The sickle-cell allele is pleiotropic (that is, it affects more than one phenotypic trait). Specifically, this allele affects ox
ygen delivery to tissues and affects one's susceptibility to malaria. Heterozygous individuals who have one normal and one sickle-cell allele have a phenotype that has both costs and benefits. The cost: Under conditions of low atmospheric oxygen availability, individuals heterozygous for this allele can experience life-threatening sickle-cell "crises." The benefit: Such individuals are less susceptible to malaria. Thus, pleiotropic genes/alleles reveal that ________.
The pleiotropic gene involved in sickle-cell anemia is an example of heterozygous advantage. This means that the heterozygous genotype is favourale over other two genotypes (recessive homozygous and dominant homozygous). Eventhough it has harmful effect (sickle cell disease carrier) heterozygous genotype enables resistance to infection (malaria) and that is why this genotype is still favourable by natural selection. This phenomenon is evidence of compromise between harmful ad benefit.
Answer: The speaker admires and appreciates the librarian. She remembers the librarian's friendliness and how much effort she would make to provide the speaker with the books she wanted. These books were very meaningful and important to the speaker.
Explanation: Because i did the question on edgenuity
