Imagine that you are in your late 30s or early 40s and decide that you want a child. You realize that you’re at greater risk of having a child with Down’s Syndrome. What sorts of genetic screening are available today? If you find out that this child has this condition, do you think it’s appropriate to have an abortion? Why or why not?

Would ISCI be an option? Why or why not? Jan, a 32-year-old woman, and her husband, Darryl, have been married for 7 years. They have attempted to have a baby on several occasions. Five years ago, they had a first-trimester miscarriage, followed by an ectopic pregnancy later the same year. Jan continued to see her OB/GYN physician for infertility problems but was very dissatisfied with the response. After four miscarriages, she went to see a fertility specialist, who diagnosed her with severe endometriosis and polycystic ovarian disease (detected by hormone studies). The infertility physician explained that these two conditions were hampering her ability to become pregnant and thus making her infertile. She referred Jan to a genetic counselor. At the appointment, the counselor explained to Jan that one form of endometriosis (MIM 131200) can be a genetic disorder, and that polycystic ovarian disease can also be a genetic disorder (MIM 184700) and is one of the most common reproductive disorders among women. The counselor recommended that a detailed family history of both Jan and Darryl would help establish whether Jans problems have a genetic component and whether any of her potential daughters would be at risk for one or both of these disorders. In the meantime, Jan is taking hormones, and she and Darryl are considering alternative modes of reproduction. Using the information in Figure 16.4, explain the reproductive options that are open to Jan and Darryl.

The following family has a history of inherited breast cancer. Betty (grandmother) does not carry the gene. Don, her husband, does. Dons mother and sister had breast cancer. One of Betty and Dons daughters (Sarah) has breast cancer; the other (Karen) does not. Sarahs daughters are in their 30s. Dawn, 33, has breast cancer; Debbie, 31, does not. Debbie is wondering if she will get the disease because she looks like her mother. Dawn is wondering if her 2-year-old daughter (Nicole) will get the disease. a. Draw a pedigree indicating affected individuals and identify all individuals. b. What is the most likely mode of inheritance of this trait? c. What are Dons genotype and phenotype? d. What is the genotype of the unaffected women (Betty and Karen)? e. A genetic marker has been found that maps very close to the gene. Given the following marker data for chromosomes 4 and 17, which chromosome does this gene map to? f. Using the same genetic marker, Debbie and Nicole were tested. The results are shown in the following figure. Based on their genotypes, is either of them at increased risk for breast cancer?

A couple has had a child born with neurofibromatosis. They come to your genetic counseling office for help. After taking an extensive family history, you determine that there is no history of this disease on either side of the family. The couple wants to have another child and wants to be advised about the risks of that child having neurofibromatosis. What advice do you give them?

________ Although the incidence of neural tube defects in the United States declined post-folic acid fortification, some women are still at risk. Which of the following options represents a risk group for inadequate folate status and a neural tube defect affected pregnancy? a. Non-Hispanic Black women b. Non-Hispanic White women c. Asian Americans d. Hispanic Americans

Birth Defects and Multiple Births A woman who carries multiple offspring at the same time increases the risk of some birth defects. FIGURE 42.18 shows the results of Yiwei Tang's study of birth defects reported in Florida from 1W6 to 2000. Tang compared the incidence of various defects among single and multiple births. She calculated the relative risk for each type of defect based on type of birth, and corrected for other differences that might increase risk such as maternal age, income, race, and medical care during pregnancy. A relative risk of less than 1 means that multiple births pose less risk of that defect occurring. A relative risk greater than 1 means multiples are more likely to have a defect. FIGURE 42.18 Prevalence, per 10,000 live births, of various types of birth defects among multiple aria single births. Relative risk for each defect is given after researches adjusted for the motor's age, race, previous adverse pregnancy experience, education, Medicaid participation during pregnancy, as well as the infant's sex and number of siblings. 4. Does a multiple pregnancy increase the relative risk of chromosomal defects in offspring?

Zoe has cystic fibrosis. Which of the following is the most likely explanation? Zoe probably inherited one faulty allele from her father, who is a earner, and one normal allele from her mother. Zoe probably inherited one faulty allele from her mother, who must also have cystic fibrosis, and one normal allele from her father. Zoe must have inherited faulty alleles from both parents, both of whom must also have cystic fibrosis, Zoe must have inherited faulty alleles from both parents, both of whom are earners.

