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BIO305: Genetics

Unit 5: Chromosomal Genetics and Structure   Karyotyping is the study of the physical structure of chromosomes that can be observed through staining. Although karyotyping has been around since the 1800s, it took until the 1950s to understand that humans had 46 chromosomes. Our entire genome resides in chromosomes. The human genome consists of 22 pairs of chromosomes and a pair of sex chromosomes; two X chromosomes mean a female, while an XY combination means a male. When a baby does not have exactly 46 chromosomes, any number of diseases can result, but most commonly aneuploidy is lethal. For example, when a baby has less than 46 chromosomes, genetic defects arise. Extra or missing copies of sex chromosomes also result in disease. Down syndrome occurs in the event of trisomy 21, where there are three copies of chromosome 21. In addition, pieces of chromosomes can sometimes be missing, duplicated, or even transferred to another chromosome, which also results in disease.

Unit 5 Time Advisory
This unit should take you approximately 9.25 hours to complete.
 
☐    Subunit 5.1: 3 hours
 
☐    Subunit 5.2: 1 hour
 
☐    Subunit 5.3: 1.25 hours
 
☐    Subunit 5.4: 2 hours
 
☐    Subunit 5.5: 2 hours

Unit5 Learning Outcomes
Upon successful completion of this unit, you will be able to: - define eukaryotic chromosomal structure and karyotyping, and explain the process of non-disjunction and how it can lead to chromosomal abnormalities; - explain ploidy; - compare and contrast as well as discuss chromosomal rearrangement and aneuploidy; - identify chromosomal abnormalities with the help of karyotyping; - describe how non-disjunction leads to chromosomal abnormalities; - compare and contrast as well as discuss structural abnormalities of chromosomes; and - identify syndromes caused by aneuploidy.

5.1 The Structure of Eukaryotic Chromosomes   5.1.1 Homologous Chromosomes   - Reading: Dr. John W. Kimball’s Biology Pages: “Chromosomes” Link: Dr. John W. Kimball’s Biology Pages: “Chromosomes” (HTML)
 
Instructions: Read this article, which will provide you with an overview of chromosomes, karyotypes, homologous chromosomes, and sex chromosomes. This reading also covers the topic outlined in subunit 5.1.3.
 
Reading this article should take approximately 1 hour.
 
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5.1.2 Sex Chromosomes   - Reading: Dr. John W. Kimball’s Biology Pages: “Sex Chromosomes” Link: Dr. John W. Kimball’s Biology Pages: “Sex Chromosomes” (HTML)
 
Instructions: Read this article, which describes the sex chromosomes in the X-Y sex determination system.
 
Reading this article should take approximately 1 hour.
 
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5.1.3 Ploidy   - Reading: Dr. John W. Kimball’s Biology Pages: “Polyploidy” Link: Dr. John W. Kimball’s Biology Pages: “Polyploidy” (HTML)
 
Instructions: Read this article about polyploidy – having multiple copies of chromosomes – which has been an important part of plant evolution. In fact, many researchers suspect that it is thanks to this process, the doubling of chromosome number, that we have many different plant species today.
 
Reading this article should take approximately 1 hour.
 
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5.2 Chromosome Rearrangements   - Reading: Dr. John W. Kimball’s Biology Pages: “Mutations” Link: Dr. John W. Kimball’s Biology Pages: “Mutations” (HTML)
 
Instructions: Read the following sections: “Insertions and Deletions (Indel),” “Duplication,” and “Translocations,” focusing on the diseases discussed in each section. Note that chromosomal rearrangements may cause disorders such as fragile X syndrome, polyglutamine disease, and muscular dystrophy.
 
Reading these sections should take approximately 1 hour.
 
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5.3 Non-Disjunction and Aneuploidy   - Reading: Clinton Community College: Dr. Michael Gregory’s “Non-disjunction” Link: Clinton Community College: Dr. Michael Gregory’s “Non-disjunction” (HTML)
 
Instructions: Read this article, which gives an informative diagrammatic representation of the process of non-disjunction.
 
Reading this article should take approximately 30 minutes.
 
