Introduction to Genetics

Gregor Mendel, an Austrian scientist and monk who lived during the 1800s, is considered the “father of genetics.” His pioneering research work paved the way for understanding how traits are passed down from parents to offspring. 

Gregor Mendel lived in a monastery in what is now known as the Czech Republic. Moving to a monastery was the only way Mendel could escape the poverty of his former life and pursue his studies.

Mendel studied hybridization, breeding 2 varieties of a species to create offspring showing characteristics of both varieties. 

Previous scientists noted that hybrid offspring would sometimes revert back to one of the original parent species and the abbot of Mendel’s monastery wanted to know why.

Mendel used pea plants to conduct his hybridization experiments as there were quite a few different varieties available for his research. In addition to being easy to grow and easy to cross-pollinate, the plants grew quickly.

Mendel followed 7 distinct traits including plant height, flower color, and seed color. He grew over 30,000 pea plants in 15 years, giving names to the plants and assigning alphabet letters to the pea plant generations. 

Mendel’s major discovery was that traits (genes) come in pairs. He noticed that some traits would always “win out” over others. He called these traits dominant. Although he had only studied pea plants, Mendel theorized that all living things had such traits.

Heredity refers to the passing down of genetic information from parent to offspring, a process that applies to all living things. This information gets passed down in the form of genes, tiny pieces of information located inside DNA. 

DNA, which stands for deoxyribonucleic acid, is found tightly coiled within chromosomes. The length of DNA strands varies; the average length of a human strand of DNA measures 5–6 feet long. These strands contain all the information needed to create a living organism.

Genes are tiny pieces of information in DNA, with the full collection of an organism’s genes called a genome. Each gene provides instructions for traits such as eye color, hair color, height, and even whether you sneeze after suddenly being exposed to bright light!

Half of the genetic information for each organism is provided by the biological mother, and half is provided by the biological father. Each offspring receives 2 copies of every gene, 1 from each parent, with the copy from each parent being random.

Humans have learned that by consistently selecting desirable parental traits, a species can be bred to suit our purposes. Domesticated animals and crops are bred to produce more and larger fruit, run faster, or produce stronger individuals (as well as thousands of more traits).

The Human Genome Project was a multinational scientific effort to understand what each of the 3 billion base pairs does within human DNA. Begun in 1990, the project was declared completed in 2003. 

Scientists hoped the project would have impacts in the areas of life sciences, medicine, and biotechnology.

A chromosome is a tightly wound bundle of DNA and proteins located inside the nucleus of every cell. The nucleus of every human cell contains 46 chromosomes, organized into 23 coiled pairs. Plants and animals have different numbers of chromosomes.

Two strands of DNA join together in the shape of a double helix that looks like a spiraling ladder. The “rungs” are made up of pairs of bases: adenine (A), cytosine (C), guanine (G), and thymine (T). 

Many traits displayed by living things involve more than just a single gene found in that organism. For example, human height, or how tall a person will grow, is influenced by at least 400 gene regions. 

The Human Genome Project has already discovered 1,800 disease–causing genes. Due to the project, more than 2,000 genetic tests for human diseases now exist. Researchers are working on similar genomic studies in order to identify the causes of rare diseases.

 Thanks to the Human Genome Project, over 350 biotechnology projects that may benefit human health are now in clinical trials. 

Evolution is the slow changing of a species over a very long time. These changes happen over several generations and often occur due to long–term environmental stressors. 

The prevalence of traits for a species can change over time and natural genetic mutations can change a species entirely.

Sometimes DNA doesn’t replicate perfectly, known as a mutation. In this fictional pride of dark lions, a natural mutation has caused a lion to be born with light–colored fur. When this lion becomes a parent, it will pass the trait onto its offspring.

It turns out that the light–colored fur makes the lion blend into the grass more than dark–colored fur. This means the light–colored lions capture more prey and begin to breed more. Over many generations, light–colored lions are now more common than dark–colored lions.

Evolutionary trees are a visual representation that describes the gradual changes to a species over time. They help illustrate common ancestors of species. Recent trees reflect the results of genetic testing to determine the relationships between species.

A common ancestor is an animal from which 2 or more species diverged. This divergence could occur for many different reasons, including environmental stressors that may exact on one population but don’t exist in another.

Mutations occur when DNA fails to replicate exactly during cell division. Two types of genetic mutations exist, and mutations can vary in size from a single base pair to a large part of a chromosome that contains several genes.

Hereditary mutations are passed on from parent to offspring. They occur within either the egg or sperm of the parent organism. In these cases, the mutation is then present in every cell of the offspring’s body. 

Somatic, or acquired, mutations occur during the organism's lifetime. DNA may mutate after exposure to UV light or exposure to certain chemicals. Present only in certain cells, these types of mutations can’t be passed to offspring.

Some types of mutations will mean the individual is less likely to breed or survive to adulthood. A species that relies on camouflage to hide from predators won’t benefit from a mutation that causes the individual to stand out. 

Mutations that occur in more than 1% of a species population are called polymorphisms. Examples of human polymorphisms include eye color, hair color, and even blood type. Natural selection operates on this concept of genetic differences.

Genetic engineering is the deliberate manipulation of a species genome by humans. Humans have been practicing genetic engineering for thousands of years, carefully selecting desirable traits within domesticated animals and crops to breed. 

Modern genetic engineering can bring changes much faster and more accurately.

In 2003, researchers from many countries completed mapping the entire human genome. Understanding what each gene sequence does within the human body could mean that in the future, doctors can replace defective genes known to cause a wide range of genetic disorders.

The acronym GMO stands for Genetically Modified Organism. GMOs (primarily plants) have been changed at a genetic level to produce higher yield or have a natural resistance to pests and diseases. 

In most cases, they are modified with DNA from other organisms: bacterium, plant, virus, or animal. 

Scientists have spliced DNA from bacteria into plants in the mustard family to create a biodegradable plastic. This plant–based plastic that they created comes from totally renewable resources, and it will completely break down over time.