BIOL 1020 Lecture 27: Lecture 27
BIOL 1020 Full Course Notes
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Below are data from a three-point linkage experiment in Drosophila melanogaster. These data represent the offspring from a testcross between flies expressing the recessive mutant phenotypes for black body, vestigial wings and brown eyes and flies that express normal wild type phenotypes but are heterozygous for all three traits. All the heterozygous wild type parental flies in this cross start out with mutant alleles in the cis configuration. Answer the following questions based on these data and show your work for question 1 (a-d).
| Body | Wing | Eye | Phenotype | Count |
| b+ | vg+ | bw+ | Gray body, normal wings, red eyes | 103 |
| b | vg | bw | Black body, vestigial wings, brown eyes | 95 |
| b+ | vg | bw | Gray body, vestigial wings, brown eyes | 32 |
| b | vg+ | bw+ | Black body, normal wings, red eyes | 29 |
| b+ | vg+ | bw | Gray body, normal wings, brown eyes | 71 |
| b | vg | bw+ | Black body, vestigial wings, red eyes | 68 |
| b+ | vg | bw+ | Gray body, vestigial wings, red eyes | 10 |
| b | vg+ | bw | Black body, normal wings, brown eyes | 13 |
1a)Which combinations of phenotypes are only possible in those offspring derived from gametes resulting from double crossover events?
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1b)What is the distance between the body color (gray vs. black) and wing loci (normal vs. vestigial)?
1c)What is the distance between the body color (gray vs. black) and eye color loci (red vs. brown eyes)?
1d)What is the coefficient of coincidence for double crossovers?
Please show detailed work. Thanks in advance.
16. Syntenic genes can assort independently when
A) they are very close together on a chromosome.
B) they are located on different chromosomes.
C) crossing over occurs rarely between the genes.
D) they are far apart on a chromosome and crossing over occurs frequently between the genes.
E) they are far apart on a chromosome and crossing over occurs very rarely between the genes.
17. The alleles of linked genes tend to
A) segregate together more often than expected by random assortment
B) assort independently.
C) be mutated more often than unlinked genes.
D) experience a higher rate of crossing over.
E) assort independently and show a higher rate of crossing over.
18. If you know that the frequency of recombination between genes X and Y is 34% and between X and Z is 25%, can you predict the order of the three genes?
A) Yes; the order is X-Z-Y.
B) Yes; the order is X-Y-Z.
C) Yes; the order is Z-X-Y.
D) No; based on this data alone, the order could be Z-Y-X or X-Y-Z.
E) No; based on this data alone, the order could be X-Z-Y or Z-X-Y.
Question 19 - 20. You have performed the following dihybrid cross in Drosophila using the black body color (b) and vestigial wing (vg) mutations. The b+ (grey body) and vg+ (normal wing) are dominant wild type alleles. These genes are autosomal.
Female â b+ vg+/b vg à male â b vg/b vg
Progeny:
Phenotype # of Progeny
Grey body normal wing 965
Black body vestigial wing 944
Grey body vestigial wing 208
Black body normal wing 195
19. Assuming linkage between black and vestigial, the estimated recombination frequency would be:
0.17
0.09
0.82
1.00
0.50
20. What key test could you use to determine whether the observed offspring frequencies deviate from those expected by chance alone?
A) Pascal's triangle
B) The product rule
C) The Chi-square (Ï2) test
D) The law of random assortment
E) The sum rule
21. In a genome wide association study (GWAS) designed to map the gene(s) that control height you divide subjects into a group of 1000 who are all more than seven feet tall and a control group of 1000 people of average height. You find the following associations between two genetic markers and the height trait:
| Tall group | Control group | ||
| Marker 1 | Allele A | 20% | 50% |
| Allele T | 80% | 50% | |
| Marker 2 | Allele G | 15% | 15% |
| Allele C | 85% | 85% |
What is your best guess for which marker is more closely linked to a gene that influences height?
A) Marker 1
B) Marker 2
22. Two pure breeding parents produce red and white flowers. They are crossed and the F1 produces pink flowers. When the F1 are selfed to produce the F2, nine distinct classes of pigmentation are present among F2 individuals. What is your best guess of the minimum number of genes that underlie flower pigmentation in this species?
A. 2
B. 3
C. 4
D. 5
E. 6
23. In a quantitative genetic experiment you identify two genes that confer bands of color on the back of a fly. At each gene, a dominant allele causes one band of color. If flies that are heterozygous at both loci are crossed, what ratio of offspring do you expect in each phenotype (i.e., number of color bands) class? (answer options are given from lowest to highest band number)
A) 1:1:1:1:1
B) 1:2:2:2:1
C) 1:4:6:4:1
D) 4:4:4:4:4
