Exam 7: Linkage, Recombination, and Eukaryotic Gene Mapping

A) linkage over DNA
B) linkage of dihybrids
C) long overall distances (with respect to map distances)
D) linker of DNA
E) logarithm of odds

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A) assort randomly.
B) cannot cross over and recombine.
C) are allelic.
D) co-segregate.
E) will segregate independently.

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A) Lod-score analysis relies on family or pedigree data, while association studies use population data.
B) Lod-score analysis requires that the loci being mapped must be on different chromosome arms, while association studies can map genes on different chromosomes.
C) Association studies compare genotypes between parents and their children, while lod-score analysis compares genotypes between siblings of the same family.
D) Lod-score analysis requires isolated human populations, while association studies require very large family pedigrees.
E) Lod-score analysis requires a large number of genes with multiple alleles, while association studies can use genes that have only two alleles.

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A) The B locus is on the X chromosome, so it can never produce a white phenotype.
B) The B allele is actually codominant with the b allele, so a white phenotype cannot be produced.
C) The recessive l allele is in tight coupling linkage with the b allele, so almost all of the bb offspring will also be ll and thus die before they can be observed.
D) The dominant L allele is in tight repulsion linkage with the B allele, so it will be impossible to produce the Bb genotype that would express the white phenotype.
E) Normally, it would be expected that 25% of the offspring would be white, but in this case, random deviations from the expected resulted in no white offspring.

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To map the new gene with respect to the ...

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A) 53 m.u.
B) 5.3 m.u.
C) 0.53 m.u.
D) 10.6 m.u.
E) 25 m.u.

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A) positions in the genome where people vary by a single nucleotide base
B) the probability that two genes are linked
C) the nonrandom association between alleles in a haplotype
D) the occurrence of two alleles in the repulsion configuration
E) crossing over that occurs between two genes that are located close to each other

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A) Genetic recombination of alleles is associated with physical exchange between chromosomes.
B) Genes are located on chromosomes and the map distance between them could often be measured by the number of nucleotides in the DNA.
C) Determining map distances in humans could be done by using pedigrees and calculating lod scores.
D) Association studies allow genes that have no obvious phenotype to be accurately mapped.
E) Crossing over does not occur in male Drosophila, so there is no genetic recombination.

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A) 45 m.u.
B) 22.5 m.u.
C) 10 m.u.
D) 5 m.u.
E) 2.5 m.u.

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A) cannot exceed 100 m.u.
B) are dependent on crossover frequencies between paired, nonsister chromatids.
C) can be measured in centiMorgans or map units.
D) cannot be determined.
E) can only be determined by physical mapping techniques.

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A) one parent who is homozygous recessive for one gene pair and a second parent who is homozygous recessive for a second gene pair.
B) one parent who is homozygous dominant for one or more genes and a second parent who is homozygous recessive for these same genes.
C) two parents who are both heterozygous for two or more genes.
D) one parent who shows the dominant phenotype for one or more genes and a second parent who is homozygous recessive for these genes.
E) one parent who shows the recessive phenotype for one or more genes and a second parent who is homozygous dominant for these genes.

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A) 1 m.u.
B) 5 m.u.
C) 10 m.u.
D) 20 m.u.
E) 30 m.u.

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A) 12 m.u.
B) 50 m.u.
C) 16 m.u.
D) 5 m.u.
E) 25 m.u.

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A) Somatic-cell hybridization experiments are not very accurate, and the gene may be on chromosome 5 or chromosome 7 instead of chromosome 6.
B) Too few recombinants could be found to indicate linkage in the lod-score analysis.
C) A lod-score analysis cannot be used when a DNA marker locus needs to mapped with respect to a gene locus.
D) The gene and the DNA marker locus are so far apart on chromosome 6 that they assort independently.
E) There were probably too few double-crossover events occurring between the two loci, so the lod score could not be determined accurately.

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A) the distance in numbers of nucleotides between two genes
B) the number of genes on each of the chromosomes of a species
C) the linear order of genes on a chromosome
D) the location of chromosomes in the nucleus when they line up at metaphase during mitosis
E) the location of double crossovers that occur between two genes

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A) far fewer double-crossover recombinant progeny were recovered from a testcross than would be expected from the map distances of the genes involved.
B) crossing over has been enhanced for genes that are located near the centromere of chromosomes because there is less interference of one crossover on the occurrence of a second crossover event.
C) single-crossover recombinant classes in the progeny have been increased because the genes involved produce lethal phenotypes when in parental gene combinations.
D) there is a large map distance between one of the outside genes in the heterozygous parent and the middle gene, while there is a short map distance between the middle gene and the other outside gene.
E) the physical distance between two genes is very short compared with the genetic map distance between these two genes.

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A) phenotypes that are similar.
B) recombination frequencies of less than 50%.
C) homozygosity when involved in a testcross.
D) a greater number of recombinant offspring than parental offspring when involved in a testcross.
E) a lack of recombinant offspring when a heterozygous parent is involved in a testcross.

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A) about 14
B) about 26
C) about 10
D) about 4
E) none because of crossover interference

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