DNA and Genetics in Agricultural Biotechnology

1. DNA and Genetics in Agricultural Biotechnology Objective 13.01: Discuss the structure and function of DNA in relation to sexual reproduction in organisms.

2. Structure of DNA • The genetic material of ALL LIFE on this planet is made up of only six components • Sugar molecule (deoxyribose) • Phosphate group • Four nitrogen containing bases • Adenine • Guanine • Cytosine • Thymine

3. Nucleotide • 1. Definition- a single molecule of DNA comprised of 2 basic parts made from 3 distinct molecules. • The building block of the DNA molecule, also called a deoxynucleotide Phosphate Deoxyribose Sugar Nitrogen Base

4. Nucleotide • a. Sugar / Phosphate Backbone • i) Composed of deoxyribose sugar and a simple phosphate molecule. • ii) Forms a strong bond that creates the backbone of a DNA strand. • iii) EXACLTY THE SAME IN ALL DNA.

5. Nucleotide Hydrogen Bonds • b. Nitrogenous Base • i) Bond with complimentary bases in other nucleotides to form the rungs of the DNA ladder. (zip DNA together) • ii) ONLY 4 TYPES IN ALL DNA- Adenine, Cytosine, Guanine, & Thymine. • iii) Adenine & Thymine bond only with each other. • iv) Cytosine & Guanine bond only with each other. Thymine Adenine Guanine Cytosine Hydrogen Bonds

6. DNA Form Sugar Phosphate Backbone Sugar Phosphate Backbone Nitrogenous Base Pairs • 1. DNA nucleotides combine in cells to form long strands in the shape of a double helix. (looks like a twisted ladder) • a. Nucleotides bond at two spots: • i) Sugar / Phosphate molecules form the backbone. (outside rails) • ii) Nitrogenous bases bond in the middle. (steps or rungs) • iii) Hydrogen bonds between nitrogenous bases are MOST EASILY broken. • b. The order of the nucleotides is the determining factor in the expression of genes in organisms. Single Nucleotide

7. DNA Form • Two sugar phosphate backbones lie side by side • One arranged 5’-3’ • The opposite must be arranged 3’-5’ • Therefore the bases are perfectly reflected of each other

8. Characteristics of DNA • When the structure was first proposed by Watson and Crick (1953) • Thought to be single helix and unfixed • We later learned it is double, bends and can unwind-unzip • The standard for is called a B-form • It has 10.5 bp (base pairs)

9. Characteristics of DNA • 1. Accounts for all genetic variation between different individuals and organisms by the use of different: • a. Sequences of nitrogenous bases. • b. Lengths of DNA segments. • c. Numbers of chromosomes

10. Characteristics of DNA • 2. The amount of DNA in an organism DOES NOT relate to the size or complexity of the organism. • 3. DNA replication is the process through which cells copy DNA for transmission to daughter cells during cell division. • a. The double helix structure allows DNA to easily unzip down the center between nitrogenous bases. • b. Free floating nucleotides attach to each of the separated DNA strands forming 2 new strands of DNA, each an exact copy of the original.

11. Characteristics of DNA • 4. A mutation is an unexpected change in a DNA sequence, usually occurring during the replication / cell division. • a. Mutations are common in most organisms (especially simple organisms) though only a small percentage produce noticeable changes in organisms. • 5. DNA is passed to offspring during sexual reproduction through single chromosomes.

12. DNA and Genetics in Agricultural Biotechnology Objective 13.02: Explain the relationship between DNA, gene sequences, traits, and the genome.

13. Relationship between Genetic Terms • 1. Genetic hierarchy • a. A group of nucleotides = a gene / allele = 45-150 base pairs. • b. A group of genes = 1 strand of DNA. • c. Several condensed strands of DNA = 1 chromosome. • d. 2 chromosomes = 1 chromatid pair. • e. All possible gene forms in a population = Genome.

14. Relationship between Genetic Terms • 2. Mapping the genome of a species allows scientists to identify beneficial and harmful genes in a population, and is the first step in determining the location of specific genes on chromosomes. • a. Changes in the genome of a species occur slowly in response to environmental changes.

15. Relationship between Genetic Terms • 3. Polygenic traits are controlled by more genes and therefore it is more difficult to improve polygenic traits.

16. Human Genetics • 1. Almost all humans have 46 chromosomes. • a. Individuals with Down Syndrome have one extra chromosome. • 2. Humans generally differ from each other by approximately 3 million nitrogenous base pairs, or 0.1% of the total gene sequence.