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  • Reading: Massachusetts Institute of Technology: Professor Gerry Fink’s “Lecture 32: Chromosome Anomalies I” Link: Massachusetts Institute of Technology: Professor Gerry Fink’s “Lecture 32: Chromosome Anomalies I” (PDF)
     
    Instructions: Select the PDF link for “Lecture 32: Chromosome Anomalies I,” and read these lecture notes. These lecture notes explain how missteps during meiosis lead to abnormal chromosome numbers in the gametes. This text is technical, so please plan to read it several times for a full understanding.
     
    Reading these lecture notes should take approximately 45 minutes.
     
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5.4 Autosomal Chromosome Disorders   - Reading: National Institute of Health’s Genetics Home Reference: “Can Changes in the Number of Chromosomes Affect Health and Development?” Link: National Institute of Health’s Genetics Home Reference: “Can Changes in the Number of Chromosomes Affect Health and Development?” (HTML)
 
Instructions: Read this article on chromosomal disorders in humans.
 
Reading this article should take approximately 30 minutes.
 
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5.4.1 Down Syndrome   - Reading: National Institute of Health’s Genetics Home Reference: “Down Syndrome” Link: National Institute of Health’s Genetics Home Reference: “Down Syndrome” (HTML)
 
Instruction: Read this article on Down syndrome. Down syndrome is a trisomy, which becomes more frequent with the increasing age of the mother.
 
Reading this article should take approximately 30 minutes.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

5.4.2 Patau Syndrome   - Reading: National Institute of Health’s Genetics Home Reference: “Trisomy 13” Link: National Institute of Health’s Genetics Home Reference: “Trisomy 13” (HTML)
 
Instruction: Read this article. Patau syndrome is a trisomy, which, like Down Syndrome, becomes more frequent with the increasing age of the mother, but Patau syndrome results in more severe developmental abnormalities than Down syndrome.
 
Reading this article should take approximately 30 minutes.
 
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5.4.3 Edwards Syndrome   - Reading: National Institute of Health’s Genetics Home Reference: “Trisomy 18” Link: National Institute of Health’s Genetics Home Reference: “Trisomy 18” (HTML)
 
Instruction: Read this article. Edwards syndrome is a trisomy, which, like Down syndrome and Patau syndrome, becomes more frequent with the increasing age of the mother. Edwards syndrome results in the most severe developmental abnormalities, and fetuses may die during pregnancy.
 
Reading this article should take approximately 30 minutes.
 
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5.5 Sex Chromosome Disorders   5.5.1 Turner Syndrome   - Reading: National Institutes of Health’s Genetics Home Reference: “Turner Syndrome” Link: National Institutes of Health’s Genetics Home Reference: “Turner Syndrome” (HTML)
 
Instructions: Read this article. Note that Turner syndrome is an aneuploidy; it is the only viable human monosomy. Optionally, you may also want to explore the embedded links to learn more on Turner syndrome.
 
Reading this article should take approximately 30 minutes.
 
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5.5.2 Klinefelter Syndrome   - Reading: National Institutes of Health’s Genetics Home Reference: “Klinefelter Syndrome” Link: National Institutes of Health’s Genetics Home Reference: “Klinefelter Syndrome” (HTML)
 
Instructions: Read this article. Note that Klinefelter syndrome is an aneuploidy. Optionally, you may also want to explore the embedded links to learn more about Klinefelter syndrome.
 
Reading this article should take approximately 30 minutes.
 
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5.5.3 Triple X Syndrome   - Reading: National Institutes of Health’s Genetics Home Reference: “Triple X Syndrome” Link: National Institutes of Health’s Genetics Home Reference: “Triple X Syndrome” (HTML)
 
Instructions: Read this article. Note that triple X syndrome is an aneuploidy. Optionally, you may also want to explore the embedded links to learn more on triple X syndrome.
 
Reading this article should take approximately 30 minutes.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

5.5.4 Fragile X Syndrome   - Reading: National Institutes of Health’s Genetics Home Reference: “What Is Fragile X Syndrome?” Link: National Institutes of Health’s Genetics Home Reference: “What Is Fragile X Syndrome?” (HTML)
 
Instructions: Read this article. Note that fragile X syndrome is the most common genetically inherited mental retardation, and it is more common in men than in women. The X chromosome becomes fragile during a diagnostic staining procedure. The X chromosome is not fragile in vivo. Optionally, you may want to explore the embedded links to learn more on fragile X syndrome.
 
Reading this article should take approximately 30 minutes.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.