Genetics and Agriculture: An Overview

Introduction to Genetics and Agriculture

• This video provides an overview of genetics and plant breeding in agriculture, especially regarding the 2021 agriculture policy.
• Topics covered include cell structure, cell division, genetic material, Mendelian genetics, plant breeding techniques, mutations, tissue culture, and plant biotechnology.

Cytology: Cell Structure and Division

• A cell is the basic structural, functional, and biological unit of living organisms, capable of self-replication.
• Cells were first discovered by Robert Hooke in 1665 using a compound microscope, observing cork.
• Anton van Leeuwenhoek was the first to observe living cells using a high-magnification microscope.
• Plant and animal cells differ in shape and structure, including the presence of a cell wall in plant cells.
• Prokaryotic cells have an undeveloped nucleus, like bacteria and cyanobacteria.
• Eukaryotic cells possess a well-developed nucleus and are found in plants and animals.
• Cytology is the study of cells.
• Cells are independent living components that perform essential functions internally.
• Robert Brown discovered the nucleus in cells.
• Unicellular organisms consist of one cell, while multicellular organisms consist of many cells.
• Cell theory, proposed by Schleiden and Schwann in 1839, states that all new cells arise from pre-existing cells.
• Mitosis was termed by Flemming, and meiosis was termed by Farmer and Moore.
• The smallest cell is bacteria (0.5 to 0.2 micrometers).
• The largest cell is an ostrich egg (75mm).
• Mycoplasma/PPLO are the smallest living organisms (Pleuro-Pneumonia Like Organisms).

Cellular Components: Cell Wall and Membrane

• The cell wall is a rigid outer layer in plant cells, composed mainly of cellulose, that protects and maintains the cell's shape.
• Cell wall components include the middle lamella (mainly calcium pectate), primary cell wall, and secondary cell wall.
• The cell membrane is a semi-permeable membrane enclosing the cell, composed of lipids, proteins, and carbohydrates.
• It plays a role in substance transportation into and out of the cell through processes like osmosis.

Protoplasm, Nucleus, and Cell Organelles

• Protoplasm includes the nucleus and cytoplasm.
• Cytoplasm is the substance filling the cell, excluding the nucleus.
• The nucleus, discovered by Robert Brown, is the control center of the cell and contains genetic material (chromosomes).
• Mitochondria are responsible for ATP production through the Krebs cycle and electron transport chain.
• Mitochondria is known as the "powerhouse of the cell."
• Its structure includes the outer membrane, inner membrane, cristae, and matrix.
• Plastids are organelles in plant cells that contain pigments, including chloroplasts, chromoplasts, and leucoplasts.
• Chloroplasts are the site of photosynthesis, containing grana (light reaction) and stroma (dark reaction).
• Cell organelles are small components within a cell with specific functions.
• The endoplasmic reticulum (ER) is a network facilitating transportation within the cell.
• Smooth ER is involved in lipid synthesis, and rough ER in protein synthesis due to ribosomes.
• Ribosomes are the site of protein synthesis.
• 70S ribosomes are in prokaryotes and some eukaryotic organelles, while 80S ribosomes are in eukaryotic cytoplasm.
• Golgi bodies, discovered by Camillo Golgi, act as the "traffic police," facilitating the transportation of cellular components and are part of the endomembrane system.
• Lysosomes are produced by Golgi bodies.
• They are known as "suicidal bags" due to hydrolytic enzymes like acid phosphatase.
• Peroxisomes are involved in photorespiration and carry out the glycolate mechanism.
• Glyoxysomes are responsible for the glyoxylate cycle in germinating seeds and convert stored lipids to carbohydrates.
• Vacuoles are large in plant cells and small in animal cells.
• They are enclosed by a membrane called the tonoplast.
• Centrioles are found only in animal cells and are involved in spindle fiber formation during cell division.

