A prokaryotic endogenote of genotype his+ leu+ met+ trp+ ala+ undergoes with an
ID: 173057 • Letter: A
Question
A prokaryotic endogenote of genotype his+ leu+ met+ trp+ ala+ undergoes with an exogenote and now requires leucine supplementation to live. Which of the answers could explain this outcome? a.) The exogenote must have contained the allele 'leu-'. b.) An uneven number of crossovers took place. c.) An even number of cross-overs occurred. d.) The recombined genome of the endogenote turned it into an auxotrophic e.) All the answers are correct except for B. Of the following statements, four are 'fake news' and only one is correct. Which TRUE? a.) Recombination involves DNA strand breakage and invasion of the homologous chromosome; whether or not the sister chromatids exchange DNA with one and irrelevant since their genetic information will be identical. b.) By default, a human male's sperm will always carry a Y chromosome. c.) An organism with 44% thymine in its DNA will have 6% cytosine since C and T at single-ring structures. d.) By its very nature, an epistatic gene represents a lethal allele since it overrides the of another gene. e.) A mitochondrial disorder will appear in all of the offspring of an affected father. What is the middle gene in the following outcome from a 3-point test cross? a.) b is the middle gene b.) y is the middle gene c.) z is the middle gene d.) + is the middle gene e.) I wish I knew.Explanation / Answer
1)
Conjugation between endogenote and exogenote results leucine auxotrophic mutant. This can be explained by exogenote having allele leu- , the endogenote strain have turned into auxotrophic mutant and even numbered crosses between endogenote and exogenote might have resulted in the formation of leu- mutant. Therefore, option e is correct.
2) Recombination takes place by breakage of DNA strands and exchange of sister chromatids between homologous chromosomes. In DNA % of A= % of T and % of G = % of C. When T is 44%, A = 44%. Then, C and G are 6% each. This % of bases is according to base pairing but not due to their structures. Epistasis is masking of effect of phenotype of an allele by other alleles at the same locus. Mitochondrial disorders are inherited from mother but not from father. Human sperms contain X and Y chromosomes. Y chromosome occurs only in males. Therefore, option b is correct.
3)
Total number of gametes = 310 + 502 + 119 + 496 + 112 + 3 + 307 + 5 = 1854
Frequency of + = 310 + 502 + 119 + 496 + 112 + 3 + 5 = 1547 / 1854 = 0.83
Frequency of b = 119 + 496 + 307 + 5 = 927 / 1854 = 0.5
Frequency of y = 502 + 112 + 307 + 5 = 926 / 1854 = 0.499
Frequency of z = 502 + 119 + 3 + 307 = 931 / 1854 = 0.502
The b gene is in the middle. The order of genes is y , b, z. Therefore, option a is correct.
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