Karyotype Activity.doc.docx



RETURN THIS PACKET AT THE END OF CLASS! TRISOMY is the presence of three instead of the normal pair of two homologous chromosomes for a particular chromosome number which gives the organism an extra chromosome in each cell.3838575149225Examples of Trisomy:Patau Syndrome – Trisomy 13 – is a genetic disorder caused by the presence of an extra 13th chromosome. It is rare for fetuses with this condition to be born, so it occurs in only 1 in 25,000 live births. If a child is born with this Patau Syndrome, it is rare that they will live very long with 45% dying within the first month and 90% by six months. Less than 5% reach of individuals with Patau syndrome will reach 3 years old. The extra chromosome 13 disrupts the normal course of development, causing heart and kidney defects and severely abnormal brain functions which virtually always leads to death in early infancy. This baby has very pronounced clefts of the lip and palate, a broad nose, a small cranium, polydactyl (extra fingers and toes), deafness, and nonfunctional eyes. Trisomy 16 – is a chromosomal disorder in which an individual has three copies of chromosome 16 instead of the usual two. A fetus with an extra chromosome 16 will not survive past the first trimester of pregnancy. It is not possible for a child to be born with an extra copy of chromosome 16. Trisomy 16 is not compatible with life and is the most common chromosomal cause of miscarriages (causing over 100,000 pregnancy losses a year, representing almost 10% of miscarriage in the U.S.).Edwards Syndrome – Trisomy 18 – is the genetic disease caused by an extra 18th chromosome. It is the second most common autosomal Trisomy, after Down Syndrome, that lives through birth. The incidence of Edwards syndrome is estimated at 1 in 3,000 live births. The incidence increases as the mother’s age increases. The syndrome has a very low rate of survival with only 70% of these children surviving one month and only 10% survive one year. Nearly all babies born with this condition die in early infancy due to heart abnormalities, kidney malformation, and other internal organ disorders. Physical characteristics of this disorder include an elongated skull, a very narrow pelvis, rocker bottom feet, and underdeveloped thumbs and or nails. In addition, the ears are often low set and the mouth and teeth are small. Down Syndrome – Trisomy 21 – is a genetic disorder caused by the presence of an extra 21st chromosome. Individuals with Down syndrome are more likely to survive through birth and beyond as compared to other trisomy disorders. With advanced medical treatments, the average life span of an individual with Down syndrome is now about 50 years. This is one of the most common causes of mental deficiencies. The child can have an IQ between 25-74 whereas an average person has an IQ between 90-110. There are also a number of characteristic features in Down syndrome individuals. They are usually short, have broad hands, stubby fingers and toes, a wide round face, and a large protruding tongue that makes speech difficult. Individuals with this syndrome have a high occurrence of respiratory infections, heart defects, and leukemia. The average risk of having a child with trisomy 21 is 1/750 live births. This disorder is more likely to occur as the mother’s age increases. Mothers in their early twenties have a risk of 1/1,500 and women over 35 have a risk factor of 1/70, which jumps top 1/25 for women 45 and over. Objectives – In this activity you will:Construct and analyze a karyotype.Identify homologous chromosome pairs by their length, centromere position, and banding pattern.Determine the gender of an individual from a karyotype and determine if a chromosomal abnormality is present.MaterialsChromosome spreadScissorsTransparent tape or glueBackground InformationA genetic disorder is a condition caused by abnormalities in genes or chromosomes. Some diseases, such as cancer, are due to genetic abnormalities acquired in a few cells during a person’s life. However, the term “genetic disease/disorder” most commonly refers to diseases present in all cells of the body and present since fertilization. Some genetic disorders are caused by chromosomal abnormalities due to errors in cell division. Currently around 4,000 genetic disorders are known, with more being discovered. Most disorders are quite rare and affect one person in every several thousands or millions. There are several genetic disorders that involve entire chromosomes. A change in the number of chromosomes that can lead to a genetic disorder is called aneuploidy.One way of studying genetic disorders is to observe the chromosomes themselves. In order to do this, cells from a person are grown in a laboratory. After the cells have reproduced a few times, they are treated with a chemical that stops cell division at the metaphase stage. During metaphase, the chromosomes are at the best length for identification. 463867571120The cells are treated further, stained, and then placed on glass slides. The chromosomes are observed under the microscope where they are counted, checked for abnormalities, and photographed. The photograph is then enlarged, and the chromosomes are individually cut out. The chromosomes are identified and arranged in homologous pairs according to their length, the position of their centromeres, and their banding patterns. The arrangement of homologous pairs of chromosomes from largest to smallest is called a karyotype. A karyotype can be analyzed to determine the gender of the individual and whether there are any chromosomal abnormalities. Pretend that you are a medical lab technician. One of your jobs is to assist with prenatal testing. Currently, you are working on the case of Mr. and Mrs. Smith. Mrs. Smith is pregnant, and her doctor has recommended a type of prenatal testing called amniocentesis. During amniocentesis, a sample of the amniotic fluid that surrounds the baby is removed from the mother. This fluid contains the unborn baby’s cells. You have been given a photograph of the chromosomes in the unborn baby’s cells, which were obtained through amniocentesis. Your job is to complete and analyze a karyotype of these chromosomes to determine the gender of the Smith’s baby and whether the baby is normal or has a genetic disorder. ProcedureCarefully cut out each chromosome from the chromosome spread. Be sure to leave a slight margin around each chromosome. Do not lose any chromosome pieces!Arrange the chromosomes in homologous pairs. Arrange the pairs according to their length, from largest (#1) to smallest (#22). Tape or glue each homologous pair to the Human Karyotype Form. Place the pairs in order, starting with the longest pair at position 1, the shortest pair at position 22, and the sex chromosomes at the end.The diagram you have made is a karyotype. Analyze the karyotype and answer the conclusion questions.Throw away any paper scraps in the garbage and return the items you have borrowed.Name _________________________________ Karyotype Conclusion & Analysis QuestionsWhat is a karyotype and what are they used for? How is a karyotype made for an unborn baby? Explain why a karyotype cannot be made from cells that are in interphase.Why might a laboratory worker attempting to diagnose a genetic disorder prefer to work with photographs of chromosomes rather than the chromosomes themselves?What does aneuploidy mean? How are karyotypes used to check for these conditions?Examine your karyotype. How many total chromosomes does this baby have? ________________How many sex chromosomes are present? ____________ How many autosomes (chromosomes that are not the sex chromosomes)? _____________Explain how you matched up the homologous chromosomes. What process did you go through?Is the baby male or female? How do you know?The human male determines the gender of his offspring. Explain this statement.Will the baby have a genetic disorder? How do you know? If applicable, name the genetic disorder and describe what the characteristics are of the condition.Make a prediction: Meiosis is the process of cell division that cells go through in order to form the gametes (egg and sperm). During this process, we start with one cell and it undergoes 2 divisions. The end result is 4 gametes that each have half of the chromosomes that the original cell had (each has 23 unpaired chromosomes). This is important because then when the egg and sperm unite, then the new organism that is created will have a complete set of chromosomes. However, we can see that sometimes people end up with too many or too few chromosomes. How do you think that happens? ................
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