GENETICS LABORATORY EXERCISE 1-7 Exercise 1 Phenotypic Variation in Organisms Variation Basic quality of living things What proves the identity of the individual species (different from other types of organisms) Maintains the characteristics that relate it with others of its own kind (same species) Variation can come in different types of forms 1. Physiological variation a. Albinism: Inability to produce melanin b. Diabetes: Deficiency of insulin 2. Morphological variation Different shapes (round or oval), texture (smooth or wrinkled), color patterns (plain to bent lines or mosaics), eye (red eye or white eye) 3. Behavioral variation Migration or nesting habits of birds - There is also variations attributed to distinguish sexuality
Phenotype Expressed traits of the genotype reflected on the organism
Physical expression of the trait or characteristic
Genotype Alleles: different variations of a gene and assemble in a loci or gene Alleles determine the genotype of the species
Exercise 2 Physical Basis of Heredity Cell The basic structural and physiological unit of the body of an organism Prokaryotic and Eukaryotic cells carry genetic information in their chromosomes Cells undergo cell division: Chromosomes replicate and produce daughter cells Cell cycle: Chromosomes grow and reproduce – metabolic activities are regular and repetitive
Cell Cycle Interphase
MPF CdK and cyclins which triggers progression throughout the cell P53 Partakes in apopstosis Functions to block cell cycle Cell Division Mitosis - New cells are generate - Produces Diploid organisms (same as the parent cells)
The cell cycle is 16 hours Mitosis happens for 1 hour Interphase is a non-mitotic portion of the cell cycle Gap 0 Gap 1 Synthesis DNA replication occurs Gap 2 Mitosis Chromosomes start to separate Cytokinesis starts to occur (division of the cytoplasm) - The cell cycle has 3 checkpoints for regulation (G1, G2 and M) - Non-dividing cells go to the G0 phase CDK Cylin dependent kinase Major control switches of the cell which causes the movement from G1 to S to G2 to M
Prophase Chromosomes condense and become visible Centrioles form and move towards opposite poles Nuclear membrane dissolves Mitotic spindle forms Spindle fibers attach to each sister chromatid at the kinetochore spindle fibers are microtubules made up of tubulin Metaphase Centrioles have fully migrated to opposite poles Chromosomes line up at the “metaphase plate” “equatorial plate” Anaphase Spindles attached to kinetochores are shorten (pulled) Sister chromatids are pulled apart and chromatids are at the opposite poles Telophase Chromosomes decondense Nuclear envelop is formed
Cytokinesis (division of the cytoplasm) is completed Formation of 2 daughter cells - plants do not have cytokinesis because It has a cell wall
Meiosis - Formation of gametes, generated for reproduction (production of haploid cells) - Chromosome number in daughter cells is reduced to half Important events: 1. Crossing over between homologous chromosomes at prophase I 2. Independent assortment of homologous pairs at metaphase I Meiosis I Prophase I Chromosomes condense and become visible Centrioles move to opposite poles Nuclear membrane starts to dissolve Formation of Tetrad (4 chromatids): Homologs pair up and begins to dissolve Crossing over: Homologous chromosomes swap genetic material Metaphase I Microtubules grow from the centrioles and attach to the centromeres Tetrads are lined up along the metaphase plate or the cell equator Anaphase I Centromeres break and homologous chromosomes separate (sister chromatids are still attached) Cytokinesis begins
Telophase I Cytokinesis is producing two daughter cells
complete haploid
Meiosis II Prophase II Centrioles form and move towards opposite poles Nuclear membrane dissolves Metaphase II Microtubules grow from the centrioles and attach to the centromeres Sister chromatids line up along the cell equator Anaphase II Sister chromatids separate Cytokinesis begins (Division of the cytoplasm) Telophase II Chromosomes decondense Formation of four haploid daughter cells 1. Allium Cepa Chromosome number 2n: 16 2. Whitefish Blastula - Used to study MITOSIS - Chromosomes are actively dividing Chromosome number 2n: 80 2. Grasshopper Testis Chromosome number 2n: 24 Prophase I Leptotene Chromosomes are finely beaded filaments Chromatin is filamentous Chromosomes are uncoiled
Pachytene Chromosomes shorten and become thicker Complete pairing and exchange of chromosomal arms Haploid condition Diplotene Chromosomes are partly split Chiasma Diakinesis Coiling of chromosomes Chromosomes are at its shortes and thickets Terminalization of one or more chiasmata
Involves one type of parent – a diploid or 2N individual which produces gametes through gametic meiosis
Haplodiplobiontic, diploid-haploid (H. d-h)
Haplobiontic, haploid (H,h)
Involves one type of parent – a haploid which produces gametes through mitosis
Involves two types of parents – one stage is diploid (diploid sporophyte stage), producing spores through meiosis. The haploid spores germinate into a gametophyte (N) that produces gametes through mitosis
Life cycle 1. Agaricuss (Mushroom) 2. Zea Mays (Corn)
Exercise 4 Karyotyping Method that is used in determining the number, shapes, and sizes of chromosome set of organisms Somatic cells undergoing metaphase of mitosis best exhibit chromosomes for this purpose Chromosomes Compact and composed of two identical threads Double nature of chromosomes extends along its length except at the region of the centromere which may be at the middle, off- center, close to one end or at the terminal end
3. Drosophila (Fruit fly)
Melanogaster
Human karyotype Correct number of human chromosomes: 46 (23 pairs) White blood cells were used to karyotype Method used for karyotyping human chromosomes: 1. Subject the cultured human blood cells to a mitotic stimulator 2. White blood cells under mitosis and then trapped in metaphase by colchicine 3. Cells swell and nuclear membranes rapture and chromosomes scatter Y chromosome is shorter than X chromosome Diseases 1. Trisonomy Syndrome 2. Klinefelter’s Syndrome
Exercise 5 Care and Culture of Drosophila Melanogaster
Why is a fruit fly used? 1. Short life cycle 2. Produces a fairly large number of offspring 3. Easy to grow and maintain in the laboratory using a variety of simple culture media 4. Convenient to handle and store due to small size 5. Possess only 4 pairs of chromosomes making analysis of crosses easy 6. Great variability of inherited characteristics 7. Availability of literatures Fruit fly has 8 chromosomes (4 pairs) Trapping Make use of banana peels or any dry fruit Banana peels or any dry fruit is used as a bait for the fruit flies Culturing Mashed banana (Food medium for the drosophila) Propionic acid or yeast (OPTIONAL) Subculturing This is done when there are many flies in one culture bottle CONGESTION may be a factor which can cause the deaths of the flies
Unregulated gene action may result unusually to unusual gene behavior Repeated replication ovvurs while in synopsis of homologue which produces polytene or poly-
stranded giant chromosomes Polytene chromosomes aare viewed as enlarged chromatin puffs which are long looped structures of DNA
Histochemical techniques Use third instar larva Acetocarmine/Acetoorcinol - This dye is used to stain the DNA (DNA specific stain)
