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Genetics Terms. Selective breeding -the choosing of individuals of a single strain and spp. Hybridization -the crossing of different spp. Crossbreeding -the mating of unrelated strains of the same spp. to avoid inbreeding. Selective Breeding.

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genetics terms
Genetics Terms
  • Selective breeding-the choosing of individuals of a single strain and spp.
  • Hybridization-the crossing of different spp.
  • Crossbreeding-the mating of unrelated strains of the same spp. to avoid inbreeding
selective breeding
Selective Breeding
  • “Artifical selection” as opposed to natural selection, results in reducing genetic variability in a population. Could be considered inbreeding if not closely monitored.
  • If selective breeding involves excessive inbreeding physical abnormalities, metabolic deficiencies, and developmental abnormalities may occur.
  • Inbreeding depression-loss of fitness due to inbreeding
    • more likely to observe occurence of recessive traits
    • Decrease in heterozygosity
selective breeding1
Selective Breeding
  • Although potential for deleterious results, selective breeding rationalized by:
    • size
    • color
    • shape
    • better FCR
    • reproductive capacity
    • disease resistance
hybridization
Hybridization
  • Already looked at hybrid striped bass.

What other examples are out there??

Splake-brook trout/lake trout, Tiger Musky-northern pike/musky

Sunfish hybrids (many combinations)

  • Hopefully achieve “hybrid vigor,” at least in some trait.
  • Most true hybrids are sterile, but not all.
gynogenesis
Gynogenesis
  • Development of an ovum without fusion of gametes
    • usually haploid and die
    • sometimes diploid larva develop
      • requires retention of 2nd polar body during meiosis
      • Amazon mollies, cruzian carp do this
  • Induced by:
    • radition, chemical, electrical currents, sperm from related species
slide7

Mono-sex male tilapia populations can be produced by:

  • Visual selection

2. Hybridization

3. Sex-reversal

4. Genetic manipulation

Male Populations

using two species
Using Two Species
  • Two species of tilapia can be crossed to yield all-male offspring.
  • Male Hornorum tilapia can be hybridized with the female Nile tilapia and offspring are all-male.
  • However, the hybrid is fertile and can backcross with female Nile and Hornorum tilapia.
using two species1
Using Two Species
  • Only genetically pure Hornorum and Nile tilapia will result in 100% male offspring.
  • Maintaining pure lines of Nile and Hornorum tilapia over a long period of time is difficult.
  • Additionally, hybrid fry yield per female is low compared with fry yield from pure species spawns.
slide10

Hybridization

Male Hornorum tilapia

ZZ

XZ

XX

Female Nile tilapia

All-male hybrid tilapia

sex determination by hormones
Sex determination by hormones
  • A popular way to produce all-male populations is with hormone sex reversal of fry.
  • Tilapia fry (18 day) are fed a diet containing a male steroid (methyl testosterone) for 20 to 28 days.
  • Females develop as “functional males” following hormone treatment.
  • All-male populations are hard to produce!!
  • ~95 to 98% males are commonly produced.
slide13

Genetic Manipulation

1) XXF + XYM XX + XY

normal

more genetic manipulation
More genetic manipulation
  • What if female Nile tilapia are homozygous (XX) and male Nile tilapia are heterozygous (XY) for sex.
  • A pairing of genetically normal male and female Nile tilapia will result in 50% male and 50% female offspring.
  • Now if we feed normal fry estrogen for 28 days, we get phenotypic all-female fry.
slide15

Genetic Manipulation

1) XXF + XYM

estrogen

XXF + XY”F”

slide16

Genetic Manipulation

1) XXF + XYM

estrogen

XXF + XY”F”

2) XY”F” x XYM

XXF + 2 XYM + YYM

slide17

Genetic Manipulation

1) XXF + XYM

estrogen

XXF + XY”F”

2) XY”F” x XYM

XXF + 2 XYM + YYM

3) XXFx YYM

100% XYM ??

transgenics how do you get a transgenic fish
Transgenics: How do you get a transgenic fish?
  • Transgenic or genetically engineered animals are developed by inserting single or multiple genes from one species into the DNA of another species.
  • Three basic steps:
    • Isolate and identify the genes that posses the desired trait. Genes may come from similar fish species, plants, bacteria, animals, and even humans.
    • Insert isolated material into the intended target fish’s eggs.
    • Grow your fish!!
slide19
Differences in terms?
  • The terms genetically engineered, genetically modified, and transgenic are used synonymously.
  • The term transgenic arises from the procedure of transgenesis, one method in which scientists have successfully inserted genes from one species to another.
slide21
What is a triploid fish?
  • Triploid fish contain three sex chromosomes.
  • Heat and or pressure applied to females’ eggs to generate the extra chromosome.
  • Proponents of G-EN suggest environmental risks associated with their release into open water would be rendered harmless.
  • No guarantee of sterility!!
  • Competition is a reality for sterile fish too!
polyploidy
Polyploidy
  • Polyploidy has been well-studied in fish and shellfish.
  • Channel catfish triploids become larger than diploids
  • Triploids converted feed more efficiently than diploids (Wolters et al., 1982), had six percent greater carcass yield at three years of age.