Question

Another Example of Dominant and Recessive

Below is the pedigree of Sam's family that you saw in Lesson 3. Use what you have learned about dominant and recessive genes to explain how Sam has sickle cell disease when neither of his parents does.

In Lesson 3. you read about Sam, the boy with sickle-cell anemia. You learned that sickle-cell anemia is a disease that is inherited. But neither of Sam's parents had the disease. Sometimes the dominant gene. in this case the gene that produces non-sickle blood cells, is not completely dominant over the recessive gene. Both alleles give instructions for how cells are formed. If a person inherits both recessive alleles. then they inherit the disease, and their body makes only sickle cells. An individual must get the instructions to make sickle cells from both parents Ar individual that has one of each kind of allele has blood cells of both types sickle cell and normal. This kind of dominance is called co-dominance. The prefix co- means together, like in the word cooperate (work together). In the case of alleles that are co-dominant. they both produce phenotypes in the individual. but neither one are completely dominant.

Answer 1

Sam inherited both of his parents' recessive alleles leading to sickle-cell anemia.

Step-by-step explanation:

When looking at genes and their expression, there tend to be two main types; dominant, and recessive. Dominant genes/alleles will usually "take over" leading to a certain gene being expressed. Recessive alleles will normally "hide" if you will, and are often not expressed in favor of the dominant allele being expressed. However, there's an exception when two recessive alleles are present.

It results in the recessive allele being expressed. In this case, Sam's parents both carried a recessive allele for sickle-cell anemia, and they also both had a dominant allele that prevented sickle-cell anemia from being expressed (normal red-blood cells). When they had Sam, he inherited both of their recessive alleles, which led to him having sickle-cell anemia.