What types of monogenic traits are in humans?
• There are 70,000 to 100,000 genes in a human genome. • A human genome is the collection of all genes in all chromosomes present in an egg or sperm. • Of these, about 5000 have been identified and associated with clinical disorders. • Monogenic traits may be recessive or dominant depending on their function in the human life cycle. • In general recessive disorders represent a loss of a normal function. • In general dominant disorders represent a developmental defect in gene expression (they tend to mess up the way the embryo forms). • How do recessive disorders work in humans? • With rare exceptions, the two parents of a child with a homozygous recessive disorder are both normal in appearance. The two parents are each heterozygous. Thus the parental generation for the normal parents giving rise to a child who is an albino would be represented as: P1 Aa x Aa • Mendel’s law of segregation predicts a 3 to 1 phenotypic ratio of 3 normal to one albino offspring from such a cross. • We can
