BIO 325 - Fall 2009 - Sample questions - Exam 2 - Key

BIO 325 - Fall 2009 - Sample questions - Exam 2 - Key -...

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GENETICS (BIO 325) Fall 2009 Key - Sample questions – Exam 2 __________________________________________________________________________________ 1. (a) 1: 1: 2 A/a; B/b : A/a; b/b : a/a; B/b and a/a; b/b (b) 1: 3 A/a; B/b : A/a; b/b, a/a; B/b, and a/a; b/b (c) 2: 1: 1 A/a; B/b and A/a; b/b : a/a; B/b : a/a; b/b (d) 3: 1 A/a; B/b, A/a; b/b, and a/a; b/b : a/a; B/b (e) 3:1 A/a; B/b, A/a; b/b, and a/a; B/b : a/a; b/b 2. Individual A carries the dominant allele. The trait exhibits incomplete penetrance. 3. (a) Recessive epistasis (b) 12 gray, 3 black, 1 brown 4. (a) (b) (c) 5. 6. In the cross, Hfr (pro + ) x F - (pro - ), the F plasmid is excised imprecisely from the Hfr chromosome in the first step. The excised F carries pro + gene of the donor chromosome, resulting in F’pro + . This F’ carrying the pro + gene is next transferred to the F - (pro - ) cells early in the mating process. Cells carrying an F’pro + , when used in further matings, convert a majority of the F - (pro - ) cells to F’pro + cells. 7. Genes a and b are very close to each other on the chromosome and gene c is at a distance from these two genes. 8. (a) Gene for resistance to drug B is the distant gene. try arg thy mal thi thr azi bio 2 met 4 his phe
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(b) adc or cda 9. (i) The lysogenic transductants (ii) These transductants are formed by recombination between the gal + carrying λ dgal + and the gal - gene on the recipient chromosome. 10. 11. Grow P1 on wild-type E. coli cells containing the pro + gene. P1 cleaves up the bacterial DNA into small fragments and packages them into P1 phage particles. A small number of phages will package the pro + gene. When this particle injects its DNA into a pro - strain of E. coli , the cells which survive in the absence of proline will be those resulting from homologous recombination between the phage pro + allele and the chromosomal pro - allele. 12. The gene order is trp-ala-pro . 13. (a) The attachment site, att , must be between genes f and g . (b) badc or cdab 14. (a) a + b - c - str s d - and a + b + c - str s d - (b) No. Once the prophage enters the recipient, zygotic induction takes place and exconjugants for markers that appear after the λ insertion site will be recovered. Since the Str r marker follows the λ during transfer, no streptomycin resistant exconjugants will be obtained. 15. Avery, MacLeod and McCarty identified the nature of the transforming principle present in the heat-killed S strain of Streptococcus pneumoniae that was able to transform cells of the live R strain into the S strain. They destroyed specific types of molecules in the heat-killed S strain using either enzymes or other methods and incubated them with the live R strain. When DNA was destroyed in the heat-killed S strain extract and this was incubated with the live R strain, no live S strain cells were recovered. In other words, destruction of DNA did not result in the 2
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transformation. Therefore, these experiments demonstrated that DNA is the transforming principle and provided evidence that the genetic material is DNA. 16.
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This note was uploaded on 01/19/2010 for the course BIO Genetics taught by Professor Saxena during the Fall '08 term at University of Texas.

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BIO 325 - Fall 2009 - Sample questions - Exam 2 - Key -...

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