Introduction to Genetics

•We all possess genes that influence our lives in significant ways.

•Genes affect our height, weight, hair color, and skin pigmentation.

•They influence our susceptibility to many diseases and disorders and even contribute to our intelligence and personality.

•Genes are fundamental to who and what we are.

•Even though the science of genetics is not a very old field, Societies have understood hereditary nature of traits and have practiced genetics for thousands of years.

•Hopi Native Americans: Black Mesa northeastern Arizona •Among the Hopis were 11 white people—not Caucasians, but actually white Hopi Native Americans. •These persons had a genetic condition known as albinism •The genetic basis of albinism was first described by Archibald Garrod, who recognized in 1908 that the condition was inherited as an autosomal recessive trait albinism type 2, due to a defect in the OCA gene on chromosome 15. •The first evidence that people understood and applied the People with albinism were considered pretty, clean, and intelligent. •Having a number of people with albinism in one’s village was considered a good sign, a symbol that the people of the village contained particularly pure Hopi blood. •Albinos performed in Hopi ceremonies and assumed positions of leadership within the tribe, often becoming chiefs, healers, and religious leaders

•The rise of agriculture began when people started to apply genetic principles to the domestication of plants and animals •The Green Revolution, which expanded food production throughout the world in the 1950s and 1960s, relied heavily on the application of genetics •genetically engineered corn, soybeans, and other crops constitute a significant proportion of all the food produced worldwide

The pharmaceutical industry is another area in which genetics plays an important role. •Numerous drugs and food additives are synthesized by fungi and bacteria that have been genetically manipulated to make them efficient producers of these substances.

The biotechnology industry employs molecular genetic techniques to develop and mass produce substances of commercial value. •Growth hormone, insulin, and clotting factor are now produced commercially by genetically engineered bacteria

Genetics plays a critical role in medicine. •many diseases and disorders have a hereditary component, including genetic disorders such as sickle-cell anemia and Huntington disease as well as many common diseases such as asthma, diabetes, and hypertension. •Advances in molecular genetics have resulted not only in important insights into the nature of cancer but also in the development of many diagnostic tests.

Gene therapy—the direct alteration of genes to treat human diseases—has now been carried out on thousands of patients.

•Genetics provides one of biology’s unifying principles: all organisms use genetic systems that have a number of features in common.

Evolution, is genetic change taking place through time; so the study of evolution requires an understanding of genetics.

Developmental biology relies heavily on genetics: tissues and organs form through the regulated expression of genes.

•Even fields as taxonomy, ecology, and animal behavior are making increasing use of genetic methods.

•The study of almost any field of biology or medicine is incomplete without a thorough understanding of genes and genetic methods.

•Life on Earth exists in a tremendous array of forms and features almost in every environment •Life is characterized by adaptation: many organisms are exquisitely suited to the environment in which they are found. •There are new forms of life emerging, old forms disappearing, and existing forms changing. •A complete set of genetic instructions for any organism is its genome, and all genomes are encoded in nucleic acids—either DNA or RNA. •The coding system for genomic information also is common to all life •the processes by which genetic information is copied and decoded are remarkably similar for all forms of life.

•These common features of heredity suggest that all life on Earth evolved from the same primordial ancestor that arose between 3.5 billion and 4 billion years ago. •Biologist Richard Dawkins describes life as a river of DNA that runs through time, connecting all organisms past and present. •That all organisms have similar genetic systems means that the study of one organism’s genes reveals principles that apply to other organisms. •Investigations of how bacterial DNA is copied (replicated), for example, provide information that applies to the replication of human DNA. •It also means that genes will function in foreign cells, which makes genetic engineering possible.

•these similar genetic systems are also the basis for diseases such as AIDS (acquired immune deficiency syndrome), in which viral genes are able to function with alarming efficiency in human cells. •Life’s diversity and adaptation are products of evolution, which is simply genetic change through time. •Evolution is a two-step process: first, genetic variants arise randomly and, then, the proportion of particular variants increases or decreases. •Genetic variation is therefore the foundation of all evolutionary change and is ultimately the basis of all life as we know it.

•Genetics, the study of genetic variation, is critical to understanding the past, present, and future of life.

Traditionally, the study of genetics has been divided into major subdisciplines: transmission genetics, molecular genetics, and population genetics

•Also known as classical genetics, transmission genetics encompasses the basic principles of heredity and how traits are passed from one generation to the next.

•the focus is on the individual organism—how an individual organism inherits its genetic makeup and how it passes its genes to the next generation. •It is the oldest discipline in the field of genetics-experiments on Mendelian inheritance by Gregor Mendel who identified the basic mechanisms of heredity. • A key discovery of classical genetics in eukaryotes was genetic linkage. •The observation that some genes do not segregate independently at meiosis broke the laws of Mendelian inheritance •map genes to a location on the chromosomes

Molecular genetics

•concerns the chemical nature of the gene itself: how genetic information is encoded, replicated, and expressed. •It includes the cellular processes of replication, transcription, and translation—by which genetic information is transferred from one molecule to another •and gene regulation—the processes that control the expression of genetic information. •The focus in molecular genetics is the gene—its structure, organization, and function.

Population genetics

explores the genetic composition of groups of individual members of the same species (populations) and how that composition changes over time and geographic space. •Because evolution is genetic change, population genetics is fundamentally the study of evolution. •The focus of population genetics is the group of genes found in a population.

