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• Genetics


  The scientific study of genes and heredity - of how certain qualities or traits are passed from parents to offspring as a result of changes in DNA sequence
• Genetics forms one of the central pillars of biology and overlaps with many other areas, such as agriculture, medicine, and biotechnology
• Since the dawn of civilization, humankind has recognized the influence of heredity and applied its principles to the improvement of cultivated crops and domestic animals
• Genetics


  The study of genes at all levels, including the ways in which they act in the cell and the ways in which they are transmitted from parents to offspring
• DNA


  The chemical substance that genes are made of
• Gene action depends on interaction with the environment
• Green plants have genes containing the information necessary to synthesize the photosynthetic pigment chlorophyll

  • Chlorophyll is synthesized in an environment containing light
  • If a plant is placed in a dark environment, chlorophyll synthesis stops because the gene is no longer expressed
• Genetics as a scientific discipline stemmed from the work of Gregor Mendel


  Middle of the 19th century
• Mendel's units


  The basis for the development of the present understanding of heredity
• The word genetics was introduced by English biologist William Bateson


  1905
• Humankind must have been interested in heredity long before the dawn of civilization
• Curiosity about heredity


  • Based on human family resemblances such as similarity in body structure, voice, gait, and gestures
  • Instrumental in the establishment of family and royal dynasties
• Early nomadic tribes


  • Interested in the qualities of the animals that they herded and domesticated, and undoubtedly bred selectively
• Pangenesis


  Hypothesis devised by Hippocrates to account for the inheritance of acquired characteristics
• Hippocrates postulated that all organs of the body of a parent gave off invisible "seeds", which were like miniaturized building components and were transmitted during sexual intercourse, reassembling themselves in the mother's womb to form a baby
• Aristotle's ideas about the role of blood in procreation

  The origin of the still prevalent notion that the blood is involved in heredity
• Aristotle believed that the baby would develop under the influence of hereditary essences, rather than being built from the essences themselves
• Mendel's idea was that distinct differences between individuals are determined by differences in single yet powerful hereditary factors
• Genes


  The single hereditary factors identified as the basic unit of genetic information
• Copies of genes are transmitted through sperm and egg and guide the development of the offspring
• Genes are responsible for reproducing the distinct features of both parents that are visible in their children
• Genome


  The total number of genes contained in a cell
• Human cells


  • 46 chromosomes
  • 2 sex chromosomes (X, Y)
  • 22 pairs of body chromosomes (autosomes)
• Genotype


  The set of genes in our DNA responsible for a particular trait
• The term genotype was coined by the Danish botanist Wilhelm Johannsen


  1903
• Alleles


  The matching genes; one from the biological mother and one from the biological father
• Ploidy


  The number of copies of each chromosome found in a species
• Homozygous


  When both alleles are the same
• Heterozygous


  When the alleles are different
• Phenotype


  The observable traits and characteristics in an individual or organism
• Genotype contributes to phenotype, the degree to which depends on the trait
• Complex traits


  Traits that are influenced by additional factors such as environmental and epigenetic factors
• Epigenetics


  The study of how behaviors and environment can affect the way genes work
• Not all individuals with the same genotype look or act the same way because appearance and behaviour are modified by environmental and growing conditions
• Not all organisms that look alike necessarily have the same genotype
• Mendelian inheritance


  Traits that are determined exclusively by genotype and are typically inherited in a Mendelian pattern
• Gregor Mendel performed experiments with pea plants to determine how traits were passed on from generation to generation
• Dominant trait


  A trait that is expressed even if the individual is heterozygous for that trait
• Recessive trait


  A trait that is only expressed if the individual is homozygous for that recessive allele
• Punnett square


  A tool used to illustrate Mendelian inheritance patterns