Key Concepts of Section 6.4

• Inherited diseases and other traits in humans show three major patterns of inheritance: autosomal dominant, autosomal recessive, and X-linked recessive (see Figure 6-32).

• Genes for human diseases and other traits can be mapped by determining their co-segregation with markers whose locations in the genome are known. The closer a gene is to a particular marker, the more likely they are to co-segregate.

• Mapping of human genes with great precision requires thousands of molecular markers distributed along the chromosomes. The most useful markers are differences in the DNA sequence (polymorphisms) between individuals in noncoding regions of the genome.

• DNA polymorphisms useful in mapping human genes include single-nucleotide polymorphisms (SNPs) and short tandem repeats (STRs).

• Linkage mapping can often locate a human disease gene to a chromosomal region that includes as many as 10 genes. To identify the gene of interest within this candidate region typically requires expression analysis and comparison of DNA sequences between wild-type and disease-affected individuals.

• Some inherited diseases can result from mutations in different genes in different individuals (genetic heterogeneity). The occurrence and severity of other diseases depend on the presence of mutant alleles of multiple genes in the same individual (polygenic traits). The genes associated with such diseases can be mapped by finding a statistical correlation between the disease and a particular chromosomal location in a genome-wide association study.