KASHMEERA.N.AKASHMEERA.N.A

III SEM MSc ZOOLOGYIII SEM MSc ZOOLOGY

ROLL NO:37ROLL NO:37

CHRIST COLLEGECHRIST COLLEGE

KASHMEERA.N.AKASHMEERA.N.A

III SEM MSc ZOOLOGYIII SEM MSc ZOOLOGY

ROLL NO:37ROLL NO:37

CHRIST COLLEGECHRIST COLLEGE

SelectionSelection

PrerequisitesPrerequisites

GoalsGoals

MethodsMethods

Successive choosing of the best varieties from the available lot by nature or man.

The aim of a breeder - to get maximum profit possible

the genetic worth of the stock by selection.

Based on a single desirable trait or combination of traits.

growth rate, by better utilization of food growth rate, by better utilization of food natural food in ponds ; food mixturesnatural food in ponds ; food mixtures

resistance to deviations from the normal environmental resistance to deviations from the normal environmental conditions - oxygen deficiency, conditions - oxygen deficiency, high or low temperature,high or low temperature, higher salinity etchigher salinity etc

resistance to infectious diseases resistance to infectious diseases to infestation with parasites to infestation with parasites

the nutritive properties of fish.the nutritive properties of fish.

1. Specifically define - the breeding goal i.e. the trait under selection

2. The entire life cycle of the animal should be under control.

3. It should be possible to hold and individually evaluate a number of generations in identical rearing systems.

4. Establish relative economic value of the traits that are to be selected

5. For the selected traits, the phenotypic (VP) and genetic variances (VG), heritabilities etc should be known. VP = VG + VE

Mass selectionMass selection

Genotypic selectionGenotypic selection

Family selectionFamily selection

Sib – selectionSib – selection

Selection by progeny testingSelection by progeny testing

Combined selectionCombined selection

• Character/ Individual selection

• Individuals selected from mixed population

on the basis of phenotype.

• Genotype may be unknown.

Response (R) = i x σ x h2 = S x h2

• i = intensity of selection

• = degree of variation in the trait

• h2 = heritability

• S = Selective differential

• Response α heritability

• h2 = R/S

METHODS TO RESPONSEMETHODS TO RESPONSE

• i / i / σσ / h / h22

• ↑ ↑ intensity of selection(i)intensity of selection(i) ↑ ↑ no. of individuals grown → ↑↑ severity of

selection

• Variability (Variability (σσ ) ) ↑↑

only genetic variation important envtal - useless - ↓ heritability

Heritability ( h2 )

• Outbreeding – cross non related individuals → ↑degree of heterozygosity i.e. ↑ in genetic variation

• Inbreeding ↑ homozygosity

ADVANTAGES OF MASS SELECTIONADVANTAGES OF MASS SELECTION

• Simplest & common method

• Characteristic to be improved easy to measure

• Can be used efficiently in selection

for growth rate

for age at maturity

• To overcome disadvantages of mass selection

• include – family selection

progeny testing

• For selection of characteristics of low heritability - survival,

meat quality,

age at maturation

• Families grown in identical conditions

↓

Compare & select best

Response eq. ~ mass selection ~ • Rf = if x f x h2

f

• i < mass selection – not possible to grow large no. of families.

• reduction in - denotes variation in family

not individual variation

• h2 much higher

• If individuals from best family sacrificed for examination – use brothers & sisters for breeding

• Use full & half siblings

• Advantage – generation interval not ↑ like mass selection

• Disadvantage – each family - separate tank - marking difficult - envtal & tank effects on characters b/n families.

• Enables assessment of breeding qualities of separate spawners/pairs of spawners & selection of best

• 3 methods

I.Testing pairs (not separately)

II. ,, spawners of one sex

III. ,, both ♀♀ & ♂♂

Advantage of PT

• permit evaluation of separate spawners & selection of best

• Mass selection more efficient

• Genotypic selecton advantageous for certain characters – fat content

• For characters like weight – combined selection

• CS sum up efficiencies of mass & genotypic selection in short time.

CS consist of:

• Performing mass selection amoung fingerlings

• Progeny testing of males

• Family selection with simultaneous breeding of 5-10 families

• Repeated performance of mass selection in the best families

It is the technique of breeding of fishes of two species or genera which It is the technique of breeding of fishes of two species or genera which ordinarily do not breed.ordinarily do not breed.

