genetics

• Gregor Mendel


  Father of Genetics
• Mendel's experiment


  Developed the fundamental principles of inheritance
• Mendel chose the garden pea plant, Pisum sativum and crossed it with other pea plants that had different contrasting characteristics
• Mendel's laws


  Established the principle of inheritance, which introduced the idea that inherent characteristics and genetic information are carried by discrete units known as genes
• Genes consist of DNA which are found in chromosomes that segregate independently during the formation of gametes and unite randomly to form an offspring
• Mendel simply wanted to create hybrid pea plants and meticulously observe the outcome, but his discoveries soon laid the foundation for the modern study of heredity
• Genetics is a science that involves the study of heredity, the passing of traits from parents to offspring
• Mendel was successful in determining the basic laws of heredity because of his experimental method
• Pea plants


  • Have many traits with two distinct forms and no intermediates
  • Are small and abundant
  • Mature quickly
  • Reproduce in large numbers
  • Mating can be controlled by using either self-fertilization or cross-fertilization
• Mendel's experiment procedure


  Use self-fertilization for several generations to ensure that parental generations are true-breeding

  2. Cross-fertilize of two contrasting P generation (parental generation) plants, with offspring known as the F1 generation (1st filial generation)

  3. Allow F1 generation to self-fertilize, producing the F2 generation (2nd filial generation)
• Mendel observed that traits could be expressed in simple ratios
• When Mendel crossed one purebred yellow seed and one purebred green seed for the parental generation, it resulted in an F1 generation that consisted only of yellow seeds
• Dominant trait


  The trait that is expressed in the F1 generation
• Recessive trait


  The trait that is masked by the dominant trait
• The F2 generation always showed both traits in a 3:1 ratio, in which one offspring exhibited the recessive trait
• Alleles


  Gene variants
• Law of Segregation


  During the formation of gametes, the pairs of alleles for a specific trait separate from one another and result in gametes that carry only a single inheritable trait
• Homozygous


  When both alleles in a single pair are similar
• Heterozygous


  When alleles for the same trait are dissimilar
• Homozygous dominant


  Represented by the same two letters in uppercase form (e.g., AA)
• Homozygous recessive


  Represented by the same two letters in the lowercase form (e.g., aa)
• Heterozygous


  Represented by one uppercase form and one lowercase form of the same letter (e.g., Aa)
• Genotype


  The complete combination of alleles for a particular gene
• Phenotype


  Observable physical traits inherited by the offspring
• Law of Dominance


  In a cross between two parents that are pure for a particular trait, one allele will be dominant over the other
• Steps to complete a Punnett square

  Construct a box with four smaller squares inside, then determine the parental genotypes of the crosses

  2. Write the possible gametes from one parent along the top of the square, and the possible gametes of the other parent along the left side

  3. Combine each allele along the top with each allele along the left side, placing them in their respective boxes

  4. Calculate the genotypic and phenotypic ratios of the crosses
• Mendel observed that in the process of gamete formation, the alleles of particular genes are inherited independently from one another
• Law of Independent Assortment

  The alleles of the genes in one gamete are different from the alleles of the genes in another gamete
• Dihybrid cross


  Involves two pairs of contrasting traits
• In a dihybrid cross, the cross resulted in an F1 generation with only yellow round seeds, and the F2 generation exhibited a phenotypic ratio of 9:3:3:1 and genotypic ratio of 1:2:1:2:4:2:1:2:1
• Steps to complete Punnett squares for the following crosses

  Ee x ee

  2. RR x rr

  3. Ss x Ss
• Pedigree


  A chart that traces the history of traits passed on among several generations of a family
• Pedigrees are used to trace the passing of an allele from parents to offspring and to detect which members of the family are afflicted with a genetic disorder
• Mendel's study of inheritance dealt with simple, independently-segregating traits in pea plants
• Mendel's work does not encompass all possible inheritance patterns that are recognized in the scientific field today
• Non-Mendelian patterns of inheritance


  Inheritance patterns that deviate from the dominant-recessive relationships that Mendel had observed in genotypes and phenotypes
• Non-Mendelian genetics


  • Incomplete dominance
  • Codominance
  • Multiple alleles
  • Polygenic inheritance
• Incomplete dominance


  The combination or blending of phenotypes in a heterozygous organism
• Incomplete dominance


  • Wavy hair in humans (blending of curly and straight hair)
• Codominance


  The heterozygous phenotype is a distinct combination of traits that differ from the homozygous phenotypes