Q2 of 33 Page 10

What are genes?

The unit of heredity transmitted from one generation to next are called genes. Genes occur on the chromosome and they go wherever chromosomes go. Each chromosome has a number of genes. Each gene is present at a specific position on a chromosome called its locus. Gene is a segment of a DNA that encodes particular proteins which express in the form of some particular feature of the body.


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3

Correct the following statements if there is any mistake.

(a) The four nitrogenous bases in the DNA are Guanine, Thiamine, Adrenaline, and Cytosine.


(b) Genes are specific sequences of bases on a chromosome.


(c) A nucleotide is composed of a sulphate, a sugar (pentose) and a nitrogenous base.


(d) Nucleosome is group of cysteine molecules surrounded by DNA strands.


(e) If there are 46 chromosomes in a cell, there will be 23 chromatin fibers inside the nucleus during interphase.

 1

What are nucleosomes?

 1

Given below is a schematic diagram of a portion of DNA.


(a)How many strands are shown in the diagram?


(b) How many nucleotides have been shown in each strand?


(c) Name the parts numbered 1, 2, 3, 4 and 5 respectively.


(d) Name the DNA unit constituted by the parts 1, 2 and 3 collectively.

 2

The three sketches gave below (A, B and C) are intended to represent the replication of DNA. What should be their correct sequence starting with the first and ending with the last?