Answer:
b. form of a gene
Explanation:
An allele is a variant form of a gene. Some genes have a variety of different forms, which are located at the same position, or genetic locus, on a chromosome. Genotypes are described as homozygous if there are two identical alleles at a particular locus and as heterozygous if the two alleles differ.
<span>A retrovirus is anything of a group of RNA viruses that insert a DNA copy of their genome into the host cell to replicate.
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<span>A tropism is a movement of an organism toward or away from a stimulus. A positive tropism is when the organism moves toward the stimuli. A negative tropism is when the organism moves away from the stimuli. So, your answer will be negative tropism, since the stem is growing up and out of the soil, AWAY from gravity.</span>