If the child showed a cleft lip through ultrasound analysis and the parents then started blaming each other (because Sue is a smoker and Tim was born with the defect), how would you counsel them? Sue and Tim were referred for genetic counseling after they inquired about the risk of having a child with a cleft lip. Tim was born with a mild cleft lip that was surgically repaired. He expressed concern that his future children could be at risk for a more severe form of clefting. Sue was in her 12th week of pregnancy, and both were anxious about the pregnancy because Sue had had a difficult time conceiving. The couple stated that they would not consider terminating the pregnancy for any reason but wanted to be prepared for the possibility of having a child with a birth defect. The genetic counselor took a three-generation family history from both Sue and Tim and found that Tim was the only person to have had a cleft lip. Sues family history showed no cases of cleft lip. Tim and Sue had several misconceptions about clefting, and the genetic counselor spent time explaining how cleft lips occur and some of the known causes of this birth defect. The following list summarizes the counselors discussion with the couple. Fathers, as well as mothers, can pass on genes that cause clefting. Some clefts are caused by environmental factors, meaning that the condition didnt come from the father or the mother. One child in 33 is born with some sort of birth defect. One in 700 is born with a cleft-related birth defect. Most clefts occur in boys; however, a girl can be born with a cleft. If a person (male or female) is born with a cleft, the chances of that person having a child with a cleft, given no other obvious factor, is 7 in 100. Some clefts are related to identifiable syndromes. Of those, some are autosomal dominant. A person with an autosomal dominant gene has a 50% probability of passing the gene to an offspring. Many clefts run in families even when there does not seem to be any identifiable syndrome present. Clefting seems to be related to ethnicity, occurring most often among Asians, Latinos, and Native Americans (1 : 500); next most often among persons of European ethnicity (1 : 700); and least often among persons of African origin (1 : 1,000). A cleft condition develops during the fourth to the eighth week of pregnancy. After that critical period, nothing the mother does can cause a cleft. Sometimes a cleft develops even before the mother is aware that she is pregnant. Women who smoke are twice as likely to give birth to a child with a cleft. Women who ingest large quantities of vitamin A or low quantities of folic acid are more likely to have children with a cleft. In about 70% of cases, the fetal face is clearly visible using ultrasound. Facial disorders have been detected at the 15th gestational week of pregnancy. Ultrasound can be precise and reliable in diagnosing fetal craniofacial conditions.

Should he go ahead and enroll on the chance that he would receive the DNA vaccine and that it would be more effective than chemotherapy? Bruce and his parents moved to a semi-tropical region of the United States when he was about 3 years old. He loved to be outside year-round and swim, surf, snorkel, and play baseball. Bruce was fair-skinned, and in his childhood years, was sunburned quite often. In his teen years, he began using sunscreens, and although he never tanned very much, he did not have the painful sunburns of his younger years. After graduation from the local community college, Bruce wanted an outdoor job and was hired at a dive shop. He took people out to one of the local reefs to snorkel and scuba dive. He didnt give a second thought to sun exposure because he used sunscreen. His employer did not provide health insurance, so Bruce did not go for annual checkups, and tried to stay in good health. In his late 20s, Bruce was injured trying to keep a tourist from getting caught between the dive boat and the dock. He went to an internist, who treated his injury and told Bruce he was going to give him a complete physical exam. During the exam, the internist noticed a discolored patch of skin on Bruces back. She told him that she suspected Bruce had skin cancer and referred him to a dermatologist, who biopsied the patch. At a follow-up visit, Bruce was told that he had melanoma, a deadly form of skin cancer. Further testing revealed that the melanoma had spread to his liver and his lungs. The dermatologist explained that treatment options at this stage are limited. The drugs available for chemotherapy have only temporary effects, and surgery is not effective for melanoma at this stage. The dermatologist recommended that Bruce consider entering a clinical trial that was testing a DNA vaccine for melanoma treatment. These vaccines deliver DNA encoding a gene expressed by the cancer cells to the immune system. This primes the immune system to respond by producing large quantities of antibodies that destroy melanoma cells wherever they occur in the body. A clinical trial using one such DNA vaccine was being conducted at a nearby medical center, and Bruce decided to participate. At the study clinic, Bruce learned that he would be in a Phase Ill trial, comparing the DNA vaccine against the standard treatment, which is chemotherapy, and that he would be randomly assigned to receive either the DNA vaccine or the chemotherapy. He was disappointed to learn this. He thought he would be receiving the DNA vaccine.

A teratogen is an agent that produces nongenetic abnormalities during embryonic or fetal development. Suppose a teratogen is present at conception. As a result, during the first mitotic division the centromeres fail to divide. The teratogen then loses its potency and has no further effect on the embryo. What is the chromosomal complement of this embryo?