The links at left lead to additional resources to help you learn about the topics in this chapter. These resources include Hot Links to Web sites related to the subject of these topics, the Take It to the Net activities referred to in your textbook, and a Self-Test you can use to test your knowledge of this chapter.
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Section 14-1: Human Heredity
All egg cells carry a single X chromosome (23X). However, half of all sperm cells carry an X chromosome (23X), and half carry a Y chromosome (23Y). This ensures that just about half of the zygotes will be 46XX (female), and half will be 46XY (male).
In both cystic fibrosis and sickle cell disease, a small change in the DNA of a single gene affects the structure of a protein, causing a serious genetic disorder.
Section 14-2: Human Chromosomes
Males have just one X chromosome. Thus, all X-linked alleles are expressed in males, even if they are recessive.
Nondisjunction causes gametes to have abnormal numbers of chromosomes, which in turn causes a chromosome number disorder.
Section 14-3: Human Molecular Genetics
The Human Genome Project is an attempt to sequence all human DNA.
In gene therapy, an absent or faulty gene is replaced by a normal, working gene.