GMOs and Organic Produce
How organisms are genetically modified for specific traits & how this differs from organic.
Genetic Material
A Cell's Genome: DNA
DNA structure
Deoxyribonucleic acid (DNA) is the genetic material of all living organisms. Its double helix structure is composed of nucleotides. Each nucleotide has three parts: a nitrogenous base, deoxyribose sugar (5-carbons), and phosphate group. Phosphodiester bonds join the nucleotides together. The deoxyribose sugar and phosphate make up the backbone of the DNA. There are four different nitrogenous bases in DNA, divided into two groups: pyrimidines and purines. Adenine and guanine are purines and are composed of two carbon-nitrogen rings. The pyrimidines, which only contain one carbon-nitrogen ring, are cytosine and thymine. One purine and one pyrimidine are paired to form a base pair (A-T & G-C). The deoxyribose sugar and phosphate make up the backbone of the DNA, while base pairs join two nucleotide sequences to form the double helix structure as shown in the figure below.
An organism’s entire set of DNA is referred to as its genome. In Eukaryotic cells, a majority of the DNA is found in the membrane-bound nucleus. In prokaryotes, DNA is held in the central region of the cell, called the nucleoid, which has no membrane. The DNA is tightly bound and held in structures known as chromosomes, which is discussed below.
chromosomes & genes
Chromosomes are composed of DNA and allow genetic information to get passed on from parent to offspring. Eukaryotic organisms have multiple linear chromosomes, while prokaryotes have a singular circular chromosome. Each species is characterized by its number of chromosomes. For example, humans have 46 chromosomes in a typical body cell. Humans are diploid (2n), which indicates that chromosomes are present in matched sets, known as homologous pairs. Therefore, the 46 human chromosomes are organized into 23 homologous pairs.
The only exception to homologous chromosome pairing occurs in human gametic cells (sperm & eggs). These cells only contain one homologous chromosome from each pair. These cells, therefore, are considered haploid (1n). When a sperm and egg fuse, their genetic material combines, forming a diploid (2n) set of chromosomes. Therefore, in each homologous pair, one homologue comes from the father and the other comes from the mother. The X and Y chromosomes determine an individual’s biological sex: XX is female and XY is male. Because of this, these chromosomes are referred to as sex chromosomes. The remaining 44 chromosomes are called autosomes.
Small segments of DNA, present in chromosomes, are genes. They are the basic unit of heredity. Genes determine specific characteristics by coding for specific proteins. Corresponding genes are found within homologous chromosomes. For example, the gene found near the bottom of chromosome 15 affects eye color. Both homologous chromosomes contain the same genes in the same locations, but they may contain different versions of that gene. In reference to eye color, one chromosome may contain the gene corresponding to blue eyes, while the other homologue has the brown eye color gene. These alleles (variations of a gene) contribute to the natural variation within species. Sex chromosomes don’t follow this homologous chromosome uniformity. Other than a small amount of homology that is necessary to accurately produce gametes, the genes found on the X and Y chromosomes are different.
Genetically Modified Organisms
genetic engineering
Genetic engineering is the alteration of an organism’s genetic material using recombinant DNA technology to modify an organism’s DNA to achieve desirable traits. The organism that receives the recombinant DNA is considered a genetically modified organism (GMO). If the foreign DNA comes from a different species, the host organism is transgenic. Scientists have genetically modified bacteria, plants, and animals since the early 1970s for academic, medical, agricultural, and industrial purposes. In the United States, GMOs such as Roundup-ready soybeans and borer-resistant corn are part of many common processed foods. Importantly, federal agencies implement regulations for GMOs to ensure safety.
Identify
Scientists identify which trait they desire for a specific organism and find an organism that has that desired trait within its genes
Copy
After locating the desired gene, scientists copy the gene’s particular DNA sequence.
Insert
Then, scientists use tools to insert the gene into the DNA of the host organism.
Grow
The new organism is grown and tested for the desired trait as well as tested for safety.
transgenic plants
As mentioned earlier, DNA from a separate species can be inserted into a host. Manipulating the DNA of plants (i.e., creating GMOs) has helped to create desirable traits, such as disease resistance, herbicide and pesticide resistance, better nutritional value, and better shelf-life. Plants are the most important source of food for the human population. Farmers developed ways to select for plant varieties with desirable traits long before modern-day biotechnology practices were established. Think back to the previous lesson! Both natural and artificial selection influence what traits will be passed down to the next generation. We call plants that have received recombinant DNA from other species transgenic plants. Because they are not natural, government agencies closely monitor transgenic plants and other GMOs to ensure that they are fit for human consumption and do not endanger other plant and animal life. Because foreign genes can spread to other species in the environment, extensive testing is required to ensure ecological stability. Staples like corn, potatoes, and tomatoes were the first crop plants scientists genetically modified.
Organic Products
The United States Department of Agriculture (USDA) not only regulates GMOs but organic products as well. To be classified as “organic” organisms must be grown, cared for, and processed under a specific set of conditions. First of all, no organic products may be grown or handled using GMOs. Keep in mind that products stating “made with organic” are only required to contain 70% organic ingredients.
Meat
- Animals must be raised according to their natural behaviors
- Animals are fed 100% organic feed
- Animals are not administered antibiotics or hormones
Produce
- Plants are grown in soil that has had no prohibited substances applied for at least three years
- No synthetic fertilizers or pesticides are used on the produce
Processed
- Processed foods cannot contain artificial flavorings or colorings
- Each ingredient in the final product must be certified organic
