question...can you please also explain the correct answers Human cells completel

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question...can you please also explain the correct answers

Human cells completely lack the ability to use ______ to repair DNA damage caused by excessive exposure to sunlight. a. Nucleotide excision repair b. Base excision repair c. Direct repair d. Mismatch repair We have often discussed the concept of necessity vs. sufficiency as it applies to genetic analysis. Which of the following would demonstrate that the fruitless (fru) gene is necessary for male mating behavior in flies? a. mutation of the mouse fru homolog results in changes in mating behavior in mice b. ectopic expression of fru in female flies causes them to exhibit male mating behavior c. fru was cloned and shown to encode a transcription factor d. loss-of-function mutations in the fru gene cause abnormal or absent male mating behavior

Explanation / Answer

3. Human cells completely lack the ability to use c. Direct repair to repair DNA damage caused by excessive exposure to sunlight.

Explanation : Excessive exposure to sunlight may cause mutation by UV radiation. This produce thymine dimer in which adjacent thymine on the same strand of DNA are joined by the formation of a cyclobutane ring resulting from saturation of the double bonds between carbons 5 and 6. This blocks replication and transcription. To repair this a direct process called photoreactivation takes place. Photoreactivation breaks the cyclobutane ring structure. This process is absent in human.

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