Exam 7: Linkage and Chromosome Mapping in Eukaryotes

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 is the relationship between the degree of crossing over and the distance between two genes?

Positive interference occurs when a crossover in one region of a chromosome reduces crossovers in nearby regions.

Methods for determining the linkage group and genetic map in humans involve _.

Three loci, mitochondrial malate dehydrogenase that forms a and b (MDHa, MDHb), glucouronidase 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.

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

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 _.

Assume that a cross is made between AaBb and aabb plants and that the offspring occur in the following numbers: 106 AaBb, 48 Aabb, 52 aaBb, 94 aabb. These results are consistent with which arrangement of alleles?

Diagram chromosomal events that will ultimately result in the segregation of alleles (A and a) during meiosis II rather than meiosis I.

(a) In a three -point mapping experiment, which three general classes of offspring are expected (assuming crossovers occur)? (b) How many different genotypic classes are expected?

Assume that the genes for tan body and bare wings are 15 map units apart on chromosome II in Drosophila. Assume also that a tan -bodied, bare -winged female was mated to a wild -type male and that the resulting F1 phenotypically wild -type females were mated to tan -bodied, bare -winged males. Of 1000 offspring, what would be the expected phenotypes, and in what numbers would they be expected?

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

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

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

Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second chromosome with a strain homozygous for the second chromosome recessive mutations smooth abdomen and straw body. The F1 Lobe females were then backcrossed with homozygous smooth abdomen, straw -body males, and the following phenotypes were observed: a() Give the gene order and map units for these three loci. b() What is the coefficient of coincidence?

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.

The coefficient of coincidence reflects the frequency of observed double crossovers compared to the frequency of expected double crossovers. What is the relationship between the coefficient of coincidence and interference?

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 G and E loci assort independently.