Mendelian Genetics in Pea Plants

Mendel's Pea Plant Experiments

• Pea plants have a short generation time, enabling observation of multiple generations quickly.
• Mendel analyzed seven pairs of contrasting traits:
  • Flower color: purple or white
  • Flower position: axial or terminal
  • Seed color: yellow or green
  • Seed shape: round or wrinkled
  • Pod color: green or yellow
  • Pod shape: inflated or constricted
  • Plant height: tall or short

Monohybrid Cross

• P Generation: Mendel used true-breeding plants (homozygous) for traits. Example: crossed TT (tall) with tt (short).
• F1 Generation: All offspring were heterozygous (Tt), displaying the dominant trait (tall).
• F2 Generation: Self-pollination of F1 produced a 3:1 phenotypic ratio of tall to short plants.
• Conclusion: Traits are inherited as discrete units called genes, with alleles segregating during gamete formation (Law of Segregation).

Dihybrid Cross

• P Generation: Crossed true-breeding plants for two traits (YYRR with yyrr).
• F1 Generation: All offspring were heterozygous (YyRr), exhibiting dominant traits (yellow and round).
• F2 Generation: Resulting combinations included yellow round, green round, yellow wrinkled, and green wrinkled with a 9:3:3:1 ratio.

Mutations

• Somatic mutations: occur in non-reproductive cells, affecting individual health but not passed to offspring.
• Internal mutations: result from errors within the organism (e.g., DNA replication).
• External mutations: caused by external agents interacting with DNA.

Types of Gene Mutations

• Substitution: One base replaces another (e.g., sickle cell anemia).
• Insertion: Extra nucleotides added, often causing frameshift (e.g., beta-thalassemia).
• Deletion: Nucleotides skipped or excised, causing frameshift (e.g., certain cancers).
• Missense: Nucleotide change leads to amino acid change.
• Nonsense: Mutation produces a premature stop codon.
• Splice site: Affects RNA splicing, leading to abnormal proteins.

Genetic Disorders

• Hemophilia: Causes reduced blood clotting, leading to excessive bleeding.
• Phenylketonuria: Inherited disorder, excess phenylalanine is toxic to the nervous system.
• Sickle Cell Anemia: Caused by inherited faulty hemoglobin genes, leading to red blood cell shortages.
• Down Syndrome: Trisomy 21, an extra chromosome 21 leads to a total of 47 chromosomes.
• Edwards Syndrome (Trisomy 18) and Patau Syndrome (Trisomy 13): Both caused by extra chromosomes.
• Klinefelter Syndrome: Male with an extra X chromosome (XXY).
• Turner Syndrome: Female with a missing or partially missing X chromosome (XO).
• Cri-Du-Chat Syndrome: Deletion on chromosome 5, characterized by distinctive cat-like cry in affected infants.
• Prader-Willi and Wolf-Hirschhorn Syndromes: Genetic disorders caused by deletions on specific chromosomes.
• Fragile X Syndrome: Mutation in FMR1 gene affects brain development.
• Trisomy X: Females with an extra X chromosome.
• XYY Syndrome: Males with an extra Y chromosome.

Genetic Engineering

• Process of altering an organism's genetic makeup using recombinant DNA technology.
• Applications include the production of insulin, oil-eating bacteria for bioremediation, and selective breeding.
• Involves identifying, extracting, and inserting genes into host cells to produce GMOs.

Applications of Genetic Engineering

• Distant Hybridization: Transfer genes between distantly related species for desirable traits.
• Subunit, Recombinant, or Conjugate Vaccines: Contain parts of pathogens to stimulate immune response.
• mRNA Vaccines: Use messenger RNA to instruct cells to produce protective proteins.
• Diagnostic tools for genetic disorders and diseases (e.g., HIV testing).
• Production of therapeutic enzymes using recombinant DNA (e.g., urokinase for blood clots).
• Creation of transgenic animals, contributing to agricultural advancements (e.g., Dolly the sheep).

Other Applications of Biotechnology

• Stem Cell Therapy: Used to repair damaged tissues.
• Gene Therapy: Aims to replace dysfunctional genes or fix mutations by injecting genetic material.