Adaptations

Water lilies, a kind of adaptations

The results of natural selection in which succeeding generations of organisms become better able to live in their environments are called adaptations. Many of the features that are most interesting and beautiful in biology are adaptations. Specialized structures, physiological processes, and behaviors are all adaptations when they allow organisms to cope successfully with the special features of their environments.

Adaptations ensure that individuals in populations will reproduce and leave well-adapted offspring, thus ensuring the survival of the species. Adaptations arise through mutations—inheritable changes in an organism’s genetic material.

These rare events are usually harmful, but occasionally they give specific survival advantages to the mutated organism and its offspring. When certain individuals in a population possess advantageous mutations, they are better able to cope with their specific environmental conditions and, as a result, will contribute more offspring to future generations than those individuals that lack the mutation.

Adaptive Radiation

Galapagos cacti

In adaptive radiation, numerous species evolve from a common ancestor introduced into an environment with diverse ecological niches. The progeny evolve genetically into customized variations of themselves, each adapting to survive in a particular niche.

In 1898 Henry F. Osborn identified and developed the evolutionary phenomenon known as adaptive radiation, whereby different forms of a species evolve, quickly in evolutionary terms, from a common ancestor.

According to the principles of natural selection, organisms that are the best adapted (most fit) to compete will live to reproduce and pass their successful traits on to their offspring. The process of adaptive radiation illustrates one way in which natural selection can operate when members of one population of a species are cut off or migrate to a different environment that is isolated from the first.

Bacterial Genetics

Bacterial Genetics

Bacterial genetics is the study of the genetic material of bacterial DNA, which can provide valuable insights into the process of mutation because of bacteria’s rapid rate of reproduction.

Plants were the original candidates for genetic studies, which began in the late 1800’s. Studies with animals soon followed; bacteria did not become candidates for such study until the mid-1940’s, when adequate technology for handling bacteria developed. Bacteria have become extremely useful organisms for genetic studies since the early 1950’s.

Two major features of bacteria make them desirable subjects. First, bacterial cells typically divide every twenty minutes. Their rapid rate of reproduction allows a very large number of bacteria to be produced in a short time. This, in turn, provides the researcher with more opportunity to detect the "rare genetic events" of mutation or recombination.

Bacteriophages

Bacteriophages

Viruses that attack bacterial cells are known as bacteriophages. Many results gained from studying bacteriophages have universal implications.

For example, the physical properties of DNA and RNA are remarkably identical in all organisms, and these are perhaps easiest to study in bacteriophage systems.

Bacteriophages, or phages for short, are viruses that parasitize bacteria. Viruses are an extra ordinarily diverse group of ultramicroscopic particles, distinct from all other organisms because of their noncellular organization.

Biotechnology

Biotechnology

Biotechnology is the use of living organisms, or substances obtained from those organisms, to produce processes or products of value to humanity, such as foods, high-yield crops, and medicines.

Modern biotechnological advances have provided the ability to tap into a natural resource, the world gene pool, with such great potential that its full magnitude is only beginning to be appreciated.

Theoretically, it should be possible to transfer one or more genes from any organism in the world into any other organism. Because genes ultimately control how any organism functions, gene transfer can have a dramatic impact on agricultural resources and human health in the future.

Chloroplast DNA

Chloroplast DNA

Plants are unique among higher organisms in that they meet their energy needs through photosynthesis. The specific location for photosynthesis in plant cells is the chloroplast, which also contains a single, circular chromosome composed of DNA. Chloroplast DNA contains many of the genes necessary for proper chloroplast functioning.

A better understanding of the genes in chloroplast deoxyribonucleic acid (cpDNA) has improved the understanding of photosynthesis, and analysis of the deoxyribonucleic acid (DNA) sequence of these genes has been useful in studying the evolutionary history of plants.

Discovery of Chloroplast Genes

The work of nineteenth century Austrian botanist Gregor Mendel showed that the inheritance of genetic traits follows a predictable pattern and that the traits of offspring are determined by the traits of the parents.

Chromatin

Chromatin

Chromatin is an inclusive term referring to DNA and the proteins that bind to it, located in the nuclei of eukaryotic cells. The huge quantity of DNA present in each cell must be organized and highly condensed in order to fit into the discrete units of genetic material known as chromosomes. Gene expression can be regulated by the nature and extent of this DNA packaging in the chromosome, and errors in the packaging process can lead to genetic disease.