Fish - external fertilisation - Fish hybridizes more frequently than Fish - external fertilisation - Fish hybridizes more frequently than tetrapodes tetrapodes

Naturally hybridized fishes - Cyprinidae , Salmonidae etcNaturally hybridized fishes - Cyprinidae , Salmonidae etc

Hybridization - Hybridization - ↑ ↑ hybrid vigour / heterosishybrid vigour / heterosis

Hybrids – fertile/sterile – must be verified before introducing to natural Hybrids – fertile/sterile – must be verified before introducing to natural envt.envt.

Indiscriminate hybridization Indiscriminate hybridization →→ contamination of genepool. contamination of genepool.

Interspecific & intergeneric hybridizationsInterspecific & intergeneric hybridizations

Labeo rohita female Labeo calbasu

produced by mating between two different species in same genus.

In India mating female kalbasu and Labeo rohita was highly successful.

Over 94% fertilisation was obtained.

The growth rates of hybrids are superior to the parent Kalbasu.

It attains maturity in two years.

INTER SPECIFIC HYBRIDIZATIONINTER SPECIFIC HYBRIDIZATION

INTER GENERIC HYBRIDIZATIONINTER GENERIC HYBRIDIZATION

• male and female are selected from different genera

• Catla catla Labeo rohita

• Inter generic hybrids between Catla and Rohu attains full maturity in 3yrs

.

Labeo rohita Cirrhinus mrigala

Intergeneric hybridizationIntergeneric hybridization

Crossing between Rohu and Mrigal is more successful Crossing between Rohu and Mrigal is more successful and 90% fertilisation is done andand 90% fertilisation is done and

hybrids attain full maturity in 2yrs and hybrids attain full maturity in 2yrs and

showed intermediate charactershowed intermediate character

Intergeneric hybridizationIntergeneric hybridization

Cirrhinus mrigala Labeo calbasu

Mrigal-Kalbasu hybrids attain full maturity within 2-3yrs. Mrigal-Kalbasu hybrids attain full maturity within 2-3yrs.

These hybrids are also capable to produce new ones. These hybrids are also capable to produce new ones.

• In fish farming, if proper care is not taken the fishes can breed with their close relatives or same parental generation – INBREEDING

• cause early mortality of fish, poor growth rates and other genetical abnormalities – INBREEDING DEPRESSION

• Inbreeding →reduction of desirable traits and fertility.

• If a farm based on limited number of population of brood stocks the progeny over long periods can face inbreeding problems.

The advantage of inbreeding:

• Production of inbreed lines are useful in improvement of stock

• To produce pure lines of fish

Pure lines of strains are used for perfect hybridization of fish to obtain favourable heterosis, monosex.

· Pure lines help in gene mapping

· To determine

1. Phenotypical variations2. Extent of inbreeding depression3. chromosomal makeup to the fish

Crossbreeding is the solution of inbreeding depression,

the fishes are allowed to breed with different breed varieties, strains or genotypes of farmed species

the aims of cross breeding

to achieve

· Better growth rate· Better desired qualities· Increase the survival rate

• lower the early stage mortality

· By chromosomal manipulation – Gynogenesis or Androgenesis

· Hormonal manipulation – Feminisation or Masculisation

· By genetic engineering – trangenesis or mutation

GynogenesisGynogenesis

• process to produce individuals from maternal chromosomes only eventually to process to produce individuals from maternal chromosomes only eventually to obtain homozygosity. obtain homozygosity.

• Parthenogenetic devpt of eggs after activation with genetically inert spermParthenogenetic devpt of eggs after activation with genetically inert sperm

• Gynogenesis in fish farming is used to form inbred lines to achieve proper Gynogenesis in fish farming is used to form inbred lines to achieve proper hybridization and selective breeding.hybridization and selective breeding.

Methods:Methods:

Sperm nucleus is inactivated prior to fertilization by use of X-Rays, chemicals – Sperm nucleus is inactivated prior to fertilization by use of X-Rays, chemicals – dimethyl sulphate.dimethyl sulphate.

• eggs are exposed to sub lethal temperature shocks before or after fertilization - eggs are exposed to sub lethal temperature shocks before or after fertilization - suppress the meiotic divisions of eggs i.e. ensuring the non reduction of nuclear suppress the meiotic divisions of eggs i.e. ensuring the non reduction of nuclear components.components.

