Recessive alleles are best defined as recessive alleles are best defined as a deleterious or disease-causing allele a weakened or attenuated allele an allele only expressed when the allele is homozygous the least frequently expressed allele in a given population

a deleterious or disease-causing allele  (may not always be the case, it may simply be expressing other phenotypic trait which is not harmful to the organism)

a weakened or attenuated allele (may not be the case, recessive alleles are not indicative of the strength of the allele)

an allele only expressed when the allele is homozygous (correct answer)

the least frequently expressed allele in a given population (not true, recessive alleles do not necessairily mean it is the least frequently expressed allele)

hey bro i looked it up on google the structure of the eye-spot in euglena viridie, e. ehrenbergii, and phacus pyriyorme is not as franzé haa described it. the so-called “crystal body” and “lens bodies” were not found in any of the individuals of the species examined by me. as earlier observers have stated, the eye-spot consists simply of a mass of pigment granules arranged in a single layer, and probably embedded in a protoplasmic framework, but the latter could not be seen, and its presence was only inferred from the fact that the pigment granules must be held together in some way, thd the eye-spot as a whole is capable of expansion, and that the pigment granules can be separated from each other.

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