Dunaliella salina - Overview

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                 Dunaliella salina Dunaliella salina is a unicellular microalgae belong to division Chlorophyta . It is found in salinity environments such as salted brines, salt evaporation ponds, and hypersaline lakes  .It is able to tolerate varying NaCl concentrations, ranging from 0.2% to approximately 35% . Thus, Dunaliella salina is a hyper-halotolerant organism found in high densities in saline lakes.  The ability to tolerate high salt concentrations is advantageous, since competition is minimal in high salt concentration areas.  How D.salina   tolerate high salt concentration? D. salina has adapted to survive in high salinity environments by accumulating glycerol to balance osmotic pressure. Note :  D. salina is also adapted to solar radiation using β-carotene to protect against ionizing energy.                 Red Colour of Salt Brines  Dunaliella salina...
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Genetics(Part3)

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***Reciprocal cross: When source of gametes is reversed.

                                  Male   × Female
                                    TT             tt
Gametes                      T,T             t,t
F1 generation:             Tt( all are tall)


Now,sex is reversed
                                   Male  × Female
                                    tt             TT
Gametes                    t,t             T,T
F 1 generation:         Tt (all are tall)

**No change in autosomal nuclear traits(Genes present in nucleus)
**Result changes for Sex linked traits,Cytoplasmic traits.


****Back cross:  When F1 hybrid is crossed with either of its parents.It have 2 types:
(a)Out cross: When F1 hybrid(heterozygous) is crossed with itsdominant parent (homozygous dominant).

                               Male ×Female
    (F1 hybrid)       Tt      × TT(dominant parent)
    Gametes            T,t            T,T

   .progeny              TT,  TT,   Tt,   Tt
Phenotypic ratio:   All are tall
Genotypic ratio:      TT  :Tt
                                   1    :1
(b)Test cross: When  F1 hybrid (hrterozygous)is crossed with its recessive parent(homozygous recessive),then cross is test cross.
   ***Used to determine the genotype of dominant individual whetherbit is homozygous or heyerozygous.
                        Male    ×Female
                        Tt         ×   tt  (recessive parent)
Gametes        T,  t            t, t
 
progeny:         Tt,  Tt  , tt,  tt
Phenotypic ratio:  Tall : Dwarf
                                   1   :  1
Genotypic ratio:     Tt    : tt
                                   1    :  1

                        Male   × Female
(F1hybrid)       TT       ×    tt
Gametes         T, T            t,  t

progeny:          Tt,  Tt,  Tt,  Tt
phenotypic ratio:  All are tall
Genotypic ratio:   Onyl one genotype


**** Exception of Law of Dominance:

1)Multiple allelism- 
*When more than 2 alleles present for a gene.
*Alleles are polymorphic forms of each other formed due to mutation.
*Can be observed in a population since diploid organism can maximally have 2 alleles for a gene pair.
*Examples:  ABO blood grouping in humans(3alleles),Coat colour in rabbit(4 alleles),Eye colour in Drosophila(12-15 alleles),Self incompatibilty in plant(3-5 alleles.
* Number of genotypes:n/2×(n+1)
where n is number of multiple alleles.
 ABO blood grouping:  3 alleles
iA,iB and iO (No antigen)
Number of genotypes: 3/2×(3+1) =6

2)Co-Dominance:
*When F1 hybrid resembles both theparents.
Examples: Heterozygous for sickle cell anaemia,Coat colour in cattles,ABO blood grouping in humans.
AB blood resemble to both of the parents have both antigen A and B.

3)Incomplete Dominance:
* When F1  hybrid does not resemble any of the parent instead of this, it shows phenotype for which thete is no alleles.
Reported by Carl Corrensce
Examples: In Antirrhinum majus(Snapdragon)
Mirabilis  jalapa(4 O' clock plant)

Expalnation of concept of Dominance,Incomplete Dominance and Co-Dominance:
*Allele is alternate,contrasting and polymorphic form of a gene.
*A segment of DNA coding for a particular protein(Enzyme/product)
*Various type of a gene develop due to mutation in wild type of allele.
Wild type or unmodified allele:
Already present in population/species.May be dominant,codominant and incomplete dominant.Always produces normal enzyme.
Modified Allele: Develop from wild type of allele via. mutation .May produce:
a) Normal or less efficient enzyme 
b)Non-functional enzyme
c)No enzyme

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