Lesson 2 Assignment #1: Genetic Information Resources The volume and complexity of information on genetics is overwhelming to many students (and teachers) of introductory child development courses. However, the National Institutes of Health cooperate with other organizations and agencies to provide via the Internet detailed searchable databases for persons seeking information on genetics, genetic counseling, and genetic testing. In this assignment, I would like you to “walk through” some websites. Two reliable sites are: National Center for Biotechnology Information (www.ncbi.nlm.nih.gov), and OMIM (Online Mendelian Inheritance in Man) ( www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=OMIM). While browsing these two sites create a summary of the information that would be available from the site. In other words, what kinds of information can one find at each of the sites? Who supports the site? Describe who might find the site useful. Lastly, select two abnormalities of the sex-linked chromosomes (not sex-linked genes) and two gene-linked abnormalities listed in chapter 2 and research the abnormalities on these sites or you may use other sites. Prepare a brief report (at least a substantive paragraph) on each abnormality from the information you observed from the sites. Be sure to cite your references and include complete citations. Please note Down syndrome is not a sex-linked chromosome disorder. CHAPTER TWO TEXT BELOW:Chromosomal Abnormalities Sometimes a gamete is formed in which the male’s sperm and/or the female’s ovum do not have their normal set of 23 chromosomes. The most notable examples involve Down syndrome and abnormalities of the sex chromosomes (see Figure 2.5).Down Syndrome An individual with Down syndrome has a round face, a flattened skull, an extra fold of skin over the eyelids, a protruding tongue, short limbs, and disabilities involving motor and intellectual development. The syndrome is caused by the presence of an extra copy of chromosome 21. It is not known why the extra chromosome is present, but the health of the male sperm or female ovum may be involved.Down syndrome A chromosomally transmitted form of intellectual disability, caused by the presence of an extra copy of chromosome 21.Down syndrome appears approximately once in every 700 live births. Women between the ages of 16 and 34 are less likely to give birth to a child with Down syndrome than are younger or older women. African American children are rarely born with Down syndrome.Sex-Linked Chromosomal Abnormalities Recall that a newborn normally has either an X and a Y chromosome, or two X chromosomes. Human embryos must possess at least one X chromosome to be viable. The most common sex-linked chromosomal abnormalities involve the presence of an extra chromosome (either an X or Y) or the absence of one X chromosome in females.Page 58Klinefelter syndrome is a chromosomal disorder in which males have an extra X chromosome, making them XXY instead of XY (Aksglaede & others, 2013). Males with this disorder have undeveloped testes, and they usually have enlarged breasts and become tall. A recent study revealed significant impairment in language, academic, attentional, and motor abilities in boys with the syndrome (Ross & others, 2012). Klinefelter syndrome occurs approximately once in every 800 live male births.Klinefelter syndrome A chromosomal disorder in which males have an extra X chromosome, making them XXY instead of XY.Fragile X syndrome is a genetic disorder that results from an abnormality in the X chromosome, which becomes constricted and often breaks. The physical appearance of children with fragile X syndrome often appears normal, although these children typically have prominent ears, a long face, a high-arched palate, and soft skin. Mental deficiency often is an outcome, but it may take the form of intellectual disability, a learning disability, or a short attention span. One study revealed that boys with fragile X syndrome were characterized by cognitive deficits in inhibition, memory, and planning (Hooper & others, 2008). This disorder occurs more frequently in males than in females, possibly because the second X chromosome in females negates the effects of the abnormal X chromosome (Fung & others, 2012).fragile X syndrome A genetic disorder involving an abnormality in the X chromosome, which becomes constricted and often breaks.Turner syndrome is a chromosomal disorder in females in which either an X chromosome is missing, making the person XO instead of XX, or part of one X chromosome is deleted. Females with Turner syndrome are short in stature and have a webbed neck (Kaur & Phadke, 2012). They might be infertile and have difficulty in mathematics, but their verbal ability often is quite good. Turner syndrome occurs in approximately 1 of every 2,500 live female births (Kim & others, 2011).Turner syndrome A chromosome disorder in females in which either an X chromosome is missing, making the person XO instead of XX, or the second X chromosome is partially deleted.XYY syndrome is a chromosomal disorder in which the male has an extra Y chromosome (Stochholm & others, 2012). Early interest in this syndrome focused on the belief that the extra Y chromosome found in some males contributed to aggression and violence. However, researchers subsequently found that XYY males are no more likely to commit crimes than are XY males (Witkin & others, 1976).XYY syndrome A chromosomal disorder in which males have an extra Y chromosome.Gene-Linked Abnormalities Abnormalities can be produced not only by an abnormal number of chromosomes but also by harmful genes (Johnson, 2012). More than 7,000 such genetic disorders have been identified, although most of them are rare.Phenylketonuria (PKU) is a genetic disorder in which the individual cannot properly metabolize phenylalanine, an amino acid. It results from a recessive gene and occurs about once in every 10,000 to 20,000 live births. Today, phenylketonuria is easily detected, and it is treated by a diet that prevents an excess accumulation of phenylalanine (Giovannini & others, 2012). If phenylketonuria is left untreated, however, excess phenylalanine builds up in the child, producing intellectual disability and hyperactivity. Phenylketonuria accounts for approximately 1 percent of institutionalized individuals who are intellectually disabled, and it occurs primarily in non-Latino Whites.phenylketonuria (PKU) A genetic disorder in which an individual cannot properly metabolize an amino acid. PKU is now easily detected but, if left untreated, results in intellectual disability and hyperactivity.The story of phenylketonuria has important implications for the nature-nurture issue. Although phenylketonuria is a genetic disorder (nature), how or whether a gene’s influence in phenylketonuria is played out depends on environmental influences because the disorder can be treated (nurture) using an environmental manipulation (Mehari & others, 2012). That is, the presence of a genetic defect does not inevitably lead to the development of the disorder if the individual develops in the right environment (one free of phenylalanine). This is one example of the important principle of heredity-environment interaction. Under one environmental condition (phenylalanine in the diet), intellectual disability results, but when other nutrients replace phenylalanine, intelligence develops in the normal range. The same genotype has different outcomes depending on the environment (in this case, the nutritional environment).Sickle-cell anemia, which occurs most often in African Americans, is a genetic disorder that impairs the functioning of the body’s red blood cells. Red blood cells carry oxygen to the body’s other cells and are usually shaped like a disk. In sickle-cell anemia, a recessive gene causes the red blood cell to become a hook-shaped “sickle” that cannot carry oxygen properly and dies quickly. As a result, the body’s cells do not receive adequate oxygen, causing anemia and early death (Dworkis & others, 2011; Eckman & Embury, 2011). About 1 in 400 African American babies is affected by sickle-cell anemia. One in 10 African Americans is a carrier, as is 1 in 20 Latin Americans. A National Institutes of Health (2008) panel concluded that the only FDA-approved drug (hydroxyurea) to treat sickle-cell anemia in adolescents and adults is not widely used. Research is currently being conducted in a study named Baby HUG to determine whether the drug works with babies (Alvarez & others, 2012).sickle-cell anemia A genetic disorder that affects the red blood cells and occurs most often in people of African descent.Other diseases that result from genetic abnormalities include cystic fibrosis, some forms of diabetes, hemophilia, spina bifida, and Tay-Sachs
