Day 4, April 11

Hello! Today we began making our presentation video and continued answering more of the questions in the case study.

Now we will discuss autosomal recessive traits:

1. What are the hallmarks of an autosomal recessive trait?
   Autosomal recessive traits are characterized by males and females being having equal chances of becoming affected, the recurrence risk to the unborn sibling of an affected is individual is ¼, the trait is characteristically found in siblings not parents of affected or the offspring of the affected. Also, the parents of the children may be related depending on the rarity of the trait in the population.
2. What does consanguineous mean? Why is this concept especially important when discussing recessive genetic disorders?
   Consanguineous refers to people being of the same blood and descended from the same ancestors. This is important when discussing recessive genetic disorders because they are transmitted or inherited genetically through a person’s ancestors. The parent may therefore be related and consanguineous mating may be taking place.
3. What is it about the inheritance pattern of factor VIII deficiency seen in Greg and Olga’s pedigree that point toward it not being an autosomal recessive trait?
   Autosomal recessive traits affect both males and females equally. Factor VIII deficiency, on the contrary, only affect male, while women may be carriers of the disease. As shown in the pedigree, no females are affected.

Now that autosomal recessive traits have been discussed we proceed to the concept of X-linked recessive inheritance:

1. What are the the characteristics of X-linked recessive inheritance?
   X-linked recessive inheritance is characterized bynever being passed on from father to son, since fathers give their sons their Y chromosome. Also, all affected males in a family are related through their mothers and the trait or disease is typically passed from an affected grandfather, through his carrier daughters, to half of his grandsons.
2. Why does a son never inherit his father’s defective X chromosome?
   A son never inherits his father’s defective X chromosome because they only inherit the father’s Y chromosome which determines that the child develops as a boy.
3. What is required for a woman to display a sex-linked recessive trait?
   For a sex linked recessive trait to be displayed, the pressence of a Y chromosome is required. Since women do not have a Y chromosome they can only be carriers of the trait.
4. What is the chance that Mrs. Smith carries the gene for factor VIII deficiency? Calculate the probability that she will pass it to her offspring. Will male children be affected in a different way than female children?
   There is a 50% chance that Mrs. Smith carries the gene for factor VIII deficiency and there is a 25% chance that her female offspring is a carrier. There is a 25% cance that she will have an unnaffected female offspring and 50% chance of having an unaffected male offspring.
5. What is the chance that Mr. Smith carries the factor VIII gene? Can he pass the gene on to his sons? His daughters? How will each be affected?
   There is no chance that Mr. Smith carries the factor VIII gene; he is not affected either. Accordingly, he cannot pass the factor VIII gene to his offspring.