History and Development of Genetics
- The word 'genetics' stems from the ancient Greek γενετικός (genetikos) meaning genitive/generative, which in turn derives from γÎνεσις (genesis) meaning origin.
- The observation that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding.
- The modern science of genetics began with the work of Gregor Mendel in the mid-19th century.
- Imre Festetics, a Hungarian noble, used the word 'genetic' in a hereditarian context before Mendel.
- Festetics argued that organisms inherit their characteristics, not acquire them.
- Mendel's work provided examples where traits were definitely not blended after hybridization, showing that traits are produced by combinations of distinct genes.
- The importance of Mendel's work did not gain wide understanding until 1900, after his death.
- William Bateson coined the word 'genetics' in 1905.
- Bateson popularised the usage of the word 'genetics' to describe the study of inheritance.
Molecular Genetics
- DNA is the molecular basis for biological inheritance.
- Genes are known to exist on chromosomes, which are composed of both protein and DNA.
- Scientists did not know which of the two components, protein or DNA, was responsible for inheritance.
- Nettie Stevens discovered that sex is a chromosomal factor and is determined by the male.
- Thomas Hunt Morgan argued that genes are on chromosomes based on observations of a sex-linked white eye mutation in fruit flies.
Gene Structure and Function
- Gene structure and function are studied within the context of the cell, the organism, and the population.
- Variation and distribution of genes are important areas of study in genetics.
- Gene structure and function play a role in traits, behavior, and development.
- Molecular genetics is a subfield of genetics that focuses on the structure and function of genes.
- Epigenetics is another subfield of genetics that studies how gene expression can be influenced by factors other than changes in DNA sequence.
Nature vs. Nurture
- Genetic processes work in combination with an organism's environment and experiences to influence development and behavior.
- The intracellular or extracellular environment of a living cell or organism can affect gene transcription.
- The example of genetically identical corn seeds growing to different heights in different climates illustrates the interaction between genes and the environment.
- The study of nature vs. nurture explores the relative contributions of genetics and environmental factors in shaping traits and behavior.
- Genetics has provided insights into the complex interplay between nature and nurture in determining an organism's characteristics.
DNA Structure and Inheritance
- Frederick Griffith discovered transformation in 1928.
- Avery-MacLeod-McCarty experiment identified DNA as the molecule responsible for transformation in 1944.
- Hershey-Chase experiment confirmed DNA as the genetic material of viruses in 1952.
- James Watson and Francis Crick determined the structure of DNA in 1953.
- DNA structure showed how genetic information is encoded in nucleotide sequences.
- DNA is used as a template to create messenger RNA (mRNA).
- mRNA carries the genetic code for protein production.
- Nucleotide sequence of mRNA determines the amino acid sequence in protein.
- Translation between nucleotide sequences and amino acid sequences is known as the genetic code.
- DNA controls the process of protein production through mRNA.
- Tomoko Ohta proposed the nearly neutral theory of molecular evolution in 1973.
- Frederick Sanger developed chain-termination DNA sequencing in 1977.
- Kary Banks Mullis invented the polymerase chain reaction (PCR) in 1983.
- Human Genome Project sequenced the human genome in 2003.
- Department of Energy, NIH, and Celera Genomics also contributed to genome sequencing.
- Gregor Mendel studied segregation of heritable traits in pea plants.
- Inheritance occurs through passing discrete heritable units called genes.
- Each individual plant has two copies of each gene, inherited from each parent.
- Dominant and recessive alleles determine observable traits (phenotypes).
- Mendel's first law or the Law of Segregation explains the random inheritance of alleles.
- Geneticists use symbols and diagrams to describe inheritance.
- Genes are represented by letters, with + symbol for non-mutant allele.
- Punnett square is a common diagram used to predict cross-breeding results.
- Pedigree charts are used to represent the inheritance of traits in humans.
- Multiple generations and relationships are shown in pedigree charts.
- DNA is composed of deoxyribose, a phosphate group, and four types of bases: adenine, cytosine, guanine, and thymine.
- Bases pair specifically (T&A, C&G) between two backbones, forming like rungs on a ladder.
- Nucleotides connect to make long chains of DNA.
- DNA exists as a double-stranded molecule, coiled into a double helix structure.
- Each nucleotide in DNA pairs preferentially with its partner nucleotide on the opposite strand.
- DNA wraps around proteins called histones to form chromosomes.
- Genes exist as stretches of sequence along the DNA chain.
- Bacteria have a single circular genophore, while eukaryotic organisms have DNA arranged in multiple linear chromosomes.
- Chromatin, composed of nucleosomes, organizes and controls access to DNA.
- The full set of hereditary material in an organism is called the genome.
- Nonchromosomal genes can be found outside of the nucleus in organisms like plants (chloroplasts) and other organisms (mitochondria).
- These genes can be passed on by either partner in sexual reproduction.
- Nonchromosomal genes control a variety of hereditary characteristics that replicate throughout generations.
- Ruth Sager helped in the discovery of nonchromosomal genes.
- These genes remain active throughout generations.
- Most animals and many plants are diploid, containing two copies of every gene
Genetics is the study of genes, genetic variation, and heredity in organisms. It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar working in the 19th century in Brno, was the first to study genetics scientifically. Mendel studied "trait inheritance", patterns in the way traits are handed down from parents to offspring over time. He observed that organisms (pea plants) inherit traits by way of discrete "units of inheritance". This term, still used today, is a somewhat ambiguous definition of what is referred to as a gene.
Trait inheritance and molecular inheritance mechanisms of genes are still primary principles of genetics in the 21st century, but modern genetics has expanded to study the function and behavior of genes. Gene structure and function, variation, and distribution are studied within the context of the cell, the organism (e.g. dominance), and within the context of a population. Genetics has given rise to a number of subfields, including molecular genetics, epigenetics and population genetics. Organisms studied within the broad field span the domains of life (archaea, bacteria, and eukarya).
Genetic processes work in combination with an organism's environment and experiences to influence development and behavior, often referred to as nature versus nurture. The intracellular or extracellular environment of a living cell or organism may increase or decrease gene transcription. A classic example is two seeds of genetically identical corn, one placed in a temperate climate and one in an arid climate (lacking sufficient waterfall or rain). While the average height of the two corn stalks may be genetically determined to be equal, the one in the arid climate only grows to half the height of the one in the temperate climate due to lack of water and nutrients in its environment.
From Ancient Greek γένεσις (génesis, “origin”). Coined by English biologist William Bateson in 1905 in a letter to zoologist Adam Sedgwick, and first used publicly by Bateson at a lecture to the International Conference on Plant Hybridization in 1906.
