The fourth week after conception, growth is rapid. the neural tube along a baby's back is closing and the baby's heart is pumping blood. if this neural tube does not close properly, a condition called may result. a) fragile x b) spina bifida c) cleft palate d) down's syndrome

THe correct answer is B. Spina bifida.

Explanation

Neural tube or NTD defects are birth defects of the brain and spinal cord. These defects change the shape or function of one or more parts of the body. Also, they can cause problems in general health, and the development or functioning of the body. These defects occur in about 3,000 pregnancies per year in the United States. One of the most common NTDs is spina bifida in which the tiny bones of the spine do not close completely, and a part of the spinal cord sold by the spine. Children with spina bifida lose mobility of the legs and problems with bladder and bowel control that make it difficult for them to go to the bathroom to meet their physiological needs. So, the correct answer is B. Spina bifida.

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.