Genetics: Analysis of Genes and Genomes: Keyword Hot Links for chapter 8

Many people think that birth defects are rare and happen only to other people. But about 4–5 percent of all newborns have some type of birth defect, amounting to 150,000 cases each year in the United States alone, and birth defects are the leading cause of infant death and disability. Some 3,000–5,000 different birth defects have been described. The most common are listed at this keyword site. The list includes only those conditions that can be diagnosed immediately at birth, and does not include such conditions as cystic fibrosis, Tay-Sachs disease, or sickle-cell anemia, which only become apparent in the first weeks or months after birth. Note that defects of the heart and circulatory system affect more infants than any other type of birth defect.

About half a million human karyotypes are analyzed every year in North America in the course of genetic diagnosis and genetic counseling. At this keyword site you can arrange and analyze digital images of human chromosomes from actual patients, then draw your own conclusions much as you would if were you carrying out genetic analysis in a hospital or clinical setting.

Molecular studies of the red and green opsin genes indicate abnormalities in 15.7 percent of Caucasian men. This frequency is substantially smaller than the incidence of color blindness as shown by color-vision testing, which suggests that some chimeric genes created by unequal crossing-over may be compatible with normal color vision. More information about the molecular genetics and physiology of color vision can be found by searching the two keyword sites protanopia and deauteranopia. You will also find a description of the "Nagel anomaloscope" used in testing color vision.

Down syndrome affects more than 350,000 people in the United States, with approximately 5,000 new cases every year. There are many myths about the condition. One is that people with Down syndrome are severely retarded, another is that their parents are usually old. At this keyword site you can find these and other myths and the truths that contradict them.