Chapter 6, Problem 5CS

What is the genetic basis and phenotype for each of the following disorders (use proper genetic notation)? a. Edwards syndrome b. Patau syndrome c. Klinefelter syndrome d. Down syndrome

What is the importance of the comparison of traits between adopted and natural children in determining heritability?

Did the fact that Prince Albert and Queen Victoria were first cousins have anything to do with the fact that she carried the allele for hemophilia? Why or why not?

A pedigree analysis was performed on the family of a man with schizophrenia. Based on the known concordance statistics, would his MZ twin be at high risk for the disease? Would the twins risk decrease if he were raised in an environment different from that of his schizophrenic brother?

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?

Given the karyotype shown at right, is this a male or a female? Normal or abnormal? What would the phenotype of this individual be?

What are two examples of family support that would assist a child with a chronic condition?

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.