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Spike 11041 11141 Ala Asn SARS COV 2 GTC CTA TAT AAT TCC GCA TCA TTT TCC ACT Bat RaTG13 GTC CTA TAT AAT TCC ACT TCA TTT TCT ACC PCOV GX P5L GTA CTT TAT AAC TCT ACA TCA TTT TCC ACT Bat SARS Rs4231 GTA CTC TAC AAC TCA ACA TCT TTT TCA ACT GTA CTC TAC AAC TCA ACA TCT TTT TCA ACT Thr Bat BtRs A study published in Cell in 2021 presented a comparative analysis of the genomic sequences of thousands of SARS CoV 2 viruses isolated from humans i e strains causing COVID bats and pangolins This study asked what sequence changes occurred when this virus moved from bats to humans that might help explain its success as a human pathogen The sequence diagram shown above presents a key finding of the study an A in the spike protein gene coding region found in bat and pangolin viruses changed to a G in human SARS CoV 2 isolates only shown here once but found in all viruses from human COVID patients that were sequenced This mutation changes a Thr codon to an Ala codon In vitro spike protein with an Ala at this position binds more tightly to the ACE2 virus receptor on human cells and infects cultured human lung cells more efficiently than proteins with Thr at this position Part 1 O Which of the following Hardy Weinberg violations that can change allele frequencies over time is the most likely explanation for these findings 11241 Genetic drift the G allele arose and became fixed as SARS CoV2 moved from bats to humans due to random fluctuation in allele frequencies in a small population of viruses Genetic drift the A allele was lost as SARS CoV 2 moved from bats to humans due to random fluctuation in allele frequencies in a small population of viruses O A selective sweep strong positive selection caused fixation of the G allele in the transition of SARS CoV 2 from bats to humans O Negative selection against the A allele caused it to be lost in the population of human SARS CoV 2 viruses Part 2 What rationale can you propose for your choice in Part 1 Note you will receive credit for any answer entered B I UT IEE F T

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