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The picture was taken from the slide prepared during practical class. These condensed chromosomes observed were stained using a Cytogenetics technique called Giemsa banding that reveal structural features of the chromosomes ; the figure above shows different types of chromosome. Point (A) as shown on the figure represent the longest chromosomes observed on the metaphase spread, (B) represent the metacentric chromosome, (C) Submetacentric chromosome and (D) is the acrocentric chromosome. The chromosome were observed at 100X magnification
Fig 2: longest chromosome
Centromere in the middle of chromosome holding two sisters chromatids together is represented in the above figure (2), the p arm is the shortest and the q arm is the longest arm also are visible. Telomeres are located in the end caps and protect the chromosomes against homologous and non-homologous recombination.
Question 2: Draw an acrocentric, metacentric and submetacentric chromosome including the G-banding pattern. (1 points)
Fig : 3 chromosome structure and G- banding pattern
(C) Chromosome acocentric
(B) Chromosome submetacentric
(A) Chromosome metacentric
The above figure (2) was drawn by me. Letter A represent the metacentric chromosome where the centromere is placed in the middle of chromosomes into two arms with approximately equal length. B is the submetacentric chromosomes in which the centromere is a little away from the center and therefore chromatid of one side are slightly longer than the other chromatid. The last type of chromosome represented in this picture is called acrocentric as the centromere is d closer to one side of the chromatid leaving the chromatid on the opposite side is very longer than the other side.
Question 3: Count the average number of chromosomes in 10 cells - show your workings. (1point)
Fig 4:The average number of chromosomes in the cells
Chromosomes in metaphase spread
This figure shows Tree quarter of the field of view observed in the microscope. The number of the chromosomes was counted in pair as a diploid organism is comprised of 2 copies of every chromosome. To count the number of these chromosomes is also depending from the species to species . In fact the human nucleus comprises of 22 pair of autosomal, and 2 pair of sex chromosomes. Particularly 82 number of chromosomes were approximately counted from each metaphase spread observe in this field of view containing Hela cells. So in total 210 chromosomes were observed in the field of view. This particular image as observed at 40 X magnification
Question 4: Why is Giemsa band staining of chromosomes used in cytogenetics laboratories? (1 point)
Condensed chromosome during metaphase spread could be stained with Giesma banding which is a useful analytical method in Cytogenetics to generate a visible karyotype. Routine G banding with trypsin in Cytogenetics is useful as it gives each chromosome a distinctive banded pattern that enable a clear identification of isolate or discrete regions all along each chromosome and the opportunity to examine for chromosomal imbalance by standard microscopic. In the clinical setting, the technique is useful to assess for any chromosomal imbalance in a wide range of patients.
Question 5: Describe the disease that the patient whose cells were used to make the cell line had. (2 point)
The Hela cells taken from Henritta Lack tumor had cancer. She suffered from cervical cancer. Cervical cancer is the most common types of cancer that affect women's reproductive organs. This cancer originates in the lower, narrow part of the uterus. The disease is characterized by malignant neoplasms ( the aberrant growth) from cervical cells. Most cervical cancers arise in the squamous epithelial cells lining the cervix. It has been proven that the Human Papilloma virus (HPV) is the cause of the majority of different type of cervical cancers as all Hela cells contain HPV.
Question 6: During which stage of mitosis is the chromosomes in their most condensed state and best for karyotyping? (1 point)
Methaphase is the best stage of cell division ( mitosis) where Chromosomes can be easily seen with a light microscope in their condensed form observed at 1000 x to carry out the karyotyping.
Question 7: Name two sources of cells typically used for karyotyping in a hospital-based Cytogenetics laboratory. Explain why these types of cells are used. (1 point)
Normally, in the hospital -based Cytogenetics laboratory, the two sources of cells used for Karyotyping are peripheral blood lymphocyte cells and fetal skin cells originated from the placenta or amniotic fluid. Lymphocyte cells are good sources as they can promptly proliferate and provide a very accessible source of metaphase cells that is useful for Cytogenetics. Amniotic fluid cells are also appropriate for karyotyping as these cells can be easily grown in tissue culture for chromosome analysis. For instance, down syndrome which is genetics defects condition can be detected by karyotyping method from the cells obtain from the amniotic fluid.
