Law of Segregation Or Law of Purity of gametes with example and mechanism of segregation

Law of Segregation Or Law of Purity of gametes :- Given by Mendel→ 

"When a pair of Constrasting characters remained together in F1 hybrid then both of them live together without Contaminating or blending or intermingling with each ather and get Segregated Completely and in pure form during the formation of gametes"

Example and mechanism of segregation-

• when homozygous red flowered plants are crossed with homozygous white flowered plant than parent plant always produce only one type of gammat as they are homozygous genotype that is red flowered plant and white flowered plant produce gametes 'R' and 'r' respectively.

• The gametes of both the plant, after cross pollination, produce F1 hybrid whose genotype is 'Rr' and phenotype is Red.

• Both the genes (R and r) of red and white colour respectively present together in F1 hybrid, but only red colour is expressed because the gene 'R' of red colour is dominant over the gene 'r' of white colour.

• Both the genes (R and r) live together for a long time in F1 hybrid but they do not affect each other. They neither mix together nor contaminate each other.

• During the gamete formation of F1 hybrid, two types of gametes will form in equal number. Half of the gametes will contain gene 'R' sand the other half will contain the gene 'r' .

• During self pollination this gametes  unite together in three possible combinations- 'RR', 'Rr' and 'rr' and two types of phenotypic plants will produce in F2 generation in which 75% are red flower plants and 25% are white flower plants .

• The appearance of white colour in F2 generation shows that gene 'r' of white colour lives together with the gene 'R' of red colour in F1 hybrid but 'r' gene neither mixes with it nor contaminate by it and gets separated from it during the gamete formation.

This law given by Mendel is called "Law of segregation" or "Law of purity of gametes".

Mendel's law of dominance with example

• Law of dominance:- Given by Mendel- "when  two pure homozygous plants taking only one pair of contrasting characters are crossed, only  one  character of a pair  expresses itself in the F1 generation and other is suppressed itself"

In this way, in F1 generation only one type of phenotype is expressed.

The character which is expressed in F1 generation is called Dominant and the character which is suppressed is called recessive.

The "law of dominance" is not universally applicable.

• Example:-

Law of dominance can be explained by monohybrid cross. If a cross is made between pure red flowered plant and pure white flowered pea plant, all plants obtained in F1 generation are Red flowered pea plants, though these plants  contain the genes (Rr)  of both the characters. In the experiment, red colour is dominant character while white colour is a recessive character.

Mendel's Hybridisation experiment

• Mendel selected 22 varieties of pea plant for his experiments.

• Mendel studied  total 7 characters of inheritance in which each character is having two contrasting forms but consider only one contrasting character at a time.

• He took a pure tall pea plant and pure dwarf pea plant and cross pollinated them. that is the pollen grains of tall plant are dusted over the stigma of Dwarf plant and vice versa.

• Plants produce from these generation were all tall.
  

• All plants of first generation were called first filial generation or F1 generation by Mendel.

• Now when tall plants of F1 generation are self pollinated and the seeds obtained  were sown then all plants were not tall but there were dwarf plants also.

• The phenotypic ratio of these tall plants and  dwarf plants was 3:1 that  is 75% plants were tall and 25% plants were dwarf.

• Offsprings obtained from F1 Generation were called second filial generation or F2  generation by Mendel.

• The genotype of 3 tall plants and 1 dwarf plant in F2 generation is

1 Pure Tall (TT)

2 Hybrid tall (Tt)

1 Pure dwarf (tt)

• And the genotypic ratio was 1:2:1

• Mendel drew some conclusions from his experiments:-

1. Whatever may be the parents, reciprocal crosses always gives same results. For example, In original or basic cross between tall male and dwarf female all F1 generation plants were tall and in reciprocal cross between dwarf male and tall female the F1 generation plants  were also tall.
2. Out of two contrasting characters, only one is expressed in F1 Generation and other remain hidden and on self pollinating plants of F1 generation, the hidden characters will reappeared in F2 generation.
3. This experiment all revealed that the dwarf character only remain hidden in F1 generation but not completely disappeared because they reappeared in F2 generation.

