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What is a Karyotype? Karyotype: picture of an individual’s chromosomes arranged in homologous pairs. Chromosomes are usually extracted during METAPHASE of a cell. Why? You can form a karyotype from any cell that is going through metaphase. You can identify the gender of the person by looking at the sex chromosomes on the karyotype. XX Female XY Male Doctors can also run tests on fetuses to check for chromosomal errors. This test is called an amniocentesis. What happens when things go wrong with the chromosomes? Nondisjunction When homologous chromosomes or sister chromatids fail to separate during meiosis. -Can occur in anaphase I or II; Resulting in gametes with abnormal # of chromosomes. It is not fully understood why nondisjunction occurs. *usually occurs in women over 40 Nondisjunction • Example of nondisjunction: Trisomy-21 an error most likely during meiosis I, causing 3 of the 21st chromosome. Commonly known as: Down’s Syndrome Symptoms: characteristic facial features, below average height, heart defects, impaired immune system, varying degrees of mental disability. Other forms of Nondisjunction Trisomy-13: (Patau Syndrome) Due to an extra chromosome on The 13th chromosome. 1 in 10,000 of children born. There are varying degrees. Symptoms: cleft lip, clenched fist, close set eyes, mental Retardation, etc. More than 80% die in the first year. Klinefelter’s Syndrome: (XXY Male) When a male has an extra X chromosome in most of their cells. Most common symptom is infertility. Most do not know they have it until puberty. Have less testosterone, so lack some male features. **caused by nondisjunction Turner Syndrome: (Monosomy-X) Found in females that do not have the normal XX in their cells. They only have one. 1 in 2000 live births. Symptoms: swollen hands and feet, lack female features after puberty, wide, webbed neck, flat/broad chest, drooping eyes, infertility. Damaged Chromosomes Chromosomes can also be damaged and cause problems. There are 4 types of changes that can occur to chromosomes and cause varying problems to the body. Duplication: when part of the chromosome is repeated. Not always fatal but can cause some developmental abnormalities. Deletion: when part of the chromosome is lost. Inversion: reversing a section of the original chromosome. (not as harmful) Translocation: when a section of one chromosome attaches to a NONhomologous chromosome. Jumping GENES Transposons: where a section/gene of a chromosome “jumps” to another chromosome. Disrupting the genes. Barbara McClintock discovered these in the 1940s with variations of corn. She received the Nobel Prize in 1983 for her pioneering work!