Lesson 1.1 Mendelian Laws of Inheritance

• Gregor Mendel's experiments laid the foundation for the study of transmission genetics by providing insights into the mechanisms of inheritance
• Genetics explains how traits are transmitted from parents to children
• Branches of Genetics:

  • Molecular genetics deals with DNA and gene expression and regulation
  • Cytogenetics deals with chromosome structure and behavior during cell division
  • Transmission genetics deals with different patterns of inheritance
  • Population genetics deals with how forces of evolution influence genes in populations
• Transmission genetics, also known as classical genetics, is the oldest subdiscipline of genetics that attempts to predict outcomes of reproduction
• Gregor Mendel, known as the Father of Genetics, performed experiments on garden peas (Pisum sativum) for his hybridization experiments. that led to the formulation of the laws of inheritance
• Pea plants were ideal for genetic studies because they exhibit vigorous growth, can self-fertilize, and can cross-fertilize
• Challenges faced by Mendel:

  • Previous notions of inheritance included Pangenesis, Homunculus theory, and Blending theory
  • Pangenesis believed that seeds are produced in different organs and gather to form offspring
  • Homunculus theory suggested that sperm cells bear a homonculus or little man
  • Blending theory stated that traits of parents blend in each generation of offspring
• Mendel's paper, "The Experiments on Plant Hybridization," was rediscovered independently by Hugo de Vries, Carl Correns, and Erich von Tschermak in the 1900s
• Review of Genetic Terminologies:

  • Chromosome: consists of a DNA molecule, serving as the repository of genetic information
  • Genes: basic units of heredity controlling the expression of biological characteristics
  • Characteristic: Is a heritable feature of an organism
  • Alleles: alternative forms of a gene
  • Genotype: set of alleles possessed by an organism
  • Homozygous: If the alleles are identical
  • Heterozygous: If the alleles are different
  • Phenotype: actual manifestation of genotypes into observable traits
• Monohybrid Cross:

  • Principle of Dominance: alleles segregate during gamete formation
  • Genotypes: TT (tall), Tt (tall), tt (dwarf)
  • Phenotypic Ratio: 3/4 tall: 1/4 dwarf
• Dihybrid Cross:

  • Involves two pairs of contrasting traits
  • Both parents must also be true breeding or homozygous
  • Law of Independent Assortment: alleles from different genes segregate independently
  • Phenotypic Ratio in F2 generation: 9:3:3:1
• Genetics is the study of inheritance and variation in organisms, with transmission genetics focusing on the mechanisms or patterns of inheritance
• Genes control the expression of characteristics, with alleles being alternative forms of a gene. Genes can be dominant or recessive, and in a heterozygous individual, the dominant allele masks the recessive allele
• Transmission genetics is a pioneering field in genetics, exploring the mechanisms and patterns of inheritance
• Review of Genetic Terminologies:

  
  

  Our chromosomes occur in pairs

  called homologous chromosomes.

  Paternal (from the father or male parent)

  Maternal (from the mother or female parent)

  Genes occur in pairs, a pair of genes control a particular characteristic
• Law of Independent Assortment:

  The alleles from different genes are sorted into the gametes independently of each other. Thus, the inheritance of these two genes become independent.