• Traits which appeared in F1 generation are called Dominant characters and the characters which is hidden in F1 generation and reappeared in F2 generation is called recessive character.

Polymerase chain reaction notes- definition, principal, requirements, mechanism

Introduction of PCR-   The polymerase chain reaction was developed by an American biochemist Kary Mullis in the year 1983. By Using PCR it is possible to generate thousands to millions of copies of a particular section of DNA from a very small amount of DNA

• Definition-

 Polymerase chain reaction (PCR) is a lab  techniques of gene amplification with the help of which identical Copies of desired DNA can be Synthesized within a time of short duration.

• Principle of PCR-   

Principle of PCR is based on the ability of DNA polymerase to synthesize new strand of  DNA Complementary to the offered template strand Because DNA polymerase can add a nucleotides only onto the  preexisting -OH group, at the end of the reaction billions of copies are formed.

• Requirements :- 

1. DNA template: Any Source that contains one or more target DNA molecule to be amplified can be taken as DNA template.
2. Taq polymerase -PCR requires a DNA Polymerase enzyme that makes new Strands of DNA using strands as templates. The DNA polymerase used in PCR is Taq polymerase which is isolated from a thermostable bacterium called Thermus aquaticus. It lives in hot Spring and very stable and is  most  active around  70 degree Celsius.Primers- Taq Polymerase can only make DNA when  it is given a primer.
3.  Primer is a very short sequence of nucleotides which provide a starting point for the synthesis of DNA.
4. Two 15-35 nucleotide long oligonucleotide primers which are complimentary to both the strands of target DNA.
5. All four types of deoxyribonucleotides are required- dATP, dGTP, dCTP, dTTP .

All the above mentioned items are mix together to make a reaction mixture.

• Working mechanism of PCR

The process of PCR involves heating and cooling called thermal cycling which is carried out by machine 

called Thermocycler. 

There are three steps in one amplification cycle:- 

1. Denaturation 

2. Annealing or renaturation 

3. Extension 

1)Denaturation-

Firstly, the reaction mixture is heated at about 95C for one minute as a result of which the hydrogen bond between two DNA strands are breaks and two single strands of DNA are completely separated.

 

After denaturation the reaction mixture is slowly cooled down to 55- 66C temperature which is favorable for primers to bind the single stranded DNA strand by way of hydrogen bonding. This process is also called renaturation. 

3) Synthesis or extension or polymerisation:-

It is the final step of amplification cycle. IN the presence of Mg++ ions and dNTPs. (example - dATP, dGTP, dCTP, dTTP). 

Taq polymerase which is a thermostable bacteria initiates the synthesis of DNA at 3’ hydroxyl end of each primer and The primers are extended by joining the bases complementary to DNA strands. Thus, in the first cycle the target DNA is copied from the primer sites for various distances until the second cycle starts. 

After that second cycle of amplification is started for this the DNA strands are denatured which are original and newly synthesized long templates annealed with primers and subjected to DNA 

synthesis. 

 The no. of DNA strands becomes four times at the end of second cycle. In this way at the end of 32nd cycle of PCR, about million fold target DNA is synthesized. 

 After PCR has been completed the results are usually visualize using gel electrophoresis (A technique in which fragments of DNA are pulled through gel by a electric current and it separates DNA fragment according to size.

Properties of Immunoglobulin G - Notes for College students and all the points to be added in exams to get good marks

• Molecular weight of immunoglobulin G is 150,000.
• Serum Concentration of immunoglobulin G is→ 12 mg/ml .H-chain type of immunoglobulin G is gamma.
• Percent of immunoglobulin G in total immunoglobulins is - 80%
• longest half life of immunoglobulin G is 23 days.
• Immunoglobulin G Produce secondary response.
• Immunoglobulin G can activate Complement System.
• Immunoglobulin G is provide immunity to foetus.
• Immunoglobulin G is Bivalent antibody.
• Immunoglobulin G is only antibody to pass from placenta.