Zebrafish “Primer”
BiologyGeneration time: 3–4 months Number of offspring per cross: ∼100 Size: 3–4 cm Time to develop to hatchling stage: 3 days Life span: 2 years
Genome and GeneticsHaploid genome size: 1.7 × 109 bp Number of chromosomes: 25 (metacentric) Linkage map: 2900 cM Number of characterized mutations: ∼2000 Strains: Wild-type strains in most common use are AB, TubAB, TupLF, WIK, and SJD. Interstrain polymorphism is variable; AB/SJD are ∼50% polymorphic for SSLPs Current no. of mapped markers: 652 RAPDs, 703 SSLPs Current no. of mapped mutations: ∼15 Current no. of mapped cloned genes: ∼150 ESTs: >3000
Genetic analysis—Special Tricks Gynogenetic haploids: Eggs fertilized by UV-inactivated sperm develop as haploids to the end of the embryonic stage. Polymorphic DNA markers can be mapped by following their segregation in the haploid offspring of a heterozygous female resulting from a cross between two different zebrafish strains.
Gynogenetic half-tetrad diploids: Pressure treatment of an egg fertilized by inactivated sperm inhibits the second meiotic division, leading to the development of diploid embryos. In these embryos, which mostly survive to adulthood, chromosomes that have recombined (there is usually only one crossover per chromosome in zebrafish) are homozygous at loci centromere-proximal to the crossover site, and heterozygous for loci distal to the crossover. Thus, any embryos homozygous for a recessive mutation will be homozygous for the centromeric region linked to the mutation. Pools of such embryos will harbor only one allele of the relevant centromere, whereas they will contain mixtures of centromere-linked alleles for each of the other chromosomes. Thus, in principle, 25 PCR reactions (1 for each centromere) performed on each of two DNA pools, one derived from gynogenetic mutant embryos and the other derived from gynogenetic wild-type embryos, will indicate the chromosome that carries the mutation. In addition, the frequency of homozygous mutants observed among these progeny will indicate the approximate genetic distance between the mutation and its centromere, which can be readily confirmed by subsequent marker analysis.
Gynogenetic diploids: Heat treatment of haploid embryos at the one-cell stage generates diploid embryos homozygous at all loci, which can be used to obtain clonal lines of fish.
