Given above is the schematic representation of lac operon of E.coli. Explain the functioning of this operon when lactose is provided in the growth medium of the bacteria.

OR

Using Punnett square show the F2 results of a dihybrid cross where the pure breed parents have contrasting traits with reference to seed shape and seed colour in Pisum Sativum. Give the phenotypic ratio.

The functioning of this operon when lactose is provided in the growth medium of the bacteria is as follows -

Lactose enters the cell with the help of lactose permease which is already present in a small amount in the beginning. Lactose then binds to the active repressor changing its conformation. This is when the repressor fails to bind to the operator region (o). So, now the RNA polymerase is able to bind to the promoter (p) region. Hence all the three enzymes (lactose permease (from y) , transacetylase (from a) and beta-galactosidase (from z) are secreted). Allolactose is the actual inducer and not lactose.

OR

According to Mendel's law of independent assortment, when two pairs of traits are combined in a hybrid, segregation of one pair of character is independent of the other pair of characters i.e. no intermediate traits are expressed.

The cross for the given situation can be drawn in the following way:

In the given case, 'Y' is the genotypic symbol for dominant yellow seed colour, symbol 'y' for recessive green seed colour, symbol 'R' for dominant round shape of seed and symbol 'r' for recessive wrinkled seed in garden pea.