ABSTRACT

We inherit the information required to produce all our characteristics in the form of DNA. We do not inherit the characteristicsonly the information to produce them. The rules of inheritance are simple. We inherit half our genetic material (DNA) from each parent. The production of sperm and eggs that occurs in parents’ gonads results in the production of gametes that carry only half of the DNA that made the parents unique. When the egg and sperm unite at fertilization, a new, unique individual is created. Like her parents, this individual, if female, has two copies of all the genetic material and she can produce eggs that will contain only one copy of each gene. If the child is male, he, too, has two copies of each gene but can also pass only one of the two to each of his progeny. Most cells contain a nucleus made up of chromosomes. Normally we all have 23 pairs of chromosomes including the gender chromosome called the XY chromosome. Why pairs? For each chromosome, we inherit one from our mother and one from our father. If we are female, we will inherit an X from both parents. If we are male, we will inherit one X and one Y chromosome (Figure 16.1). Nuclear DNA is found in our chromosomes. Where are our chromosomes? Our chromosomes can be found in cells with nuclei throughout our bodies. Nuclear DNA

comes from nucleated cells: skin cells, spermatozoa, and white blood cells. Mature red blood cells, although important, do not have a nucleus (Figures 16.2-16.4).