The use of genetics to infer evolutionary relationships among groups of organisms depends on the basic assumption that an organism inherits its genes from its parents. This is known as vertical gene transfer (VGT). Biologists now realize that organisms are also able to acquire genes in a different way, known as horizontal gene transfer (HGT). During HGT, an organism acquires new genes from another organism in its environment, genes which it can then pass on to its descendants. In some cases, an organism acquires genes from a donor that it is only distantly related to. This has the potential to act as a confounding factor when biologists use horizontally acquired genes to infer relationships among groups of organisms.
Recognizing this potential problem, Carl Woese pioneered the use of genes encoding ribosomal RNA (rRNA) to construct the relationships among groups of organisms. These genes are passed vertically from parent to offspring, with little or no horizontal gene transfer. An additional benefit of using genes which encode rRNA is that they are present in all forms of life, from single-cellular bacteria to multi-cellular plants and animals.
According to the passage, which of the following is an advantage of using genes that encode rRNA to infer the evolutionary relationship among groups of organisms?
a. They are broadly distributed across all forms of life.
b. They are seldom transferred between distantly related organisms.
c. They are inherited from an organism’s direct ancestors.
The correct answer is a,b, and c.
I understand why a and b are correct, but what wording here proves that option c also is correct? Based on the passage “These genes are passed vertically from parent to offspring, with little or no horizontal gene transfer.” The highlighted part shows that some gene transfer can happen without parents. So what wording in option c “They are inherited from an organism’s direct ancestors.” allow us to neglect the fact that some gene transfer can be transferred and not inherited from ancestors?