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Patterns In Chromosomal Inheritance Changes in Chromosome Number Karyotype Recall from MITOSIS, DNA replication during interphase Single stranded Become visible double stranded Cell is lysed (physically disrupted) Chromosomes are photographed Images are cut out and arranged by shape and size in an orderly arrangement – a KARYOTYPE. Karyotype (cont’d) In most higher plants and animals, including humans, chromosomes from the body cells can be matched up in pairs. These are the HOMOLOGOUS chromosomes. Karyotype (cont’d) Homologues look alike. Same length Centromeres are in the same position Same pattern of light and dark bands when stained Genes for the same inherited characteristics are carried in the same order. Karyotype (unsorted microscopic image) http://www.unm.edu/~vscience/images/HeLa%20Karyotype%203%20(1000x).jpg Karyotype (unsorted enhanced image) http://www.contexo.info/DNA_Basics/chromosomes.htm Karyotype (sorted image) MALE FEMALE http://www.contexo.info/DNA_Basics/chromosomes.htm Karyotype (cont’d) Reveal chromosomal abnormalities Missing homologue (monosomy) Extra homologue (trisomy) Failed crossover resulting in a shortened homologue Lengthened homologue. Such disorders often result in syndromes a group of symptoms that are always occurring together. Producing a Karyotype 1. Any cell in the body can be a source of chromosomes. Usually, white blood cells are used in children or adults. (RBC – no nucleus) In fetus, cells can be obtained by either amniocentesis or chorionic villi sampling. Another development in testing is non-invasive – It is plasma testing – It is not definitive but results in probability statistics. Amniocentesis Amniotic fluid from the uterus of pregnant woman is obtained with a large needle ultrasound helps locate the baby and also to guide the needle to the best location. http://www.nebraskamed.com/manageHealth/libraries/Defa ult.aspx?P=1241 Amniocentesis Initial blood tests are done to determine when if the procedure should be done. It is done at the 14th-17th week of pregnancy. Amniotic fluid contains fetal cells which are then cultured to increase their numbers takes about 4 wks. http://fig.cox.miami.edu/Faculty/Dana/amniocentesis.jpg Amniocentesis As many as 400 chromosomal and biochemical problems can be detected with the cells in the amniotic fluid Risk of spontaneous abortion increases by 0.3% due to the procedure. "Human Atlas: Amniocentesis" Chorionic Villus Sampling Chorionic cells in the region where the placenta develops are taken Done as early as the 5th – 12th week of pregnancy A long thin tube is inserted into the uterus with the help of ultrasound. http://www.uptodate.com/patients/content/image.do?imag eKey=OBGYN%2F15838 Chorionic Villus Sampling Karyotyping is done immediately—results are disclosed at an earlier date. Greater risk of spontaneous abortion (0.8%). Since no amniotic fluid is present, no biochemical test results are possible Chorionic Villus Sampling Video Cell Staining & Imaging 2. 3. 4. After either amniocentesis or chorionic villi sampling, the obtained cells are stimulated to divide by mitosis. A chemical is used to stop mitosis at the point the chromosomes are most condensed and visible. Cells are killed and spread on a microscope slide and dried. Stains are applied to the slides to make the banding on the chromosomes more visible. This makes chromosome pairing easier. Today, computer photography and programs arrange the chromosomes in their homologous pairs. Cell Staining & Imaging