Whole-genome sequencing reveals the fga exon 6 polymorphism in the AB × TL genetic background. (A) Frequency of homozygous markers moving across the genome in 3 million base-pair intervals identifies a major peak on chromosome 1 in the region of the fga locus. The circle size represents the number of informative markers in that interval. Circles with the number 250 represent a range from 250 to 4500, for easier visualization. (B) Integrative Genomics Viewer (IGV) visualization of whole-genome sequencing data for fga exon 6. The arrow indicates the site of the GGGG/GGG exon 6 polymorphism; male is heterozygous and female is homozygous GGG. Read coverage is >20 for the entire region. (C) AB × TL fish hybrids that are not homozygous for the exon 6 (3G) polymorphism display rapid vessel occlusion of the PCV in response to laser injury. Offspring produced from group matings of parents with mixed fga genotypes were subjected to laser injury and TTO analysis, followed by genotyping. Larvae homozygous for the 3G polymorphism displayed an increased TTO. fga^4G/4G, fga^4G/3G, and fga^3G/3G indicate fga exon 6 GGGG or GGG alleles, respectively. ****P < .0001 when the data from bracketed groups were compared in a Mann-Whitney U test.