Mendelian Experiment

1. Monohybrid cross:

   Let the genotypes for tall be TT and for dwarf tt.

   First, the parent plants are cross pollinated to provide first filial generation (F1) and then F1 plants self-pollinated to give second filial generation (F2)

   In first filial generation all the plants are tall (i.e. only dominant character is seen, but all plants are hybrid) then in second filial generation there are 3 tall and one short plant (Only phenotypically but genotypically the plant is one tall two-hybrid and one dwarf).

   Genotypic ratio 1:2:1 (Dominant: Hybrid: Recessive) Phenotypic ratio 3:1 (Dominant: Recessive). Same goes for any other characters.

   

   

2. Dihybrid Cross:

   Let the two characters be shape of seed and color of seed and genotype be RRYY for pure round and yellow and rryy for pure wrinkled and green. Then these parent plants were first cross-pollinated to give F1 and then F1 were self-pollinated to give F2 generations. Ratio for the cross for second filial generation will be:

   Round and yellow = 9 Round and green = 3 Wrinkled and yellow =3 Wrinkled and green = 1

   

   

Mendelian Law:

On the basis of his experiments, Mendel came up with three conclusions on how characters behave when transmitted from generation to generation.

1. Law of Dominance: when a cross is made in between two pure contrasting characters in F1 generation one character is expressed while another one is hidden. Such expressed character is called dominant character and the masked character is called recessive character.
2. Law of purity of gametes: Though the genes, which control recessive character, are hidden in the hybrid organism it is present in the separate location of the chromosome, which later reappear while gametes are formed. This is also called the law of segregation as the heterozygous pair will separate during gamete formation.
3. Law of independent assortment: When two pairs of independent unit characters are brought together in the hybrid plant but at the time of gamete formation they assort or segregate randomly.

Variation:

Variation may be defined as morphological or a physiological change in an organism due to either genetic or physical reason.

Types of variation

1. Blastogenic variation: The variation that is initiated at the time of formation of zygote (better to say at the formation of gamete i.e. diplotene of meiosis I is called blastogenic variation.
2. Somatogenic variation: The variations, which are obtained at the lifetime of an individual because of environmental effect, is called somatogenic variation.

Variation in Maize

Difference between RNA and DNA

RNADNA