Variations in our genetic code

All humans have the same set of genes, and the sequence of our base pairs is remarkably similar. However, this doesn't mean that we all have exactly the same nucleotide sequence in our genome.

The passage of the genetic code from generation to generation via the sperm and ova of our ancestors requires replication of DNA, and while replication is remarkably precise, errors occasionally occur and produce changes in the base sequence. It is these changes that produce the variation that makes each of us genetically unique (except for identical twins), and they also drive evolution of species.

There may be a variation in the sequence of letters in the message, a deletion or insertion of individual letters into the code or the deletion or insertion of one or more whole words within the message. Even a deletion of the whole gene can occur.

Variations in the code can occur during our life for a variety of reasons including exposure to radiation or certain chemicals. However, ageing is one of the most common causes of genetic variation. Our cells need to be continually replaced: the cells (and their genetic make-up) are copied over and over again as time goes by. Sometimes mistakes occur in this copying process, and variations in the genes build up in our cells.

Notes to the texts:

passage – проходження; прохід, перехід

via – через, за допомогою

sperm – сперма

ova – яйцеклітини

ovum – яйцеклітина

ancestor – предок, прабатько

identical twins – однояйцеві близнюки

drive – рухати

deletion – викреслювання; витирання

insertion – вставляння; включення

exposure – виставляння, оголення

VIII. Answer the following questions to check how carefully you have read the text:

1. What kind of genes do all humans have?

2. Is the sequence of our base pairs remarkably similar?

3. Do we have exactly the same nucleotide sequence in our genome?

4. What does the passage of the genetic code from generation to generation require?

5. What do replication errors occasionally produce?

6. What makes each of us genetically unique?

7. What kind of genetic variations may occur?

8. What are the reasons for the variations in the genetic code?

9. What is one of the most common causes of genetic variation?

10. What do our cells need?

IX. Complete the following to make suitable sentences according to the text:

1. All humans have the same …

2. While replication is remarkably precise, …

3. Changes in the base sequence drive …

4. Variations in the code can occur during our life …

5. … need to be continually replaced.

6. However, ageing …

X. Put the words in the right order to make a sentence:

1. hereditary, by which, into, the set of rules, The genetic code, information, is, is, translated, proteins.

2. of DNA, their genes, living organisms, encode, in long strands, The vast, majority of.

3. are, genes, operons, Many, prokaryotic, into, organized.

4. helix, very, DNA, A chromosome, thousands of genes, consists, which, are, of, a single, long, on, encoded.

5. chromosomes, 1, There are, sex, pairs, 22, of, autosomes, pair, of, and.

6. an XY chromosome, an XX chromosome, Females, have, have, men, while.

7. the human, up, All the DNA, genome, the cell, in, makes.

Дата добавления: 2015-10-26