Categories of Genetic Study

The study of genetics expanded greatly and quickly from that moment on. The first gene was sequenced in 1972 and both Richard Roberts and Phillip Sharp showed that genes could themselves be split in 1977. This furthered the concept that one gene could make several types of proteins. Genomes began to be sequenced and it was understood that certain genes could overlap with other genes.

The genomics era of genetics started in 1972 when the first gene was sequenced and continues today. Gene mapping was identified in 1980, which was also when the first US patent was awarded for gene cloning. The first genetically engineered insulin was approved in 1982 and the practice of polymerase chain reaction was invented in 1983, which is now used for DNA amplification in the diagnosis of infectious diseases.

In 1985, DNA fingerprinting techniques were created using chemical probes to examine DNA between different humans. By 1989, the CFTR gene that led to cystic fibrosis was first sequenced. Soon afterward, it became possible to use amniocentesis to identify hemophilia, cystic fibrosis, and other diseases in utero. The first breast cancer gene, called BRCA1 was discovered in 1994, followed closely by the identification of the second breast cancer gene, called BRCA2. The first cloned sheep was born in 1997. The Human Genome Project to sequence human DNA was completed in 2003.

CATEGORIES OF GENETIC STUDY

We have touched briefly already on the three major branches of genetics, which are classical genetics, molecular genetics, and population genetics. There are several areas of genetic study that are considered minor branches, such as behavioral genetics, developmental genetics, genetic engineering, genomics, human and medical genetics, microbial genetics, and psychiatric genetics. Let’s look at the three major branches studied today.

In classical genetics, research is based on the visible results of sexual reproduction. It dates back from the time of Gregor Mendel but has been expanded so it is understood now at a molecular level. At its heart is the concept of a gene being the basic unit of genetic transmission and on the idea that organisms are diploid, meaning they have two alleles of which one comes from the mother and one comes from the father.

Genetic linkage was identified through classical genetic study, showing that some genes do not separate independently at the time of meiosis in the creation of a gamete or sex cell, largely because the genes exist too close together on a chromosome. In classical genetic study, things like genes, heredity, and genetic variation are studied. Heredity is the ability of characteristics to be passed from parents to offspring. Genetic variation comes from the idea that related individuals are not identical to one another and the idea that traits are passed on through genes is part of this area of genetics as well.

Each sex cell, defined as sperm or an egg cell, has just one allele or copy of a chromosome or chromosomes so these cannot themselves make an organism. When these unite, however, they form a diploid gamete that has two alleles per chromosome. DNA in eukaryotes is defined as being linear so that each line of DNA together is called a chromosome. As mentioned, the genotype is the arrangement of genes that lead to a specific trait, while the phenotype is the physical expression of the genotype or what the organism looks like. Sometimes the term genotype is called its genetic makeup. Some alleles are dominant over others and are preferentially expressed, while others are recessive so they are not seen if the organism also has a dominant allele.

Molecular genetics, on the other hand, is a field of genetics that came after classical genetics. With molecular genetics, there are several interrelated fields of study connected to it, such as cell biology, inheritance, biochemistry, biotechnology, and molecular biology.

This branch of genetics was probably started in 1952, when the structure of DNA was first identified. It was expanded further when researchers used restriction endonucleases to created techniques used in genetic engineering. Out of this came the practices of electrophoresis and Southern blotting, which will be discussed later in this course, in order to identify certain DNA segments using hybridization probes. Recombinant DNA technology, used to make many synthetic drugs, has come out of molecular genetic study. Another commonly used technique in medicine to identify organisms without culturing them is called polymerase chain reaction—also a byproduct of molecular genetics. All of this culminated in the identification of the human genome, which created the field of genomics. Genomics takes the DNA molecule through the processes that make a functional protein.

The study of molecular genetics uses many techniques. Forward genetic techniques are specifically used to identify the genes or mutations that produce certain phenotypes in an organism. Genetic screening techniques will create random mutations in a genome to look for different phenotypes. Transformation techniques study antibiotic resistance in bacteria. Mutant genes can be identified as being dominant or recessive, while epistatic genes are mutant genes that mask another gene’s phenotype. DNA sequencing is then used to map where a certain mutation is located.

Reverse genetics is another aspect of molecular genetics that uses an intentional mutation in a gene to create and identify a different phenotype. This helps to identify what the function of the gene is supposed to be. It sometimes induces gene knockout, in which the entire gene is deleted. On the other hand, gene knock-in techniques can be used to add genes into the genome. These added genes are called transgenes and they usually result in a gain in function of the host. These reverse genetic techniques are generally faster than forward techniques.

Population genetics is another major field of genetic research, itself being part of the study of evolutionary biology. It studies things like the organism’s adaptation to the environment, the development of new species, and population structure from a genetic perspective. It has been helpful in identifying modern evolutionary theories. Instead of using phenotypes to study different populations, it relies on the genotype of an organism.

Population genetics was first created by combining biostatistics with Mendelian inheritance to identify issues related to the natural selection of some organisms over others. It relies on mathematical principles used to describe how populations are able to maintain some level of variation. According to population genetics, the variation in a population of organism is maintained by the action of many genes acting together. Out of this came the idea that the frequency of certain alleles in a population could change, leading to evolution. This was furthered by areas of study in animal breeding that resulted in inbreeding and what’s called genetic drift. Population genetics was developed after classical genetics but before molecular genetics.