Unit A Reproduction

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4.5 CHECK YOUR Understanding 1. How many pairs of homologous chromosomes are in a single human body cell? 2. What is nondisjunction? 3. Explain how a human somatic cell could have 47 chromosomes. 4. A zygote contains 45 chromosomes. How many chromosomes would be found in the muscle cells of the baby? 5. Use Figure 4 to answer the following questions. (a) Which cells in the diagram have the normal diploid chromosome number? (b) How many chromosomes would be found in cell A? (c) How many chromosomes would be found in cell B? 6 6 nondisjunction normal meiosis fertilization normal meiosis A B 3 3 3 3 3 3 8. (a) Which gender are people with Turner syndrome? (b) Describe the sex chromosomes of someone with Turner syndrome. 9. Match the individuals in Table 1 to the correct chromosome makeup. (The number represents the number of non-sex chromosomes.) Table 1 Individual Chromosome makeup a) normal male 44XX b) normal female 45XX c) Klinefelter syndrome male 45XY d) Down syndrome female 44XY e) Turner syndrome female 44X f) Down syndrome male 44XXY 10. Both Down syndrome and Klinefelter syndrome somatic cells contain 47 chromosomes. Describe the difference in the chromosomes of each. 11. Do chromosomes come in homlogous pairs in all humans? Give examples to support your answer. 12. Which syndrome is represented by the karyotype in Figure 5? Figure 4 7 6. (a) How many chromosomes are in the body cells of a person with Down syndrome? (b) Describe the chromosome makeup of the gametes of a person with Down syndrome. 7. Name two disorders that result from nondisjunction of the sex chromosomes. Figure 5 2000X NEL 4.5 Atypical Meiosis 129
4.6 Prenatal Procedures (a) (b) Figure 1 An ultrasound involves using sound waves to produce an image of the fetus (a). The image is called a sonogram (b). LEARNING TIP The photographs and diagrams in this section will help you understand prenatal procedures. First, read the explanation of each procedure. Then look carefully at the related figure. 4A Investigation The Human Karyotype To perform this investigation, turn to page 139. In this investigation, you will create a karyotype of human chromosomes. Certain diseases are caused by mutated genes. For some diseases, scientists have identified which gene has the mutation. For example, scientists have identified the genes that, when mutated, cause cystic fibrosis and Huntington’s disease. The main symptom of cystic fibrosis, a buildup of mucus in the lungs, develops in childhood. Breathing is difficult, and most people do not live beyond their twenties. The symptoms of Huntington’s disease usually do not develop until people reach their mid-thirties or forties. Symptoms include personality changes and progressive loss of memory and muscle control. Scientists have been able to diagnose genetic disorders since the 1950s. Many disorders, such as Down syndrome and Turner syndrome, can be detected before a baby is born. Prenatal (before birth) tests most often confirm that fetuses are normal. Testing for genetic disorders prior to birth raises some ethical issues. Parents could decide to terminate the pregnancy. Knowing the gender of the fetus early on in the pregnancy may also be used as a reason to terminate the pregnancy. In most cases, however, the information helps parents make decisions that will better prepare them to raise their offspring. Ultrasound The technology that is most commonly used to detect abnormalities in the developing fetus is ultrasound. Ultrasound (Figure 1(a)) uses high-frequency sound waves to create a 3-D image, called a sonogram (Figure 1(b)), of the developing fetus. It is used to view the developmental progress of the fetus and to detect any physical abnormalities. It can also be used to determine the gender of the fetus. Amniocentesis In a procedure called amniocentesis (Figure 2), the doctor uses a syringe to remove amniotic fluid from the sac that surrounds the fetus. The amniotic fluid contains cells from the fetus, and these cells contain the chromosomes of the developing fetus. These cells are treated, allowed to reproduce, and then stained and placed on a microscope slide. A photo of the genetic material is used to produce a karyotype of the fetus. The test is done around the 20th week of pregnancy. 4A Investigation Since the 1970s, amniocentesis has been a common procedure used to view the chromosomes of fetuses in high-risk pregnancies. A pregnancy is considered to be high-risk when the mother is over the age of 35, the mother has already had a child with Down syndrome or a child with a defective spinal cord or brain, the mother or father has a genetic disease in the family, or the mother has had previous miscarriages. A miscarriage occurs when a fetus is involuntarily expelled from the womb before it has developed enough to survive on its own. Miscarriages can be caused by birth defects in the fetus, accidents, or illnesses. 130 <strong>Unit</strong> A <strong>Reproduction</strong> NEL
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CHAPTER 2 Cell Growth and Reproduct
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2.1 The Importance of Cell Division
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2.1 CHECK YOUR Understanding 1. Giv
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Figure 2 Plant cell structures cyto
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2.3 From DNA to Proteins You have l
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Did You KNOW? The Human Genome The
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LEARNING TIP Think about the sectio
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USING MITOCHONDRIAL DNA TO SOLVE MY
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centrioles nucleus chromosome spind
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2.4 CHECK YOUR Understanding 1. Wha
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LEARNING TIP Make connections to yo
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2.5 CHECK YOUR Understanding 1. Wha
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Binary fission allows for rapid pop
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2.6 CHECK YOUR Understanding 1. At
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could clone frogs, they were unable
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2A Investigation Observing Cell Div
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2B Investigation Determining the Ra
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CHAPTER 2 Review Cell Growth and Re
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Review Key Ideas and Vocabulary 1.
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CHAPTER 3 Sexual Reproduction KEY I
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3.1 Meiosis LEARNING TIP Scan the t
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Interphase Prophase Metaphase Anaph
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