When a leaflet is touched, this triggers an action potential in sensing cells at the base of the leaflet. cells at the base of the leaflet respond to this action potential, folding the leaflet inward. if you make a gentle touch that only stimulates the end leaflet, the resulting action potential propagates down the axis that supports all of the leaflets, triggering an action potential in the sensing cells at the base of the adjacent leaflet, then the one next to it, and so on down the line, similar to how electrical signals propagate in the human nervous system. you can watch the progress of this pulse of action potential by watching adjacent leaflets fold inward, one after another. if, instead of a touch, a leaf structure is stimulated with a spark that sends a charge through the structure that holds all of the leaflets, how might you expect the leaflets to behave?

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.