Mendel's Law of Inheritance

• Gregor Johann Mendel

  Austrian Monk
• Gregor Johann Mendel

  • Born in Czech Republic in 20 July 1822
  • Studied the inheritance in sweet pea plants (Pisum sativum)
  • Developed the law of inheritance, which is now called as Mendel's Principles
  • Mendel's work was not recognized until the turn of the 20th century
  • He died on 6 January 1884
• Trait

  Any characteristic that can be passed from parent to offspring
• Heredity

  Passing of traits from parent to offspring
• Genetics

  Study of heredity
• Genotypes

  Genetic makeup of an organism (Organism's complete set of genes)
• Phenotypes

  The physical appearance of an organism with respect to a trait, such as yellow seeds
• Dominant trait

  A trait expressed preferentially over another trait. It is represented with a capital letter
• Recessive trait

  The opposite of dominant. A trait that is preferentially masked. It is represented with the same letter as the respective dominant trait but with lower case
• Test cross

  A cross of an individual organism of dominant phenotype but unknown genotype and an organism with a homozygous recessive genotype (and phenotype). It is generally a cross involving a homozygous recessive individual
• Reciprocal cross

  Using male and female gametes for two different traits, alternating the source of gametes
• Genes

  A basic unit of heredity and a sequence of nucleotides in DNA that encodes the synthesis of a gene product, either RNA or protein
• Alleles

  Two forms of a genes (dominant & recessive)
• Dominant genes

  Stronger of two genes expressed in the hybrid. It is represented by a capital letter, e.g. for Tall variety, dominant allele will be represented by 'T'
• Recessive Genes

  Genes that shows up less often in a cross. It is represented by a lowercase letter, e.g. for Tall variety, recessive allele will be represented by 't'
• Genotype

  Gene combination for a trait, e.g. TT, Tt, tt, RR, Rr, rr, etc.
• Phenotypes

  The physical feature resulting from a genotype, e.g. Tall, Dwarf, Red, White, etc.
• Genotypes

  • Homozygous genotype
  • Heterozygous genotype
• Homozygous genotype

  Gene combination involving two dominant or two recessive genes, e.g. TT, RR, tt, rr, etc. It is also called 'pure'
• Heterozygous genotype

  Gene combination of one dominant and one recessive genes, e.g. Tt, Rr, etc. It is also called hybrid
• Types of Genetic Crosses

  • Monohybrid cross
  • Dihybrid cross
  • Trihybrid cross
• Monohybrid cross

  Cross involving a single trait, e.g. flower color, seed shape, eye color, etc.
• Dihybrid cross

  Cross involving two traits, e.g. flower color and plant height, eye color and abdomen color of the Drosophila melanogaster, eye color and hair color in the human, etc.
• Trihybrid cross

  Cross involving three traits or alleles belonging to three different genes, e.g. plant size, pod color and seed shape of a Sweet pea plant
• Generation in a Crossing

  • Parental P1 Generation
  • F1 Generation
  • F2 Generation
• Parental P1 Generation

  The parental generation in a breeding experiment
• F1 Generation

  The first-generation of offspring in a breeding experiment. It is also called 1st filial generation. It is derived from the breeding male and female of P1 generation
• F2 Generation

  The second-generation offspring in a breeding experiment. It is also called as 2nd filial generation. It is derived from breeding male and female individual of F1 generation
• Punnett Square

  A square diagram used to predict the genotypes of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the method in 1905

  
• Mendel's Law

  • Law of Dominance

  Law of Independent Assortment

  Law of Segregation
• Law of Dominance

  Hybrid offspring inherit only the dominant trait in the phenotype. The allele that are suppressed are called the recessive traits, while the alleles that determine the traits are called as the dominant traits
• Law of Independent Assortment

  A pair of traits segregates independently of another pair during gamete formation. It ensures equal opportunity of different traits to occur together
• Law of Segregation

  Two copies of hereditary factors segregate during the production of gametes so that offspring acquire one factor from each parent. In other words, allele pairs segregate during the formation of gamete and reunite randomly during fertilization
• Incomplete Dominance

  Both alleles of a gene at a locus are partially expressed, often resulting in an intermediate or different phenotype. F1 hybrids will have an appearance in between the two parental varieties, such as appearance of flower color in Snapdragon flower
• Incomplete Dominance

  • Cross: Red (RR) x White (rr)

  Offspring (F1): All Rr = Pink
• Codominance

  Two versions (alleles) of the same gene are expressed separately to yield different traits in an individual, such as blood type