, proposed the theory of which suggested the continents move and started out in different positions from what they are currently. In the 1960s, scientists discovered the spreading apart of . This in turn led to the theory of . This theory says that the is made of plates which float on a "plasticlike" undersurface called the asthenosphere. Where these plates come together at their, changes take place in the crust and its feature.

Alfred Wegner proposed the theory of Continental drift which suggested the continents move and started out in different positions from what they are currently. In the 1960s, scientists discovered the spreading apart of the seafloor. This in turn led to the theory of Plate tectonics. This theory says that the earth's outer crust, the lithosphere is made of plates which float on a "plasticlike" undersurface called the asthenosphere. Where these plates come together at their boundaries, changes take place in the crust and its feature.

Explanation:

Alfred Wegner proposed the theory of Continental drift which suggested the continents all continents were once connected in a large single mass that broke apart around 200 million years ago before slowly moving apart to where they are currently.

In the 1960s, Harry Hess, a geologist and Navy submarine commander during World War II, discovered the spreading apart of the seafloor. This in turn led to the theory of Plate tectonics. This theory says that the earth's outer crust, the lithosphere is made of plates which float on a "plasticlike" undersurface called the asthenosphere. Where these plates come together at their boundaries, changes take place in the crust and its feature.

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.