Question

What is the genetic material of chromosomes? Explain what a gene is. Explain why a person has two genes for each protein or trait. (p. 482)

Short answer

Answer: People have two genes for each protein or trait because they are diploid organisms with two sets of chromosomes, one from each parent. Since each chromosome carries a set of genes, there are two alleles of each gene, one from the mother and one from the father, which together determine the expression of a particular trait or characteristic.

Step-by-step solution

Genetic material of chromosomes

The genetic material of chromosomes is deoxyribonucleic acid (DNA). DNA is a long molecule made up of nucleotides, which are the building blocks of DNA. Each nucleotide consists of a sugar molecule, a phosphate group, and one of four nitrogenous bases (adenine, thymine, guanine, or cytosine). DNA carries the genetic information needed for the development, functioning, and reproduction of living organisms.

Definition of a gene

A gene is a segment of DNA that contains the instructions for the synthesis of a particular protein or RNA (ribonucleic acid) molecule. These instructions are encoded by the specific sequence of nucleotides within the gene, which is transcribed and translated into the amino acid sequence of a protein or the structure of an RNA molecule. Genes regulate the production of proteins and other biomolecules, which in turn determine the traits and characteristics of an organism.

Two genes for each protein or trait

Each person has two genes for each protein or trait because humans are diploid organisms, meaning they have two sets of chromosomes, one from each parent. In humans, there are 23 pairs of chromosomes, totaling 46 chromosomes. For each pair, one chromosome comes from the mother (egg) and the other from the father (sperm). Since each chromosome contains a set of genes, this means that there are two versions (alleles) of each gene, one from each parent. These two alleles of a gene may be the same or different, and they work together to determine the expression of a particular trait or characteristic in the person.

Key concepts

Unveiling the Essence of DNA

Imagine the blueprint of life, an intricate code that tells a story of heredity and forms the essence of every living organism. This code is none other than DNA, or deoxyribonucleic acid, which is the genetic material nestled within the heart of each cell's chromosomes. DNA is essentially a long and winding molecule, composed of smaller units called nucleotides, each of which includes a sugar molecule, a phosphate group, and one of four nitrogenous bases: adenine (A), thymine (T), guanine (G), or cytosine (C).

These bases pair up in a specific manner—A with T, and C with G—to form the rungs of a spiraling ladder structure known as the double helix. The order of these bases dictates the genetic instructions or the genomic 'language' necessary for the development, functioning, and ability of organisms to reproduce. Furthermore, the DNA stored in chromosomes is replicated during cell division, ensuring that genetic information is faithfully transmitted from one generation to the next.

Understanding Genes

But what about genes? What role do they play within this genomic orchestra? A gene is fundamentally a distinct segment of DNA that serves as a set of instructions for building protein molecules, the workhorse compounds of life, or for creating molecules of RNA involved in protein synthesis and other essential functions. The sequence of nucleotides within a gene is like a sentence in the storybook of life, spelling out particular instructions that guide the construction of proteins.

These proteins go on to play a pivotal role in defining an organism's traits—ranging from eye color to enzyme activity. It is the unique combination and regulation of different genes, through processes like transcription and translation, that gives rise to the diverse forms and functions observed in living beings. Interestingly, a single gene can have multiple versions or 'alleles,' which can influence the variability of traits among individuals in a population, shaping not just individual uniqueness but also the tapestry of biodiversity.

Diploid Organisms and Genetic Diversity

In the realm of human genetics, the term 'diploid' refers to the possession of two complete sets of chromosomes, one inherited from each parent. This indicates that for virtually every gene, a person carries two copies, or alleles—one from their mother and another from their father. Humans, being diploid organisms, boast a total of 46 chromosomes, making up 23 pairs. This chromosomal partnership ensures that genetic material mixes during reproduction, fueling the incredible diversity that characterizes the human species.

During the process of sexual reproduction, sperm and egg cells, which are haploid (carry single sets of chromosomes), combine to produce a diploid zygote. This mingling of genetic material from two parents not only provides the basis for hereditary traits but also contributes to genetic variation among offspring. Coupled with the occurrence of random mutations, this variation is the driving force behind evolution and the survival proficiency of species throughout the ebbs and flows of environmental changes.