Question 1

As much as biologists talk about genes, the term is devilishly difficult to define. The word gene was coined in 1909 to denote an abstract “unit of heredity” .

Accepted Answer

by which a trait passes from parent to offspring. No one had the foggiest idea at the time, though, of what chemical or physical form a gene had—of what a gene was

Question 2

Following discovery of the double helix, molecular biologists worked out the genetic code contained in the four bases of DNA and considered a gene to be a segment of the DNA that carries the code for a particular protein.

Accepted Answer

Now, however, we know that the human body has millions of different proteins but only 22,300 protein-coding genes; obviously there isn’t a separate gene for every protein.

Question 3

In addition, we know now that several human genes produce only ncRNA molecules that never go on to direct the synthesis of a protein; RNA is their final product. Other recent discoveries have complicated our concept of the gene still more—

Accepted Answer

genes overlapping each other, so some segments of DNA belong to two different genes; short genes embedded within longer ones; multiple related proteins encoded by a single gene; and other unexpected arrangements.

Question 4

As molecular biologists have learned more and more about DNA,

Accepted Answer

the definition of the gene has become more and more frayed around the edges.

Question 5

define gene as an information-containing segment of DNA that codes for the production of a molecule of RNA,

Accepted Answer

which in most cases goes on to play a role in the synthesis of one or more proteins. The amino acid sequence of a protein is determined by a nucleotide sequence in the DNA.

Question 6

The 46 human chromosomes come in two sets of 23, one set from each parent. Some of these are gene-rich, such as chromosomes 17, 19, and 22, whereas others are gene-poor, such as 4, 8, 13, 18, 21, and the Y chromosome (see fig. 4.16).

Accepted Answer

All the DNA, both coding and noncoding, in one 23-chromosome set is called the genome. The total genome consists of about 3.1 billion nucleotide pairs. Individual genes average about 3,000 nucleotides long, but range up to 2.4 million.

Question 7

Most genes are identical in every human being. All humans, worldwide, are at least 99.99% genetically identical, but even the 0.01% variation means that we can differ from one another in more than 3 million base pairs.

Accepted Answer

Various combinations of these single-nucleotide polymorphisms account for all human genetic variation.

Question 8

Genomics is a relatively young science concerned with the comprehensive study of the genome and how its genes and noncoding DNA affect the structure and function of the organism.

Accepted Answer

Among the other fruits of this research, we now know the chromosomal locations of more than 1,400 disease-producing mutations. This information has opened the door to a branch of medical diagnosis and therapy called genomic medicine

Question 9

Genomic medicine is the application of our knowledge of the genome to the prediction, diagnosis, and treatment of disease.

Accepted Answer

It is relevant to disorders as diverse as cancer, Alzheimer disease, schizophrenia, obesity, and even a person’s susceptibility to nonhereditary diseases such as AIDS and tuberculosis.

Question 10

Genomic technology has advanced to the point that for less than $1,000, one can have one’s entire genome scanned for markers of disease risk. Because knowing one’s genome could dramatically change clinical care.

Accepted Answer

It may allow clinicians to forecast a person’s risk of disease and to predict its course; mutations in a single gene can affect the severity of such diseases as hemophilia, muscular dystrophy, cancer, and cystic fibrosis.

Question 11

Genomics should also allow for earlier detection of diseases and for earlier, more effective clinical intervention. Drugs that are safe for most people can have serious side effects in others, owing to genetic variations in drug metabolism.

Accepted Answer

Genomics has begun providing a basis for choosing the safest or most effective drugs and for adjusting dosages for different patients on the basis of their genetic makeup.

Question 12

Knowing the sites of disease-producing mutations expands the potential for gene-substitution therapy.

Accepted Answer

This is a procedure in which cells are removed from a patient with a genetic disorder, supplied with a normal gene in place of the defective one, and reintroduced to the body.

Question 13

The hope is that these genetically modified cells will proliferate and provide patients with gene products they were lacking—perhaps insulin for a patient with diabetes or a blood-clotting factor for a patient with hemophilia.

Accepted Answer

Researchers are currently exploring a new gene-editing technology called CRISPR-Cas9 that enables one to locate a specific gene in the DNA and remove or replace it.

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