(a) Write what DNA replication refers to.

(b) State the properties of DNA replication model.

(c) List any three enzymes involved in the process along with their functions.

OR

Inheritance patterns of flower colour in garden pea plant and snap dragon differ. Why is the difference observed? Explain the difference with the help of crosses in their inheritance patterns.

(a) The process in which the two strands of DNA separate and act as template for the synthesis of new complementary strands is called DNA replication.

(b)

Properties of Replication model –

• The DNA helix opens a small opening where the replication occurs. This opening is called replication fork which has two DNA strands called template strands.

• One of the template strand has polarity 3’ → 5’. Replication is continuous on this strand while discontinuous on the other strand with polarity 5’ → 3’.

• After the completion of DNA replication, two DNA molecules will be formed and each molecule will contain one template strand and one complementary strand. This is called semiconservative DNA replication model.

• DNA is always polymerized only in 5’ → 3’ direction. Therefore, the process is unidirectional.

(c) The enzymes involved in the process are –

• DNA ligase – this enzyme joins the okazaki fragments to form a single strand of DNA.

• Gyrase – it relaxes the supercoiling of the template strands.

• Helicase – this enzyme breaks the hydrogen bonds.

OR

In garden pea, the inheritance patterns of flower colour follow the law of dominance.

The law of dominance states that in a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. The expressed allele is called dominant allele while the other one is recessive. The allele responsible for purple/violet flowers is dominant over the allele responsible for the white.

In snapdragon, the inheritance pattern of flower colours follows the law of incomplete dominance. According to the law of incomplete dominance, the dominant allele is not completely dominant over the recessive allele due to which the progeny obtained by crossing homozygous red flower plant and homozygous white flower plant is heterozygous pink flower plant (i.e neither red nor white).