Genetics of Fishes Basic Genetics w Most fish
Genetics of Fishes
Basic Genetics w Most fish are diploid (2 N) w Normal for most vertebrates w ~50 chromosomes typical (range 16446) w Produce haploid (1 N) gametes
Basic Genetics w Constant chromosome number usually characteristic of a species w Some species may display variation w Rainbow trout - 58 -64 chromosomes w Variation results when chromosome arms rearrange
Mendelian Inheritance w Alleles, homozygous, heterozygous w Dominant, recessive w Normal pigmentation dominant (AA or Aa) w Albinism recessive (aa)
Partial Dominance w Siamese fighting fish color w Heterozygotes distinguishable from homozygotes w One homozygote is steel blue w Heterozygote is blue w Other homozygote is green
Polyploidy w Duplication of entire chromosome set w Possibly from failure in one cell cycle of cell division in early embryo w Triploid w Tetraploid
Polyploidy w Autopolyploidy embryo from parents of the same species w Allopolyploidy embryo from parents of different species
Polyploidy w Species in Salmonidae probably descended from autotetraploid ancestor w Species in Catostomidae probably descended from an allotetraploid ancestor
Oriental (weather) loach Misgurnus anguillicaudatus w Naturally occurring: w Diploids (50 chromosomes) w Triploids (75 chromosomes) w Tetraploids (100 chromosomes)
Induced Polyploidy w Can use various “processes” to induce polyploidy in some species w Heat shock w Cold shock w Pressure shock w Some chemical, antibiotic treatments
Induced Polyploidy w Disrupt end stages of meiosis just after fertilization by sperm w 2 N from egg + 1 N from sperm = 3 N triploid w 2 N from female w 1 N from male
Induced Polyploidy w Disrupt one of early cleavage divisions after normal fertilization w 2 N + 2 N = 4 N tetraploid w 2 N from female w 2 N from male
Typical Applications w To produce sterile fish (odd ploidy messes with normal meiosis) for a variety of uses w Grass carp to control unwanted vegetation in lakes and ponds
Typical Applications w Aquaculture - penreared Atlantic salmon may have inefficient feed transfer if energy is devoted to egg/sperm production w Polyploid salmon may not mature - all feed into growth
Typical Applications w Trophy fishery w Experimental releases of triploid Chinook salmon into Great Lakes to produce nonmaturing, trophy-sized fish that won’t disrupt wild gene pools
Problems w “Nature finds a way” w Despite expected sterility of polyploid fishes, some fish may produce viable haploid gametes and reproduce w May result in a diploid population
Hybridization w Can occur naturally w Congeneric species in sympatry w Either natural, or because of introductions w Shiners often hybridize
Hybridization w Sunfishes w The genus Lepomis w Many different combinations
Hybridization w Crappies
Hybridization w Black basses w The genus Micropterus w Spotted bass X smallmouth bass
Hybridization w Cutthroat trout X rainbow trout w Losing genetic integrity of cutthroat populations w Introgression
Hybridization w Brook trout X brown trout w Tiger trout
Hybridization w Artificial manipulation for fast growth w Saugeye w Sauger X walleye
Hybridization w White bass X striped bass w Freshwater species and anadromous species w New fishery for large reservoirs
Hybridization w Tiger muskie w Northern pike X muskellunge w Sport fishery and forage management in lakes lacking pike
Hybridization w Hybrids typically sterile - problem with chromosome alignment during meiosis w Not always the case w Hybrids may show better vigor, faster growth
Sex Determination w 10 sex-determining systems in fishes w Most fish (e. g. , salmonids) are like humans w Male is heterogametic - XY w Female is homogametic - XX
Sex Determination w Some fishes have an alternative sexdetermining system more like that of birds (e. g. , some platies and some Tilapia spp. ) w Female is heterogametic - WZ w Male is homogametic ZZ
Sex Determination w Southern platy w Gender determined by combination of X, Y, and Z chromosomes
Environmental Sex Determination w Sex determined solely by sex chromosomes in most fishes w Produces sex ratio of 1: 1 w Some species may have additional autosomal chromosomes involved in sex determination
Environmental Sex Determination w The sex of the Atlantic silverside is controlled by both genotype and water temperature w Temperatures experienced by larvae 30 -45 days after hatching strongly influence gender w Cold temps. - females w Warm temps. - males
Transgenic Fish w Inserting genes from other organisms into fish to improve “performance” w http: //www. youtube. com/watch? v=f. Vx 9 m 3 uc. Gc. Y
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