Question 8: Imagine you are soon to be a new parent. The doctor has explained to you the results of your amniocentesis test. Your 15-week old foetus has Down's Syndrome caused by an abnormal number of chromosomes.
How is an amniocentesis test performed? (1 point)
Amniocentesis is the most common prenatal test used to diagnose chromosomal and genetic birth defects by routine cytogenetic analysis. During the procedure, an ultrasound image is used as a guide. With the syringe, a small sample of amniotic fluid is removed from the amniotic sac surrounded the fetus and send to the laboratory for analysis. The fluid contains all the genetic make of the unborn baby.
Describe the karyotype that typifies a Down's Syndrome child. (0.5 points)
The karyotype of a child contains a three chromosomes in the 21st position, where there should only be two.
Draw the affected chromosome after G-banding. (1 point)
Fig 6: The affected chromosome with Down syndrome after G-banding
Extra abnormal chromosome
Normal Chromosome 21
Normal Chromosome 21
G-Banded karyotype of chromosome 21. On the right, is shown the 2 pairs normal chromosomes 21; on the right, an additional chromosome added making 3 copies of chromosomes (trisomy)
What are the typical symptoms your child will have? (2 points)
Down syndrome symptoms differ from child to child and can range from benign to malignant. Children with Down syndrome have some distinctive recognized physical appearance. They have craniofacial features which can include an anterior and posterior flattened head. Their round faces with shaped eyes as a result of epicanthal folds, dysplastic low set of ears, small and flat nose; most of these children have smaller head than normal head shape. In addition, their mouth is small with a protruding tongue and dental abnormalities as well as short and broad neck. Besides their facial and physical appearance, children affected with Down syndrome are at higher risk of developing many medical conditions. Research suggests that the majority of children with Down syndrome have a condition called hypotonia which is characterized by low muscle tone. Meaning that their muscles appear floppy therefore are weak. Their Motricity is compromised due to their Hypotonicity (Hecht and Hook,1994).
Which diseases are your child more likely to develop and at what age? (1 point)
The extra chromosome 21 that cause Down syndrome in children affects almost every organ system in the body and has a devastating consequences phenotypically, as well as life-threatening conditions. About half of children with Down syndrome are born with congenital heart defects Freeman et al., (2008). As the immune system of children affected by Down syndrome are compromised and also as they are exposed to autoimmune disease, they are being much more susceptible to infectious diseases, such as pneumonia or hypothyroidism. Obstructive sleep apnea is also one of the condition that these children suffer, as there are soft and their skeleton is altered resulting in the airway obstruction. Children with Down syndrome are at greater risk of developing leukemia than normal children. This condition affected children in delaying their physical growth, their maturation, the development of their bone, and their dental eruption. Children with trisomy have decreased buffering of metabolic reactions that lead to to hyperuricemia and increased insulin resistance.diabetes mellitus is common among them
The exact age that that most of the disease occurs cannot be determined as it subject of the individual.
What is the prognosis for your child? (2 points)
The prognosis for a child with Down syndrome depends with the underlying medical and developmental conditions. Most of the health problems related with trisomy can be treated effectively. The life expectancy for people with Down syndrome are now double to 55 years since 1983.
Abnormalities in chromosome number are detrimental and usually lethal. Speculate as to why this is not the case in Down's Syndrome. (1 point)
Down syndrome is the most common genetic disorder that affects human chromosome but it is not lethal as others chromosomal condition. There is a range of variation in the phenotype of the disease also even thought there is not a cure for the condition, medical treatment to lessen the symptoms of this disease is well known and proven to be effective.