The correct answer appears first and is boldface.

1. b. Gary's father can contribute either an X or a Y chromosome; it is the Y chromosome that determines whether the individual will develop as male.

a. Gary's mother normally contributes only one of her two X chromosomes to the zygote; this chromosome does not distinguish males from females.

c. Although many traits may be passed along from Gary's grandfather, Gary's sex will be determined by his father's sex chromosomes.

d. Although many traits may be passed along from Joe's grandmother, Gary's sex will be determined by his father's sex chromosomes.

2. c. The gametes (either the egg or sperm cell) contain only half the number of chromosomes (or twenty-three) compared to other cells in the human body, which contain forty-six chromosomes.

a. The autosomes comprise the twenty-two pairs of homologous chromosomes in each cell and exclude only the sex chromosomes. Cells would not normally contain these forty-four chromosomes by themselves.

b. A zygote or fertilized egg contains the full complement of forty-six chromosomes as a result of the contribution of twenty-three chromosomes from each gamete (egg and sperm cell).

d. An allele is a variant of a particular gene and is not visible in a photomicrograph. Genes number in the tens of thousands.

3. c. The gene must be recessive and can be expressed in the phenotype only if both genes (one from the mother, one from the father) contain the instructions for blonde hair.

a. If the gene for red hair was dominant, at least one of Karen's parents would also have blonde hair.

b. The term heterozygous refers to a genotype in which two alleles of a gene are different. A single gene cannot itself be heterozygous, but it can be part of a heterozygous genotype.

d. With the information given, it is possible to determine that both of Karen's parents must carry the recessive gene for blonde hair. Karen received both recessive genes and thus has red hair in her phenotype.

4. d. Ultrasound is completely non-invasive. Ultrasound uses external waves to gauge age and size of the fetus.

a Choronic villus sampling requires an invasive procedure involving a biopsy of the villi surrounding the chorion, a membrane surrounding the fetus.

b Amniocentesis requires an invasive procedure involving insertion of a needle through the uterine wall to remove a sample of amniotic fluid.

c Maternal blood screen involves taking a sample of the mother's blood. Although it is not invasive in regards to the fetus, it still is invasive in regards to the mother.

5. b. Individuals with sickle cell anemia, an autosomal recessive disorder, display symptoms of the type described. Individuals with sickle cell trait--that is, who possess a heterozygous genotype where only one member of the pair of genes codes for sickle cell anemia--appear to be more resistant to malaria.

a. Huntington's disease is not found more frequently in regions of the world where malaria occurs than in other regions, and the symptoms--personality change, loss of motor control, and mental impairment--are quite different.

c. Phenylketonuria is not found more frequently in regions of the world where malaria occurs than in other regions, and the symptoms, which include mental retardation early in development, are far different.

d. Fragile X syndrome, a sex-linked disorder, is not found more frequently in regions of the world where malaria occurs than in other regions, and the symptoms--mental retardation and unique facial and body features--are different.

6. c. Males are more likely to have a recessive disorder than females; therefore, Stephen is more likely to have the disorder.

a. If Maxine and Stephen were identical twins, they would be equally likely to have the disorder; however, since they are of the opposite sex, they must be fraternal twins. Males are more likely to have a recessive disorder than females.

b. Males are more likely to have a recessive disorder than females; therefore, Maxine is less likely to have the disorder.

d. Because males have only one X chromosome, they are more likely to have a recessive disorder than females, who have a second allele to mask the recessive one. Therefore, Stephen, the male twin, is more likely to have the disorder.

7. d. Children with William's disease are characterized by the features described in the question.

a. Fragile syndrome is a common cause of mental retardation, however, these children do not have the language facility that children with William's syndrome posses.

b. Children' with Down syndrome are characterized by an epicanthal fold of the eye, flattened facial features and mental retardation.

c. PKU can lead to mental retardation if children are not placed on a low-protein diet. Infant testing has practically eliminated this as a cause of mental retardation in the US.