Scientists have known for many years that the hereditary information within plants and other organisms is encrypted in molecules of deoxyribonucleic acid (DNA) that are themselves organized into discrete hereditary units called genes and that these genes are organized into larger subcellular structures called chromosomes.

James Watson and Francis Crick elucidated the basic chemical structure of the DNA molecule in 1952, and much has been learned since that time concerning its replication and expression.

Chromosomes

Chromosomes

Chromosomes contain the genetic information of cells. Replication of chromosomes assures that genetic information is correctly maintained as cells divide.

The genome of an organism is the sum total of all the genetic information of that organism. In eukaryotic cells, this information is contained in the cell’s nucleus and organelles, such as mitochondria and plastids. In prokaryotic organisms (bacteria and archaea), which have no nucleus, the genomic information resides in a region of the cell called the nucleoid.

A chromosome is a discrete unit of the genome that carries many genes, or sets of instructions for inherited traits. Genes, the blueprints of cells, are specific sequences of deoxyribonucleic acid (DNA) that code for messenger ribonucleic acids (monas), which in turn direct the synthesis of proteins.

Clines

Clines

A cline is one form of geographic variation in which characteristics of a species change gradually through the species’ geographic range.

Many plant and animal species have populations that differ in terms of their morphological, physiological, and biochemical characteristics. A species is generally defined as a group of organisms that have the potential to interbreed and produce fertile offspring.

A population is defined as a group of organisms which are actively interbreeding. The following example will clarify the relationship between species and populations and simultaneously introduce geographic variation.

Cloning of Plants

Cloning of Plants

Plant cloning is the production of a cell, cell component, or plant that is genetically identical to the unit or individual from which it was derived.

The term“clone” is derived from the Greek word klon, meaning a slip or twig. Hence, it is an appropriate choice. Plants have been “cloned” from stem cuttings or whole-plant divisions for many centuries, perhaps dating back as far as the beginnings of agriculture.

Historical Background

In 1838 German scientists Matthias Schleiden and Theodor Schwann presented their cell theory, which states, in part, that all life is composed of cells and that all cells arise from preexisting cells.

DNA in Plants

DNA in Plants

DNA is the hereditary or genetic material, present in all cells, that carries information for the structure and function of living things.

In the plant kingdom, DNA, or deoxyribonucleic acid, is contained within the membrane-bound cell structures of the nucleus, mitochondria, and chloroplasts. DNA has several properties that are unique among chemical molecules.

Recombinant DNA Technology

Recombinant DNA technology result

Recombinant DNA technology makes use of science’s understanding of the molecular structure of DNA, the nucleic acid that encodes genetic information, to alter DNA in order to manipulate genetic traits. Such technology has immense implications for agriculture, horticulture, and the generation of medicinal compounds from plants.

Recombinant DNA technology has been essential for understanding DNA sequences. Because of their large, complex genomes, it was difficult to study one gene in eukaryotes, but recombinant DNA technology has allowed the isolation and amplification of specific DNA fragments facilitating the molecular analysis of genes. In addition, the tools of recombinant DNA technology have been used to create genetically modified plants.

Such modifications include the introduction of resistance to insects, herbicides, viruses, and bacterial and fungal diseases into plants. Plants have also been made to produce antibodies so that plants can serve as edible vaccines.

DNA replication

DNA replication

DNA, deoxyribonucleic acid, is the hereditary material of most living creatures. It carries genetic information that determines all types of plant lives. DNA replication is a process by which a single DNA molecule is copied, resulting in two identical molecules prior to the cell division. The accuracy and precision in DNA replication has ensured the continuity of life from generation to generation.

Following James Watson and Francis Crick’s landmark proposal for the structure of the deoxyribonucleic acid (DNA) molecule in 1953, many scientists turned their attention to how this molecule is replicated.

Extranuclear Inheritance

Extranuclear inheritance is a non-Mendelian form of heredity that involves genetic information located in cytoplasmic organelles, such as mitochondria and chloroplasts, rather than on the chromosomes found in the cell nucleus.

