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Practical Genetics By dr. Rehab Mamdouh 1 Blood grouping 1. The differences in human blood are due to the presence or absence of certain protein molecules called antigens and antibodies. 2. The antigens are located on the surface of the red blood cells and the antibodies are in the blood plasma. Individuals have different types and combinations of these molecules. Significance of the blood grouping: For a blood transfusion to be successful blood groups must be compatible between the donor blood and the patient blood. If they are not, the red blood cells from the donated blood will clump or agglutinate. The agglutinated red cells can clog blood vessels and stop the circulation of the blood to various parts of the body. The agglutinated red blood cells also crack and its contents leak out in the body. The red blood cells contain hemoglobin which becomes toxic when outside the cell. This can have fatal consequences for the patient. What are the different blood groups? There are more than 20 genetically determined blood group systems known, but the AB0 and Rh systems are the most important ones used for blood transfusions. (A) AB0 blood grouping system: According to the AB0 blood group system there are four different kinds of blood groups: 1. Blood group A: If you belong to the blood group A, you have A antigens on the surface of your red blood cells and B antibodies in your blood plasma. 2. Blood group B: If you belong to the blood group B, you have B antigens on the surface of your red blood cells and A antibodies in your blood plasma. 3. Blood group AB: If you belong to the blood group AB, you have both A and B antigens on the surface of your red blood cells and no A or B antibodies at all in your blood plasma. 4. Blood group 0: 2 If you belong to the blood group 0 (null), you have neither A or B antigens on the surface of your red blood cells but you have both A and B antibodies in your blood plasma (B) Rh (Rhesus) factor blood grouping system: 1. Rh+ Many people also have a so called Rh factor on the red blood cell's surface. This is also an antigen and those who have it are called Rh.+ 2. RhThose who haven't Rh factor on the red blood cell's surface are called Rh-. 3 4 Observing Mitosis with Fluorescence Microscopy in onion root tips Showing different stages (prophase, Metaphase, anaphase, telophase and cytokinesis Comment: Mitosis is the mechanism that allows the nuclei of cells to split and provide each daughter cell with a complete set of chromosomes during cellular division. This, coupled with cytokinesis (division of the cytoplasm), occurs in all multicellular plants and animals to permit growth of the organism. Interphase was Observed with Fluorescence Microscopy in onion root tips Division type: Mitosis Comment normal resting cell exists in a state called interphase in which the chromatin is undifferentiated in the heavily-stained nucleus, as illustrated above. Before the cell enters the mitosis phase, it first undergoes a synthesis or S phase where each chromosome is duplicated and consists of two sister chromatids joined together by a specific DNA sequence known as a centromere. 5 Early prophase was Observed with Fluorescence Microscopy in onion root tips Division type: Mitosis Comment The first phase of mitosis is known as the prophase, where the nuclear chromatin starts to become organized and condenses into thick strands that eventually become chromosomes. During prophase, the cytoskeleton (composed of cytoplasmic microtubules) begins to disassemble and the main component of the mitotic apparatus, the mitotic spindle begins to form outside the nucleus at opposite ends of the cell. The photomicrograph below depicts the initial chromosome condensation at the beginning of prophase (early prophase) when the nucleolus is still intact. 6 Late prophase was Observed with Fluorescence Microscopy in onion root tips Division type: Mitosis Comment Late prophase begins with the disruption of the nuclear envelope, which is broken down into small membrane vesicles that closely resemble the endoplasmic reticulum and tend to remain visible around the mitotic spindle. During this period the chromosomes continue to condense and gradually shorten and thicken until they have completely formed the units that will undergo mitosis. The nucleolus also disappears during this period. The mitotic spindle microtubules are now free to enter the nuclear region, and formation of specialized protein complexes called kinetochores begins on each centromere. These complexes become attached to some of the spindle microtubules, which are then termed kinetochore microtubules. Other microtubules in the spindle (not attached to centromeres) are termed polar microtubules and these help form and maintain the spindle structure along with astral microtubules, which remain outside the spindle. 7 Metaphase was Observed with Fluorescence Microscopy in onion root tips Division type: Mitosis Comment The current phase is called metaphase where the chromosomes, attached to the kinetochore microtubules, begin to align in one plane (the metaphase plate) halfway between the spindle poles. The kinetochore microtubules exert tension on the chromosomes and the entire spindle-chromosome complex is now ready for the next event. 8 Early Anaphase was Observed with Fluorescence Microscopy in onion root tips Division type: Mitosis Comment Almost immediately after the metaphase chromosomes are aligned at the metaphase plate, the two halves of each chromosome are pulled apart by the spindle apparatus and migrate to the opposite spindle poles. The kinetochore microtubules shorten as the chromosomes are pulled toward the poles, while the polar microtubules elongate to assist in the separation. The photomicrograph below illustrates the early stage of anaphase where the chromosomes are just becoming completely separated. The microtubules are clearly visible in this complex. q 9 Late Anaphase was Observed with Fluorescence Microscopy in onion root tips Division type: Mitosis Comment Anaphase typically is a rapid process that lasts only a few minutes. When the chromosomes have completely migrated to the spindle poles, the kinetochore microtubules begin to disappear, although the polar microtubules continue to elongate. 11 Telophase was Observed with Fluorescence Microscopy in onion root tips Division type: Mitosis Comment chromosomes and their extrusion to the spindle poles, the nuclear membrane begins to reform around each group of chromosomes at the opposite ends of the cell. The nucleoli also reappear in what will eventually become the two new cell nuclei. The photomicrograph below captures a cell in late telophase where the new membrane is beginning to divide the cell but the nuclei have not completely reformed and cytokinesis has not yet finished. 11 Cytokinesis was Observed with Fluorescence Microscopy in onion root tips Division type: Mitosis Comment When telophase is complete and the new cell membrane (or wall in the case of the onion root tips) is being formed, the nuclei have almost matured to the pre-mitotic state. The final steps are completion of the total formation of a membrane between each of the new daughter cells to yield two separate new cells. 12 Give the crossing probability for first and second generation of two traits between purpled flower's plant which has tall stem. You should Know these traits are dominant. d TRUEBREEDING purple white flowers, tall flowers, dwarf PARENTS: AABB GAMETES: AB x AB ab F1 HYBRID AaBb OFFSPRING: All purple-flowered, tall 16 Allele Combinations in F2 9: purple flowers and tall 3: purple flowers and dwarf 3: white flowers and tall 1 white flowers and dwarf 13 aabb ab gametes AB Ab aB ab AB AABB AABb AaBB AaBb Ab AABb AAbb AaBb Aabb aB AaBB aABb aaBB aaBb ab AaBb Aabb aaBb aabb Give an example for incomplete dominance? e.g: Flower Color in Snapdragons Red-flowered plant X (homozygote) White-flowered plant (homozygote) Pink-flowered F1 plants Heterozygotes Pink-flowered plant X Pink-flowered plant White-, pink-, and red-flowered plants in a 1:2:1 ratio 14