Exam 5: Chromosome Mapping in Eukaryotes

What two terms apply to the fusion of cultured human and mouse cells that produces cell lines that are useful in assigning a gene to a particular human chromosome?

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.

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 what arrangement of genes?

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

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?

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.

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

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 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:

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

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

Methods for determining the linkage group and genetic map in humans involve which of the following?

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 the following circumstance:

Describe a convenient method for determining gene order from three-point cross results.

Phenotypically wild-type F₁ female Drosophila, whose mothers had light eyes (lt) and fathers had straw (stw) bristles, produced the following offspring when crossed to homozygous light-straw males:

Phenotype	Number
light-straw	22
wild-type	18
light	990
straw	970
total	2000

Compute the map distance between the light and straw loci.

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

Given that loci A and B in Drosophila are sex-linked and 20 map units apart, what phenotypic frequencies would you expect in male and female offspring resulting from the following crosses? (Assume that A and B are dominant to a and b, respectively.) a) AaBb (dominant alleles on same chromosome) female × ab/Y male b) AaBb (dominant alleles on homologs) female × ab/Y male c) aabb female × AB/Y male (no crossing over in male 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.

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

Sister chromatid exchanges increase in frequency in the presence of X-rays, certain viruses, ultraviolet light, and certain chemical mutagens. In what autosomal recessive disorder is there known to be an increase in sister chromatid exchanges?