Other fields:

Behavioural genetics

also commonly referred to as behaviour genetics, • is the field of study that examines the role of genetic and environmental influences on animal(including human) behaviour. •Behavioural geneticists study the inheritance of behavioural traits. In humans, this information is often gathered through the use of the twin study or adoption study. In animal studies, breeding, transgenesis, and gene knockout techniques are common.  Psychiatric genetics is a closely related field.

Developmental biology

 is the study of the process by which animals and plants grow and develop

 In animals most development occurs in embryonic life, but it is also found in regeneration, asexual reproduction and metamorphosis, and in the growth and differentiation of stem cells in the adult organism.

In plants, development occurs in embryos, during vegetative reproduction, and in the normal outgrowth of roots, shoots and flowers.

•Practical outcomes from the study of animal developmental biology have included in vitro fertilization, •the understanding of risks from substances that can damage the fetus (teratogens), and the creation of various animal models for human disease which are useful in research.

•Developmental Biology has also help to generate modern stem cell biology which promises a number of important practical benefits for human health.

Conservation genetics 

•is an interdisciplinary science that aims to apply genetic methods to the conservation and restoration of biodiversity. •Researchers involved in conservation genetics come from a variety of fields including population genetics, molecular ecology, biology, evolutionary biology, and systematics.

•Genetic diversity important in conservation of biodiversity •Conservation of genetic variability is important to the overall health of populations because decreased genetic variability leads to increased levels of inbreeding, and reduced fitness


•Ecological genetics 

•is the study of genetics in natural populations. •Research in this field is on traits of ecological significance—that is, traits related to fitness, which affect an organism’s survival and reproduction. • Examples might be: flowering time, drought tolerance, polymorphism. • Changes in the populations at different times and places will be noted, and the pattern of mortality in these populations will be studied. •Research is often done on insects and other organisms that have short generation times.

Medical genetics

• is the branch of medicine that involves the diagnosis and management of hereditary disorders. Medical genetics differs from human genetics in that human genetics is a field of scientific research that may or may not apply to medicine, while medical genetics refers to the application of genetics to medical care

Clinical genetics

•is the practice of clinical medicine with particular attention to hereditary disorders. Referrals are made to genetics clinics for a variety of reasons, including birth defects, developmental delay, autism, epilepsy, short stature, and many others. •Metabolic (or biochemical) genetics involves the diagnosis and management of inborn errors of metabolism in which patients have enzymatic deficiencies that perturb biochemical pathways involved in metabolism of carbohydrates, amino acids, and lipids.


• is the study of chromosomes and chromosome abnormalities.


•Literally, it means “the creation of something which creates.” In the context of biotechnology, metagenics is the practice of engineering organisms to create a specific enzyme, protein, or other biochemicals from simpler starting materials.

•principles of heredity in earlier times is found in the domestication of plants and animals, which began between approximately 10,000 and 12,000 years ago.

•The world’s first agriculture is thought to have developed in the Middle East, in what is now Turkey, Iraq, Iran, Syria, Jordan, and Israel, where domesticated plants and animals were major dietary components of many populations by 10,000 years ago.

•The first domesticated organisms included wheat, peas, lentils, barley, dogs, goats, and sheep

•By 4000 years ago, sophisticated genetic techniques were already in use in the Middle East.

•Assyrians and Babylonians developed several hundred varieties of date palms that differed in fruit size, color, taste, and time of ripening

•The ancient Greeks gave careful consideration to human reproduction and heredity

concept of pangenesis

•This concept suggested that specific pieces of information travel from various parts of the body to the reproductive organs, from which they are passed to the embryo •Pangenesis led the ancient Greeks to propose the notion of the inheritance of acquired characteristics, in which traits acquired in one’s lifetime become incorporated into one’s hereditary information and are passed on to offspring

Preformationism: According to preformationism, inside the egg or sperm there exists a tiny miniature adult, a homunculus  Which simply enlarges during development

•Preformationism meant that all traits would be inherited from only one parent—from the father if the homunculus was in the sperm or from the mother if it was in the egg. •Another early notion of heredity was blending inheritance, which proposed that offspring are a blend, or mixture, of parental traits •Developments in cytology (the study of cells) in the 1800s had a strong influence on genetics.

•Weismann proposed the germ-plasm theory, which holds that the cells in the reproductive organs carry a complete set of genetic information that is passed to the egg and sperm

•The year 1900 was a watershed in the history of genetics. Gregor Mendel’s pivotal 1866 publication on experiments with pea plants, which revealed the principles of heredity, was rediscovered

•Walter Sutton (1877–1916) proposed in 1902 that genes are located on chromosomes.

•Thomas Hunt Morgan (1866–1945) discovered the first genetic mutant of fruit flies in 1910 and used fruit flies to unravel many details of transmission genetics.

•James Watson (b. 1928) and Francis Crick (1916–2004), along with Maurice Wilkins (1916–2004) and Rosalind Franklin (1920–1958), described the three dimensional structure of DNA in 1953, ushering in the era of molecular genetics

•By 1966, the chemical structure of DNA and the system by which it determines the amino acid sequence of proteins had been worked out.

•Methods for rapidly sequencing DNA were first developed in 1977, which later allowed whole genomes of humans and other organisms to be determined.

•PCR was developed by Kary Mullis (b. 1944) and others in 1983. •This technique is now the basis of numerous types of molecular analysis.

•In 1990, the Human Genome Project was launched.

•By 1995, the first complete DNA sequence of a free-living organism—the bacterium Haemophilus influenzae—was determined, and the first complete sequence of a eukaryotic organism (yeast) was reported in 1996. • A rough draft of the human genome sequence was reported in 2000, with the sequence essentially completed in 2003