Exam 5: Genetic Linkage and Mapping in Eukaryotes

In fruit flies, red eyes (pr+_) are dominant to purple eyes (prpr) and normal wings (vg+_) are dominant to vestigial wings (vgvg). The genes are located on the same chromosome. A pure breeding red- eyed fly with vestigial wings was crossed with a pure- breeding purple- eyed fly with normal wings. All of the F1 progeny had a WT phenotype. Which of the following represents the arrangement of alleles on the F1's chromosome?

You perform a test cross of the dihybrid AaBb and score the phenotypes of 1000 progeny. Assuming independent assortment, how many of the progeny do you expect to display the dominant phenotype for both the A and B genes?

If you are given a recombination frequency of 34% between genes X and Y and 27% between X and Z, can you predict the order of the three genes?

Incomplete genetic linkage of three genes in a trihybrid produces eight genetically different gamete genotypes. How many different gamete genotypes are produced in a four- gene cross with incomplete genetic linkage?

For a given haplotype, the frequencies of alleles for gene Y are Y = 0.55 and Y' = 0.45, and the frequencies at gene Z are Z = 0.15 and Z' = 0.85. What is the predicted frequency of the YZ haplotype in a population in linkage equilibrium?

William Bateson and Reginald Punnett were not able to detect genetic linkage in sweet peas. Which of the following explains why Thomas Morgan was able to detect autosomal genetic linkage?

The order of genes on a plant chromosome is A, B, and D, where A and B have a recombination frequency of 0.2, and B and D have a recombination frequency of 0.3. A pure- breeding plant that has the dominant A and D phenotypes with a recessive b phenotype is crossed to a pure- breeding plant that has the recessive a and d phenotypes with the dominant B phenotype. The resulting hybrid is crossed to a plant that has all three recessive phenotypes. Under the assumption that the value for interference in this region is zero, what percentage of each progeny type would result from a single crossover between B and D?

Genes A and B are 7.5 map units apart on one chromosome. Genes C and D are 8.0 map units apart on a second non- homologous chromosome. The recombination frequency between A and C is ________.

When constructing a genetic map of Zea mays, Creighton and McClintock used genetic markers as well as structural differences in the homologous copies of chromosome 9 that can be seen under the microscope. What are these structural differences called?

For a given cross, the expected number of double recombinants is 18 and the observed number of double recombinants is 12. What is the interference (I)?

A geneticist is mapping the chromosomes of a new fish species. These fish have genes for the dominant traits non- bioluminescent (B), ventral eyes (D), and short spikes (L) with corresponding recessive traits bioluminescent (b), dorsal eyes (d), and long spikes (l). He test- crosses one of these fish who is dominant at all th loci to determine if the three genes are linked resulting in the data shown below: $\frac{(345-125)^{2}}{125}+\frac{(355-215)^{2}}{125}+\frac{(42-125)^{2}}{125}+\frac{(38-125)^{2}}{125}+\frac{(105-125)^{2}}{125}$ $+\frac{(95-125)^{2}}{125}+\frac{(9-125)^{2}}{125}+\frac{(11-125)^{2}}{125}=1148$ a) Why are these data consistent with genetic linkage among the three genes? b) Perform a chi- square test to determine if these data show significant deviation from the expected phenotype distribution. c) Determine the recombination frequencies between each pair of genes. d) Determine the coefficient of coincidence (COC) and interference (I) values for this data set.

A geneticist is mapping the chromosomes of the newly captured gremlin. Stripe is heterozygous for linked genes with alleles Bb, Ee, and Hh that determine if gremlins have biting teeth (B), are evil (E), have hair (H). In order to determine if the three genes are linked, a standard testcross was done, and 1000 offspring had the following genotypes: 48 bb ee 36 Bb ee hh 400 Bb ee 4 Bb Ee Hh 426 bb Ee hh 46 Bb Ee hh 38 bb Ee Hh 2 bb ee hh What is the recombination frequency between genes E and B?

Instead of creating a gene map along a chromosome,________ is a method of analysis that detects and locates the genes that, as a group, influence form or appearance.

In sweet peas, the genes for flower color and pollen grain shape are 11 cM apart. A pure- breeding purple flowering plant with round pollen grains is crossed to a pure- breeding red flowering plant with long pollen grains. The resulting F1 offspring are all purple flowering plants with long pollen grains. What percent of offspring from a test cross analysis of the F1 individuals would you expect to be purple flowering plants with long pollen grains?

How is Newton Morton's statistical method (Lod score analysis) helpful for calculating the overall probability of genetic linkage when allelic phase is unknown?

Syntenic genes can assort independently when________ .

Compare and contrast the following three DNA genetic markers: variable number tandem repeats (VNTRs), single nucleotide polymorphisms (SNPs), and restriction fragment length polymorphisms (RFLPs).

The pedigrees below are for a dominant disease where individuals with the dominant disease allele (D) are affec Individuals that were alive were also screened for a polymorphic DNA marker that has six alleles identified as P P4, P5, and P6. a) In Family B, explain why the P1 marker cannot be assumed to be transmitted with the dominant allele given there is no haplotype data for the first generation. b) In Family A, how does the information regarding the haplotype of individuals in the first generation allow y determine the allelic phase of the disease? "Use Figure 5.15 in Chapter 5, page 169 from main title."

In most tests of genetic linkage, the number of double crossovers is LESS than the number expected due to what effect, which limits the number of crossovers that can occur in a short length of chromosome?

If there is a maximum Lod score of 4.2 at 0 = 0.31, what can you say about the linkage and the distance between two genes?