Read the given passage and answer the following questions:
In the preceding sections you have learnt that it is the sequence of bases in DNA that determines the genetic information of a given organism. In other words, genetic make-up of an organism or an individual lies in the DNA sequences. If two individuals differ, then their DNA sequences should also be different, at least at some places. These assumptions led to the quest of finding out the complete DNA sequence of human genome. With the establishment of genetic engineering techniques where it was possible to isolate and clone any piece of DNA and availability of simple and fast techniques for determining DNA sequences, a very ambitious project of sequencing human genome was launched in the year 1990. Some of the important goals of HGP were as follows: (i) Identify all the approximately 20,000-25,000 genes in human DNA; (ii) Determine the sequences of the 3 billion chemical base pairs that make up human DNA; (iiii) Store this information in databases; (iv) Improve tools for data analysis; (v) Transfer related technologies to other sectors, such as industries; (vi) Address the ethical, legal, and social issues (ELSI) that may arise from the project. The Human Genome Project was a 13-year project coordinated by the U.S. Department of Energy and the National Institute of Health. During the early years of the HGP, the Wellcome Trust (U.K.) became a major partner; additional contributions came from Japan, France, Germany, China and others. The project was completed in 2003.
Consider the following statements about the salient features of the human genome:
A. Repeated sequences make up very large portion of the human genome.
B. Repetitive sequences are stretches of RNA sequences that are repeated many times.
C. Repetitive sequences shed light on chromosome structure, dynamics and evolution.
D. Chromosome 1 has the fewest genes and the Y chromosome has the most genes.
E. The largest known human gene is dystrophin.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A, C and E only
A. Repeated sequences make up very large portion of the human genome. — True. Less than 2 per cent of the genome codes for proteins. A very large part is made of repeated sequences.
B. Repetitive sequences are stretches of RNA sequences that are repeated many times. — False. The genome is DNA, so its repetitive sequences are stretches of DNA, not RNA. They may be repeated hundreds to thousands of times.
C. Repetitive sequences shed light on chromosome structure, dynamics and evolution. — True. These sequences are thought to have no direct coding function, but they help us understand how chromosomes are built and how they evolved.
D. Chromosome 1 has the fewest genes and the Y chromosome has the most genes. — False. The two are swapped. Chromosome 1 has the most genes (2968) and the Y chromosome has the fewest (231).
E. The largest known human gene is dystrophin. — True. An average gene has about 3000 bases, but dystrophin has 2.4 million bases, the largest known.
NCERT Extract:
Salient Features of Human Genome – “… (ii) The average gene consists of 3000 bases, but sizes vary greatly, with the largest known human gene being dystrophin at 2.4 million bases. … (vi) Repeated sequences make up very large portion of the human genome. (vii) Repetitive sequences are stretches of DNA sequences that are repeated many times, sometimes hundred to thousand times. They are thought to have no direct coding functions, but they shed light on chromosome structure, dynamics and evolution. (viii) Chromosome 1 has most genes (2968), and the Y has the fewest (231).”