Question

1. Why did Gregor Mendel succeed in his work about understanding inheritance?

2. List and describe the function of the 4 enzymes involved in DNA replication.

3. List and describe 3 variations to Mendelian genetics.

4. List the steps of cell-cycle including the steps of Mitosis

Answer 1

1)Gregor Mendel succeed in understanding inheritance because he selected pea plant which is easily cultivable and has distinct characteristics.It can undergo self fertilisation. It also has a short life span and since he was a mathematician so he recorded his data for various generations.

2)The four enzymes involved in DNA replication are DNA polymerase which incorporates nucleotides to the strand in 5-3 direction forming leading strand and the lagging strand.The gyrase which releases the torsion strain and releives from positive supercoiling and initiate negative supercoiling.DNA ligase which catalyses the formation of phosphodiester bond between 3' OH and 5' phosphate.in the lagging strand.There is binding of SSB protiens to prevent the reannealing of the separated strands.The two DNA strands are separated by DNA helicase.

3)The variation to Mendel Genetics are incomplete dominance in which the offspring shows intermediate phenotype in which dominant trait does not masks the recessive trait completely.Eg flower colour on Snapdragon plant.

There is variation in which both the trait are eually expressed called as codominance.AB Blood grouping in humans.These differs from the Complete dominance law of Mendel.

Linkage is the exception to law of independent assortment. In which the inheritance of genes on the same chromosome are inherited together.

4)The cell cycle consists of G1 phase in which the proteins are synthesised which are required for the replication of DNA in the S phase.RNA is also synthesised during this phase.The cell at the end of the G1 phase have a checkpoint for the cell division or not.The cell which do not undergo cell division enter Go phase.

In the S phase DNA in the cell is doubled.

In the G2 phase there is synthesis of more RNA and proteins occur.The cell at the end of G2 interact with MPF(mitosis promoting factor)

The M phase or the mitotic phase is in which the cell divides into two daughter cells.

Prophase-At the end of the prophase the nuclear membrane is disrupted.There is condensation of chromatin material into chromosome.There is formation of spindle apparatus.

Metaphase-Spindle fibres attach to the kinetochore of the chromosome and relocate them to the center of the cell.In the metaphase the chromosome are arranged at the equatorial plate.At this stage morphology of the chromosome is best studied.

Anaphase-The sister chromatids migrate toward opposite poles and the centromere divides.This is called as disjunction of the chromosome

Telophase-It is marked by the appearance of the nuclear membrane and nucleolus.The spindle fibre disappears