Unit A Reproduction

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FIGHTING HUNTINGTON’S DISEASE Genetically modified mice are helping Vancouver scientists learn more about this deadly genetic disease. Tech CONNECT Would you want to know right away if you carried the gene? Would you rather wait and see if you developed the symptoms? Children of people with Huntington’s disease must ask themselves these questions. Huntington’s disease is a disease of the nervous system that is characterized by loss of memory, reasoning, and judgment, as well as involuntary jerky movements of the limbs, head, and neck. The onset of Huntington’s disease is usually between 30 and 50 years of age, and because there is currently no cure, death occurs from complications 10 to 15 years after the onset of the disease. People with Huntington’s disease usually die from falls or choking. Huntington’s disease is the result of a mutation in the gene that codes for huntingtin protein, a protein that is essential for proper nerve cell functioning. Amino acids are the building blocks of proteins. Normally, the huntingtin protein has many molecules of the amino acid glutamine, usually between 10 and 35 in a row. In people with Huntington's disease, the mutated gene creates a protein that has over 40 glutamine molecules in a row. The extra glutamines change the shape of the protein, which in turn causes nerve cell death. The death of nerve cells is the cause of the symptoms and progression of Huntington’s disease (Figure 1). Scientists, such as Dr. Michael Hayden at the Centre for Molecular Medicine and Therapeutics in Vancouver, have developed special mice that serve as models to study this disease. These mice were developed by transferring new genes into the nuclei of fertilized mouse embryos. The genetically modified mice have symptoms that resemble Huntington’s disease. As the mice mature and develop symptoms, scientists learn about the disease mechanisms and potential treatments for Huntington’s disease. There is a test to determine the base sequence of the gene on chromosome 4, which codes for huntingtin protein. It is the only reliable way to determine if an individual will develop Huntington’s disease. Interestingly, many people who have a parent with Huntington’s disease do not want to get tested. It is an individual choice. Think of what it would be like to wonder, every time you tripped or dropped a glass, if you were getting the disease. Without a cure, however, would wondering be better than facing the certainty of the disease? Figure 1 Cross sections of a brain from a person who died from Huntington’s disease (top) and a normal brain (bottom). In the Huntington’s brain, notice the large spaces created by the death of cells in these areas of the brain. NEL 133
4.7 Reproductive Technologies LEARNING TIP Preview Section 4.7, and read the headings. What types of reproductive technologies will you be reading about in this section? Although reproduction is a normal part of human life, complications can arise at all stages of the human reproductive cycle. Reproductive technologies are changing the ways that babies are conceived and born, and are shaping the laws that determine parenthood and responsibility. What are some of the ways that humans have overcome barriers to reproduction? Are there new technologies on the horizon? There are many reasons why couples are infertile and are unable to have babies. The man may not be able to produce enough healthy sperm. The oviducts of the woman may be blocked, or the ovaries may not be functioning properly. There may not be enough of the proper hormone at the correct time in the woman’s cycle. Whatever the reason, couples can get advice and treatment from doctors who specialize in fertility problems. There are a number of reproductive technologies that doctors can use to treat infertility. Fertility Drugs Fertility drugs stimulate the production of hormones that affect the action of the female’s follicles. When a woman takes these drugs, more eggs mature and are released from the ovary. This increases the chances of conception. In fact, taking fertility drugs often results in multiple births (twins, triplets). People who undergo any of the following procedures are often prescribed fertility drugs as well. egg cell catheter ovary Figure 1 In intrauterine insemination, the sperm are collected and placed in a syringe. They are then injected into the uterus using a catheter. The sperm move into the oviduct to fertilize the egg. Artificial Insemination Artificial insemination involves introducing sperm into the reproductive tract of the female by a method other than sexual intercourse. In humans, several million sperm are needed to ensure successful fertilization. One cause of infertility can be a low sperm count. If the male has a low sperm count, his sperm can be collected over time and then artificially inserted into the female by a doctor. If the male produces no living sperm at all, couples can use sperm from an anonymous donor, obtained from a sperm bank. Intrauterine Insemination In intrauterine insemination, sperm is collected from the male and placed directly into the female’s uterus (Figure 1), rather than into the vagina, as in artificial insemination. The sperm is placed high up in the uterus at the time of ovulation. Normally, many sperm cells die as they travel from the vagina to the oviducts. This technology ensures that as many sperm as possible reach the egg. 134 <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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LEARNING TIP Make connections to yo
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Binary fission allows for rapid pop
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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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allele for straight hairline homolo
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Unit A Reproduction

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