17. DNA and Genetics in Agricultural Biotechnology Objective 13.03: Summarize the role of DNA in genetic disorders and mutations.

18. Basics of Genetic Disorders • 1. Definition- • diseases or other problems resulting from errors in the transmission of genetic information, or the expression of certain negative gene sequences. • 2. Most genetic disorders are recessive, and thus cannot be predicted without genetic analysis. • a. Recessive disorders are transmitted by carriers- parents with one dominant gene (normal) and one recessive gene (disorder). Ex- Tt • 3. Certain disorders are more common in certain populations. (The occurrence of sickle cell in African Americans.)

19. Mutations • 1. Definition- sudden unexpected changes in the genetic code of organism. Appear most often during the process of replication. • 2. Often result from increased levels of stress on cells just prior to or during cell division. • a. Stresses include - radiation, uv rays, environmental, etc.

20. Mutations • 3. Almost all mutated cells die immediately, or never impact living organisms. • a. Most mutations in organisms are harmful- ex: cancer. • b. A small fraction of noticeable mutations are beneficial, such as Chimeras which are used to give us variegated plants

21. Mutations • 4. Most mutations occur in developed plants and animals, affecting isolated groups of cells. Mutations are most devastating when they occur in the early development of organisms. (STEM CELL STAGE) • Types of mutations • a. Point mutation- a mutation that changes DNA at a single point, substituting one nucleotide pair. • b. Frameshift- nucleotides are inserted or deleted, altering the entire DNA sequence after the mutation.

22. Common Genetic Disorders • 1. Inherited Disorders • a. Ex: Tay- Sachs, Sickle Cell Anemia, Hemophilia, etc. • 2. Mutations • a. CANCER – uncontrolled division of abnormal cells. • b. Treatment must destroy mutated cells.

23. DNA and Genetics in Agricultural Biotechnology Objective 13.04: Outline the processes of mitosis and meiosis in plant and animal cells.

24. Mitosis • 1. Definition – • the process of cell division in all diploid cells. • a. Is constantly occurring in cells throughout plants and animals at all times (muscle cells, skin cells, stem cells, cambium cells).

25. Stages of Mitosis • a. Interphase - the period of cell growth and function prior to the beginning of true mitosis, in which the cells store energy for cellular division. • i) The cell replicates DNA and produces chromatid pairs. • ii) This is the longest period in the LIFE of a cell.

26. Stages of Mitosis • b. Prophase.- the first true stage of mitosis. • i) Nuclear membrane dissolves, centromeres form, and centrioles move towards opposite ends of the cell.

27. Stages of Mitosis • c. Metaphase.- the second and shortest stage of mitosis. • i) Chromatids align in the center of the cell and spindle fibers attach to centromeres from centrioles.

28. Stages of Mitosis • d. Anaphase.- the third stage of mitosis. • i) Chromatids are separated and pulled towards opposite ends of the cell by spindle fibers • ii) Errors in the transmission of genetic information are MOST LIKELY to occur at this stage.

29. Stages of Mitosis • e. Telephase.- the final and longest stage of mitosis. • i) Chromosomes reach opposite ends of the cell, and new nuclear membranes form for each new daughter cell.

30. Stages of Mitosis • f. Cytokinesis.- the actual division of daughter cells at the end of mitosis. • i) A cleavage furrow forms pinching apart cells in animals. • ii) In plant cells, a cell plate forms between daughter cells, dividing cells and forming the new section of the cell wall.

31. Meiosis • 1. Definition- the specialized form of cell division that occurs ONLY IN HAPLOID CELLS. (sperm, pollen, eggs, ovums) • a. Very similar in process to mitosis, except with two cycles, producing 4 haploid daughter cells (23 chromosomes each) • b. Production of male sex cells = spermatogenesis – producing 4 sperm • c. Production of female sex cells = oogenesis – usually produces 1 viable egg - other 3 abort.

32. Stages of Meiosis • a. Interphase - same as mitosis- period of growth and function

33. Stages of Meiosis • b. Meiosis I : • prophase I, metaphase I, anaphase I, telephaseIcytokinesis • i) Reduction process- changes cell from diploid to haploid.

34. Stages of Meiosis • c. Meiosis II: • prophase II, metaphase II, anaphase II, telephase II, cytokinesis/Prophase II is responsible for aligning chromosomes for the final division. • i) Division process- creates 2 distinct haploid cells.

35. Stages of Meiosis • 3. The stages of Meiosis I & Meiosis II are identical to the stages of Mitosis, • but with different cells for a different purpose.