Extranuclear genes, also known as cytoplasmic genes, are located in mitochondria and chloroplasts of a cell rather than in the cell’s nucleus on the chromosomes. Both egg and sperm contribute equally to the inheritance of nuclear genes, but extranuclear genes are more likely to be transmitted through the maternal line because the egg is rich in the cytoplasmic organelles where these genes are located, whereas the sperm contributes only its nucleus to the fertilized egg.

Therefore, extranuclear genes do not follow genetic pioneer Gregor Mendel’s statistical laws of segregation and recombination. Cytoplasmic genes are of interest in understanding evolution, genetic diseases, and the relationship between genetics and embryology.

Gene Flow

Gene flow represents a recurrent exchange of genes between populations. This exchange results when immigrants from one population interbreed with members of another.

Charles Darwin published On the Origin of Species by Means of Natural Selection in 1859. Since then, scientists have modified and added new concepts to the theory of evolution by natural selection. One of those concepts, which was only dimly understood in Darwin’s lifetime, is the importance of genetics in evolution, especially the concepts of migration and gene flow.

Genes

Genes are elements within the cells of a living organism that control the transmission of hereditary characteristics by specifying the structure of a particular protein or by controlling the function of other genetic material. Within any species, the exchange of genes via reproduction is constant among its members, ensuring genetic similarity.

Gene Regulation

Genetic regulation is the manner in which a cell carries out transcription of its DNA (by copying it to messenger RNA) and the production of corresponding protein, called translation.

When a gene is expressed, one strand of that gene’s double helical deoxyribonucleic acid (DNA) is copied, in the process of transcription, by an enzyme called RNA(ribonucleic acid) polymerase to make a messenger RNA (mRNA).

The mRNA then associates with a ribosome (formed by specific ribosomal RNAs and proteins), where the nucleic acid base sequence is read, to produce the corresponding protein in a process called translation.

Genetic Code

The genetic code defines each amino acid in a protein, or polypeptide, in terms of a specific sequence of three nucleotide called codons, in the DNA. The genetic code is therefore the key to converting the information contained in genes int proteins.

The genetic code defines each amino acid in a protein, or polypeptide, in terms of a specific sequence of three nucleotides, called codons, in the deoxyribonucleic acid (DNA). Therefore, the genetic code is called a triplet code.

The four different nucleotides in DNA can form sixty-four different triplet codons. Because there are only twenty amino acids found in proteins, some amino acids are encoded by more than one codon. Therefore, the genetic code is said to be redundant, or degenerate.

Genetic Drift

Genetic drift refers to random changes in the genetic composition of a population. It is one of the evolutionary forces that cause biological evolution, the others being selection, mutation, and migration, or gene flow.

Drift occurs because the genetic variants, or alleles, present in a population are a random sample of the alleles that adults in the previous generation would have been predicted to pass on, where predictions are based on expected migration rates, expected mutation rates, and the direct effects of alleles on fitness.

If this sample is small, then the genetic composition of the offspring population may deviate substantially from expectation, just by chance. This deviation is called genetic drift.

Genetic Equilibrium: Linkage

Linkage

Genetic equilibriumis the tendency for genes located close together on the same chromosome to be inherited together. The farther apart the genes, the less likely it is that they will be passed along together.

The genetic complement of any organismis contained on one or more types of chromosomes. Whether there are only a few chromosomes or many (such as in a diploid organism), each type occurs as a set of two, called homologs.

Each gene at a particular locus, or site, along the chromosome occurs twice in the same cell (except for some loci which only occur on one of the two sex chromosomes), one copy of each homolog. The particular information at each locus may be different because genes can exist in several forms.

Genetically Modified Bacteria

Bacteria may be genetically modified through the introduction of recombinant DNA molecules into their cells. Such bacteria may be used to produce human insulin or introduce disease-resistant genes into plants, as well as numerous other applications.

The ability to genetically engineer bacteria is the outcome of several independent discoveries. In 1944 Oswald Avery and his coworkers demonstrated gene transfer among bacteria using purified DNA (deoxyribonucleic acid), a process called transformation.

In the 1960’s the discovery of restriction enzymes permitted the creation of hybrid molecules of DNA. Such enzymes cut DNA molecules at specific sites, allowing fragments from different sources to be joined within the same piece of genetic machinery.