺ and whose father was homozygous for MDHb,GUS1,and H- produces a sample of 1000 egg cells.Give the genotypes and expected numbers of the various types of cells she would produce.Assume no chromosomal interference.

Assume that a cross is made between AaBb and aabb plants and that the offspring fall into approximately equal numbers of the following groups: AaBb,Aabb,aaBb,aabb.These results are consistent with the following circumstance:

The cross GE/ge × ge/ge produces the following progeny: GE/ge 404; ge/ge 396; gE/ge 97; Ge/ge 103.From these data one can conclude that there are 20 map units between the G and E loci.

Assume that there are 12 map units between two loci in the mouse and that you are able to microscopically observe meiotic chromosomes in this organism.If you examined 200 primary oocytes,in how many would you expect to see a chiasma between the two loci mentioned above?

Two lines of work indicated that crossing over actually involves breakage and reunion of chromatid material.What organisms were involved,and who did the work?

Restriction fragment length polymorphisms (RFLPs),microsatellites,and single-nucleotide polymorphisms (SNPs)were used by Morgan and Sturtevant to discover linkage in Drosophila.

The cross GE/ge × ge/ge produces the following progeny: GE/ge 404; ge/ge 396; gE/ge 97; Ge/ge 103.From these data one can conclude that the recombinant progeny are gE/ge and Ge/ge.

What advantage does BrdU (bromodeoxyuridine)have in the study of chromosome structure and recombination?

In Drosophila,assume that the gene for scute bristles (s)is located at map position 0.0 and that the gene for ruby eyes (r)is at position 15.0.Both genes are located on the X chromosome and are recessive to their wild-type alleles.A cross is made between scute-bristled females and ruby-eyed males.Phenotypically wild-type F₁ females were then mated to homozygous double mutant males,and 1000 offspring were produced.Give the phenotypes and frequencies expected.

Under what circumstance might two loci be on the same chromosome but behave as if independently assorting in crosses?

If two gene loci are on nonhomologous chromosomes,genes at these loci are expected to assort independently.

If interference is complete,what would be the frequency of double crossovers?

The genes for mahogany eyes and ebony body are approximately 25 map units apart on chromosome III in Drosophila.Assume that a mahogany-eyed female was mated to an ebony-bodied male and that the resulting F1 phenotypically wild-type females were mated to mahogany,ebony males.Of 1000 offspring,what would be the expected phenotypes,and in what numbers would they be expected?

Exchanges occur between homologous chromosomes,but never between sister chromatids.

Assume that a cross is made between AaBb and aabb plants and that all the offspring are either AaBb or aabb.These results are consistent with the following circumstance: