What is the name of the genetic disorder caused by the presence of an extra chromosome 21?
A. Turner syndrome
B. Klinefelter syndrome
C. Down syndrome
D. Huntington's disease
Down syndrome is a genetic disorder caused by the presence of an extra copy of chromosome 21. It is also known as trisomy 21, because affected individuals have three copies of chromosome 21 instead of the normal two.
The extra chromosome 21 in Down syndrome occurs due to a random error in cell division, which leads to the production of an abnormal gamete (egg or sperm) with an extra copy of the chromosome. When this gamete fuses with a normal gamete during fertilization, the resulting zygote has 47 chromosomes instead of the usual 46, and develops into a fetus with Down syndrome.
Down syndrome is characterized by a range of physical and intellectual symptoms, including developmental delays, intellectual disability, distinctive facial features, heart defects, and increased risk of certain medical conditions such as leukemia and Alzheimer's disease. However, the severity and expression of these symptoms can vary widely among affected individuals.
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Therefore, the Correct Answer is C.
More Questions on TEAS 7 Science
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Q #1: Which of the following units is used to indicate length?
A. kg
B. l
C. s
D. m
Answer Explanation
The unit used to indicate length is the meter (m). It is the base unit of length in the Internaonal System of Units (SI).
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Q #2: During embryonic development, which of the following germ layers forms the nervous system?
A. Ectoderm
B. Endoderm
C. Mesoderm
D. Exoderm
Answer Explanation
The three germ layers that form during embryonic development are the ectoderm, mesoderm, and endoderm. The ectoderm is the outermost layer, and it gives rise to the skin, hair, nails, and nervous system. The nervous system develops from a specialized region of the ectoderm called the neural plate, which invaginates to form the neural tube. The neural tube ulmately gives rise to the brain and spinal cord, which make up the central nervous system, as well as the peripheral nervous system. The endoderm gives rise to the lining of the digesve and respiratory tracts, while the mesoderm gives rise to the musculoskeletal system, circulatory system, and several other organs. The exoderm is not a germ layer and does not exist during embryonic development.
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Q #3: Which of the following substances is excreted by the kidneys to regulate blood pressure?
A. renin
B. erythropoien
C. calcitriol
D. urobilinogen
Answer Explanation
The kidneys secrete a number of hormones, which are important for normal functioning of the body.
If blood pressure falls, renin is secreted by the kidneys to constrict the small blood vessels, thereby increasing blood pressure. If the kidneys aren’t functioning correctly, too much renin can be produced, increasing blood pressure and sometimes resulting in hypertension (high blood pressure). This is why a number of people with kidney diseases also have high blood pressure.
