Some bacteria have an R plasmid. These can be transferred from one bacterium to another through horizontal gene transfer. Why are these R plasmids so important?

Explanation:

Circular piece of DNA that exists outside (in the cytoplasm) of the main bacterial chromosome  are known as R plasmid, they replicate independently of chromosomal DNA.

R plasmid play very important role in horizontal gene transfer , they contain genes which are necessary for gene transfer.

R plasmid transfer from donor to recipient cell.

Let attached earlobes allele be represented by a and free earlobe allele be represented by A.

Parent genotypes are Aa (heterozygous for free earlobes) and aa (homozygous recessive for attached earlobes, recessive traits occur in recessive pairs). Possible offspring genotypes are thus Aa and aa, given that the child inherits one allele from each parent. The probability of either genotype for the offspring is 50/50 hence the probability of the child having attached earlobes (aa) is 0.50.