Mendelian Genetics

• GREGOR MENDEL (1822-1884)
• He was an Australian monk at the distinguished monastery of St. Thomas in the town of Brünn, now Bruno in the Czech Republic
• He was a high school teacher in physics and natural history who spent his free time conducting biological experiments in a small garden near the monastery
• He carried out his famous experiments on crosses of garden peas (Pisum sativum) from 1856 to 1863
• HEREDITY


  Transmission of trait from parents to offspring; comes from the Greek word "hereditas" which means heirship
• TRAIT


  Distinguishing quality or characteristics
• GENES


  Unit in a chromosome that codes for a specific trait
• GENETICS


  The study of how traits are passed from parent to offspring
• He studied pea plants and their characteristics which include the flower color, flower position, seed color, seed shape, pod color, and length of stem
• For more than 10 years, Mendel experimented with thousands of pea plants
• He reported all his findings to a local natural history society, which then published the findings and interpretations of his research in its scientific journal in 1866
• He was called the "Father of Genetics"
• WHY MENDEL CHOOSE PEA PLANTS?

  Because they grow easily and reproduce quickly
• Pea plants have many varieties, but each trait studied by Mendel only had two
• He concluded that each inherited trait is controlled by two factors, and that when organisms reproduce, the gametes contribute a factor for each trait
• Mendel came up with an important hypothesis that did fit his observations
• He discovered that genes can exist in alternative forms called "alleles"
• Organisms have two alleles for each trait
• DOMINANT ALLELES


  Alleles that can hide the expression of other alleles. It is represented by a capital letter or uppercase
• RECESSIVE ALLELES


  Alleles whose expression can be masked. It is represented by a small letter or lowercase
• HOMOZYGOUS TRAIT


  If both alleles are the same, the organism is homozygous for the trait. Two copies of the same gene
• HETEROZYGOUS TRAIT


  If both alleles are different, the organism is heterozygous for that trait. Two different genes
• The upper-case letter is always written before the lower-case letter
• GENOTYPES


  The alleles of all the genes in the chromosome of an organism. The genetic makeup of an organism, or a type of genes. It is represented by letters
• PHENOTYPES


  The external appearance or expression of the genetic make-up/ inherited traits. Observable physical characteristics of an organism attributable to the expression of its genotype
• GENOTYPIC RATIO


  Shows the different outcomes you can get from a genetic cross
• PHENOTYPIC RATIO


  Shows the varied outcomes that result from a genetic cross and is based on physical appearance alone. But it can also be influenced by the environment
• P₁


  Refers to the parental generation
• F₁ and F₂


  Successive generations, the offspring of the parent
• Hybrid


  Offspring of crosses between pure parents with contrasting traits
• MENDEL'S EXPERIMENT


  1. Production of the pure-breeding strains of pea plants

  2. Crossing of two different varieties of pure breeding strains

  3. Crossing of the F1 generations
• Mendel found out that the garden peas all produced purple-colored flowers in the F1 generation
• In the F2 generation, 75% of the garden peas had purpled-colored flowers and 25% had white-colored flowers
• The white-colored flowers that did not appear in the F1 generation appeared in a ratio of 3:1
• LAW OF SEGREGATION


  The two factors for each trait separate from each other during meiosis when gametes are formed
• LAW OF INDEPENDENT ASSORTMENT


  The factors for one trait separate independently from other factors of other traits. The inheritance of one trait does not influence the inheritance of another
• LAW OF DOMINANCE


  One factor in the pair of traits dominates or masks the other. A trait will not appear in the offspring due to traits being suppressed by dominant traits
• PUNNETT SQUARE


  A tool used in identifying and predicting traits among individuals who are genetically related. It is used to predict the possible outcomes of genotypes and phenotypes of offspring
• MONOHYBRID CROSS


  A method of finding out the inheritance pattern of a trait between two single organisms. It is defined as the cross happening in the F1 generation offspring of parents differing in one trait only
• MONOHYBRID INHERITANCE


  The inheritance of a single characteristic