Cell Division: Mitosis and Meiosis

• Cell division is the process of forming new cells from pre-existing ones, including mitosis and meiosis.
• Mitosis is an equational division where the chromosome number remains the same.
• Mitosis results in two daughter cells.
• Its phases include interphase, prophase, metaphase, anaphase, telophase, and cytokinesis.
• Interphase is a resting phase consisting of G1, S, and G2 phases where the cell prepares for division.
• During the G1 phase, protein and RNA synthesis predominantly occurs.
• The S phase is for DNA synthesis.
• During the G2 phase, the cell prepares for cell division.
• During prophase, the nuclear apparatus starts to disappear, and chromosomes condense.
• During metaphase, chromosomes align at the equatorial plate.
• Anaphase involves the splitting of chromosomes and is the shortest phase.
• During telophase, the nuclear envelope reforms, reversing prophase.
• Cytokinesis is the division of cytoplasm.
• Cell plate formation and furrow formation are types of cytokinesis.
• Meiosis is a reduction division where the chromosome number is halved.
• Meiosis results in four daughter cells.
• It occurs in reproductive cells (gamete formation).
• Meiosis has two main stages: Meiosis I and Meiosis II.
• Meiosis I is a reductional division.
• Prophase I has five substages: leptotene, zygotene, pachytene, diplotene, and diakinesis, followed by metaphase I, anaphase I, and telophase I.
• Meiosis II is similar to mitosis.
• During leptotene, chromosomes begin to condense.
• During zygotene, synapsis begins.
• During pachytene, crossing over occurs, and tetrads form.
• During diplotene, chiasmata form.
• During diakinesis, chromosomes are fully condensed.

Chromosomes and Genetic Material

• A chromosome is a thread-like structure carrying genetic information.
• Strasburger discovered chromosomes, and Waldeyer coined the term.
• Karyotype is the number and appearance of chromosomes in the nucleus of a eukaryotic cell.
• Chromatin is a complex of DNA, RNA, and proteins that make up chromosomes.
• Histones are proteins around which DNA is wrapped in chromatin.
• A nucleotide is composed of a nucleoside + phosphoric acid.
• A nucleoside is composed of sugar + a nitrogenous base.
• Nucleic acids' basic components include a nitrogenous base, sugar, and phosphoric acid.
• Nitrogenous bases include purines (adenine (A), guanine (G)) and pyrimidines (cytosine (C), thymine (T), uracil (U)).

RNA and DNA

• RNA (Ribonucleic Acid) is found in the cytoplasm, nucleolus, and ribosomes.
• It is responsible for protein synthesis.
• RNA acts as genetic material in some viruses (the exception is the Cauliflower Mosaic Virus with dsDNA).
• Types of RNA include messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
• mRNA carries genetic information and makes up 5-10% of total RNA.
• tRNA transfers amino acids to the protein synthesis site and is also known as soluble RNA.
• rRNA is the most abundant and stable RNA, making up 80% of total RNA.
• DNA (Deoxyribonucleic Acid) has a double-stranded helical structure.
• Its bases are adenine, guanine, cytosine, and thymine.
• DNA is found in the nucleus and mitochondria.

Mutation

• A mutation is a sudden inheritable change in genetic material.
• A mutagen is a factor causing mutation and can be physical (temperature, radiation), chemical, or biological (bacteriophages).
• Radiation types include ionizing and non-ionizing radiation.
• A bacteriophage is a virus that infects bacteria.
• Hugo de Vries is the father of mutation.
• Types of mutation include gene mutation (changes in the genetic sequence) and chromosomal mutation (alterations in chromosome structure or number).
• Chromosomal aberration includes structural and numerical changes.
• Structural changes include deletion, duplication, translocation, and inversion.
• Numerical changes include aneuploidy (monosomy, trisomy) and euploidy.
• Deletion is the loss of a chromosome segment.
• Duplication is the repetition of a chromosome segment.
• Translocation is the transfer of a chromosome segment.
• Inversion is the reversal of a chromosome segment.
  • Monosomy is represented by (2n-1)
  • Nullisomy is represented by (2n - 2)
  • Trisomy is represented by (2n + 1)
  • Tetrasomy is represented by (2n + 2)
• Down Syndrome is trisomy at chromosome 21.
• Euploidy is a complete set added (haploid , triploid, etc...)
• Chemicals, and colchicine area treatment to induce Ploidy.

Ploidy and Colchicine

• Monoploid is represented by 'n'.
• Diploid is represented by '2n'.
• Autotriploid examples include banana, watermelon, and sugarcane.
• An allopolyploid example is wheat.
• Colchicine is a chemical used for inducing polyploidy.

