A17-year-old high school senior presents to the clinic in acute respiratory distress. between shallow breaths he states he was at home finishing his homework when he suddenly began having right-sided chest pain and severe shortness of breath. he denies any recent traumas or illnesses. his past medical history is unremarkable. he doesn't smoke, but drinks several beers on the weekend. he has tried marijuana several times but denies any other illegal drugs. he is an honour student and on the basketball team. his parents are both in good health. he denies any recent weight gain, weight loss, fever, or night sweats. examination shows a tall, thin young man in obvious distress. he is diaphoretic and breathing at a rate of 35 breaths per minute. auscultation reveals no breath sounds on the right side of his superior chest wall. on percussion he is hyperresonant over the right upper lobe. with palpation he has absent fremitus over the right upper lobe. what disorder of the thorax or lung best describes his symptoms?

an individual’s sex (i.e., whether they are a male or female) is determined by the sex chromosomes. most people have two sex chromosomes, one that is inherited from their mother and one that is inherited from their father. typically, females have two x chromosomes (xx) and males have one x chromosome and one y chromosome (xy). conditions caused by changes (“mutations”) in genes located on the x chromosome are considered x-linked.

x-linked recessive inheritance

most x-linked conditions are recessive. this means that in a person with two x chromosomes (most females), both copies of a gene (i.e., one on each x chromosome) must have a change or mutation whereas in a person with one x chromosome (most males), only one copy of a gene must have a mutation. a female with a mutation in one copy of a gene on the x chromosome is said to be a “carrier” for an x-linked condition. a male with a mutation in a gene on the x chromosome is typically affected with the condition. because females have two copies of the x chromosome and males have only one x chromosome, x-linked recessive diseases are more common among males than females. however, x-linked recessive diseases can occur in both males and females.

for x-linked recessive disorders, an unaffected carrier mother who has a mutation in a gene on the x chromosome can transmit either the x chromosome with this mutation or a “normal” x chromosome to her children. if the father is unaffected, none of her daughters will be affected and all of her daughters will be unaffected—since they will inherit at least one normal x chromosome from their father. however, each daughter will have a 50% chance of being an unaffected carrier like her mother and a 50% chance of both x chromosomes being normal.

digestion

it excretes wastes