• Upon fertilisation the resulting diploid individuals retain the second polar body Upon fertilisation the resulting diploid individuals retain the second polar body nucleus (maternal) besides the egg nucleus,nucleus (maternal) besides the egg nucleus,

gynogenesis- preventing the extrusion of second polar body

nn 2nd polar body

EggActivation – irradiated sperm

2n

Shock treatment and retention of 2nd polar body

Homozygous diploidGynogenetic progeny

•In India Gynogenesis are tried on Indigenous as well as Exotic carps.

•Eggs of rohu are fertilised with irradiated sperms of Catla and then exposed to cold 12°C and heat 39°C shocks to obtain gynogenetic rohu.

ANDROGENESISANDROGENESIS

• Development of an organism with only paternal genes

• androgenesis is development of an embryo from a fertilised egg from which the nucleus has been removed.

• The embryo therefore contains only paternal genes.

The method of dispermic androgenesisdispermic androgenesis, developed for sturgeon fishes, includes genetic inactivation of eggs, their insemination with concentrated sperm (to cause polyspermy), and heat shock to facilitate the fusion of male pronuclei.

The restoration of the diploid state of androgenotes by fusion of two sperm nuclei allows androgenetic progeny to have a heterozygosity level similar to that in a regular crossing.

endangered sturgeon fishes may be recovered by means of dispermic androgenesis if the sperm alone of a given species is available.

Mono Sex Culture

Mono Sex Culture

Mono-sex culture is based on the culture of fish by producing all males or all females

depending upon the sex which have better food conversion ratio and growth rate.

Experimental hybridization in Tilapia can produce monosex stock

Treatment with sex hormones : sex reversal

Necessity of Monosex Culture

Some time one sex of certain species has better growth rate and food conversion efficiency.

To culture that sex (male/female) monosex culture is essential.

For example - male Tilapia grows faster than female -culture of male is beneficial in case Tilapia.

Transgenic Fish Transgenic Fish

• A transgenic fish is one which carries one A transgenic fish is one which carries one or more than one foreign genes. or more than one foreign genes.

• The foreign genes are selectively The foreign genes are selectively incorporated by micro injection into the incorporated by micro injection into the egg egg → → transgenic fish.transgenic fish.

• Fish transgenies are difficult because of tough egg-chorion which Fish transgenies are difficult because of tough egg-chorion which impedes microinjection.impedes microinjection.

• A prior puncture or use of micro pile (an opening in the egg surface A prior puncture or use of micro pile (an opening in the egg surface for sperm entry during fertilisation) has to be made for for sperm entry during fertilisation) has to be made for microinjection. microinjection.

• The micropile is made by or by using trypsin digestion. The micropile is made by or by using trypsin digestion.

• The gene can be transferred by electroporation (exposing the egg The gene can be transferred by electroporation (exposing the egg chorion in an electric shock for a fraction of second) or by retroviral chorion in an electric shock for a fraction of second) or by retroviral injection. injection.

• The foreign gene then transferred into the nucleoplasm or the The foreign gene then transferred into the nucleoplasm or the cytoplasm.cytoplasm.

• In case of retroviral injection, the genes are first incorporated into In case of retroviral injection, the genes are first incorporated into the viral genome, and then through the virus the gene are the viral genome, and then through the virus the gene are transferred into the host by injection. transferred into the host by injection.

• · The fish of superior quality or desired The fish of superior quality or desired traits are produced by this process. traits are produced by this process.

• Giant sized fish or super fish can be Giant sized fish or super fish can be produced. produced.

• This can be achieved by incorporating the This can be achieved by incorporating the growth promoting genes – bovine growth growth promoting genes – bovine growth hormone gene or human growth hormone hormone gene or human growth hormone gene gene

GM Zebra fish

Centre for Cellular and Molecular Biology (CCMB) Centre for Cellular and Molecular Biology (CCMB)

CCMB fish are CCMB fish are auto-transgenicauto-transgenic, meaning the genes inserted into a , meaning the genes inserted into a fish’s genome are a mashed-up cocktail of its own genome.fish’s genome are a mashed-up cocktail of its own genome.

not importing genes from an alien species, not using DNA from even a not importing genes from an alien species, not using DNA from even a related species. related species.

There are no foreign genes involved. Therefore, it’s unlikely that mere There are no foreign genes involved. Therefore, it’s unlikely that mere genetic modification could produce a toxic protein, genetic modification could produce a toxic protein,

the synthesized gene stimulates production of a growth hormone that the synthesized gene stimulates production of a growth hormone that makes the fish bigger and grow faster, makes the fish bigger and grow faster,

GENETICALLY MODIFIED ROHUGENETICALLY MODIFIED ROHU