Mendelian Genetics

• Mendelian genetics focuses on laws of inheritance.
• Laws include dominance, segregation, and independent assortment.
• Gregor Mendel conducted experiments on pea plants.
• Reasons for choosing pea plants include a short life cycle, a large number of offspring, and contrasting characters.
• Seven characters studied include plant height, flower position, flower color, seed shape, seed color, pod shape, and pod color.
• Plant height can be tall (dominant) or dwarf (recessive).
• Flower position can be axial (dominant) or terminal (recessive).
• Flower color can be purple (dominant) or white (recessive).
• Seed shape can be round (dominant) or wrinkled (recessive).
• Seed color can be yellow (dominant) or green (recessive).
• Pod color can be green or yellow.
• In a monohybrid cross, one character is involved; in a dihybrid cross, two characters are involved.
• Phenotypic is the physical appearance, and genotypic is the genetic constitution.
• F2 generation ratios for a monohybrid cross (phenotypic) is 3:1.
• F2 generation ratios for a monohybrid cross (genotypic) is 1:2:1.
• F2 generation ratios for a dihybrid cross (phenotypic) is 9:3:3:1.
• Homozygous individuals have the same alleles (TT or tt).
• Heterozygous individuals have different alleles (Tt).
• Multiple alleles involve single gene with more variations and is not always expressed.
• Gene action interactions include epistasis, complementary, supplementary, and additive interactions.
• Additive Gene Action: The ratio is 1:4:6:4:1
• Dominant Epistasis Gene Interaction: The ratio is 12:3:1
• Recessive Epistasis Gene Interaction: The ratio is 9:3:4
• Duplicate Gene Action: The ratio is 15:1
• Inhibitory Gene Action: The ratio is 13:3
• A hapten is a small molecule that elicits an immune response only when attached to a larger carrier.
• An antigen is a molecule that provokes an immune response.
• Linkage is the phenomenon of inheritance of linked genes.
  • Term coined by Bateson and Punnett.
• A test cross is a common method for detecting linkage.

Plant Breeding Techniques

• Pure line selection involves a single-cell fertilized homozygous line.
• It is used in self-pollinated crops (e.g., rice, wheat).
• Mass selection is based on phenotype selection and is used in cross-pollinated crops.
• Clonal selection involves progeny from a single plant produced through asexual reproduction.
• The progenies are called clones.
• The pedigree method is based on ancestral records and is used for genetic improvement of self-pollinated crops.
• Backcrossing involves crossing a hybrid with one of its parents with outcross and self-cross.
• A test cross involves crossing an F1 hybrid with the recessive parent.
• Incomplete dominance occurs when neither allele is fully dominant.
• Codominance occurs when both alleles are equally expressed (e.g., human blood groups).

Seed Production

• A seed is a fertilized ovule with the capacity for germination.
• The Seed Act passed in 1966 and implementation in 1969
• The National Seed Corporation was established in 1963
  • National seed act: 1966
  • Implementation: 1969
  • National Seed Corporation: 1963
• Seed types include breeder, foundation, certified and registered.
• Breeder seed is genetically pure seed developed by the original breeder and is gold in color.
• Foundation seed is produced from breeder seed and is white in color.
• Registered seed is produced from foundation or registered seed and is purple in color
• Certification: Seed from Seed association/Foundation
• Blue color

Seed Viability, Vigor, and Dormancy

• Seed viability is the ability of seeds to germinate.

• Tests include the potassium permanganate test and the tetrazolium test.

• The tetrazolium test uses 2,3,5-triphenyl tetrazolium chloride to indicate seed viability.

  • Seed will be red

• Seed Vigor is the ability of Seeds can emerge during stress conditions

• Isolation Distance:

  • Distance isolation is kept for - Genetics - Physical

• Orthodox seeds survive and store with low temperature such as cereals.

• Examples: - Cereals

• Recalcitrant seeds have a short life span due to the inability to withstand desiccation.

• • Seed Dormancy**

• Reasons*

• How we can change it* Low temperature causes it to crack.

• Seed Dormancy requires breaking for Hard seed coat: seed can be scarified.

• If due to hormonal: seed can be sprayed with GA3 ( gibberellic acid )

Molecular Genetics

• Transcription* DNA to mRNA
• Translation* mRNA to AA to protein