8. d. An extra sex chromosome does seem to increase an individual's susceptibility to abnormal development. However, many people with an XXY complement of chromosomes display normal development, especially when reared in a supportive environment.

a. No infants who inherited an extra chromosome 5 as part of their genotype have been reported to survive.

b. Infants who inherited an extra chromosome 13 have been reported to survive. However, their development does not proceed normally.

c. Occasionally infants are born with an extra chromosome 21 (Down syndrome) and can often live for many years. However, mental retardation consistently accompanies this chromosomal disorder, and development is dramatically slowed.

9. c. A genetic counselor can provide an analysis of the genotype of prospective parents and provide estimates of the likelihood of bearing a child with a genetic disorder.

a. Although a psychologist may be helpful to Ellen if she wants to discuss her distress over her family history, a psychologist could not identify Ellen's genotype.

b. A general medical doctor would not be likely to do genetic screening.

d. Family members can be understanding and supportive, but they cannot provide Ellen with an accurate analysis of her genotype.

10. d. Because Celeste is over thirty-five years of age, she is at risk for giving birth to a child with trisomy 21. To determine whether the fetus she is carrying has trisomy 21, Celeste can undergo amniocentesis.

a. Although Celeste is already a mother, she is above age thirty-five and therefore is at risk for giving birth to a child with trisomy 21. Artificial insemination by donor may be an option, but she may not be a good candidate for such a procedure.

b. Given that Celeste is above age thirty-five, she is at risk for giving birth to a child with trisomy 21. Surrogate motherhood may not be a good option for women at risk for bearing a child with trisomy 21.

c. In vitro fertilization may not be a good option for women of Celeste's age who are at risk for bearing a child with trisomy 21.

11. b. By a careful laboratory examination of the number of chromosomes in fetal cells found in the amniotic fluid and obtained through amniocentesis, the Capoletto's could be assured of whether a fetus did or did not have Down syndrome.

a. An alpha fetoprotein test based on analysis of the properties of the mother's blood can provide an indication that the fetus may have Down syndrome. However, such a test only gives a probability of increased risk for the disorder.

c. Although ultrasound may reveal a picture of a fetus that has features suggestive of Down syndrome, it typically does not possess sufficient detail to detect such a disorder in the fetus.

d. Neither an alpha fetoprotein test nor ultrasound can provide a clear answer. However, amniocentesis can.

12. d. Because the Y chromosome is relatively small compared to the X chromosome, a procedure that is based on the total amount of DNA in a sperm sample offers a reasonably good possibility for increasing the probability of conceiving a girl.

a. Although astrologers may claim to be able to influence such matters, no evidence exists to support such a claim.

b. Although claims exist that the correct arrangement of furniture in a living space has an impact upon events, no evidence exists to support a claim for increasing the likelihood of giving birth to a girl.

c. Methods of procreation are sometimes argued to have an influence on whether a boy or girl is conceived, but the research has not provided strong support for such an assertion.

13. a. The correlation coefficient is a statistical measure for examining the degree of similarity among individuals and is appropriate in cases where a variable such as creativity varies along a continuum.

b. The concordance rate is a statistical measure that determines the percentage of twins who possess a particular trait. Since creativity varies along a continuum, the correlation coefficient provides a better measure for determining whether creativity is more similar among fraternal or identical twins.

c. Dominant-recessive relationships describe the complex ways in which alleles interact to determine the phenotype; analysis of these relationships is not a statistical procedure.

d. There is no statistical procedure called interactional analysis.

14. b. Since monozygotic twins have the same genotype, any observed differences would be attributed primarily to environmental factors.

a. Genotype refers to the inherent genetic makeup of an individual. No evidence exists to indicate that behavior influences the genotype.

c. The phenotype, which includes behavior, is a product of the genotype and the environment; the phenotype cannot be a cause of behavior.

d. Examining the effects of different environments on individuals who share the same genotype (monozygotic twins) reveals the influence of the environment on human traits and characteristics, not the influence of the genotype or the phenotype.

15. a. Whenever the effect of one variable on behavior depends on a second variable, an interaction between the two variables is said to have occurred. For example, because the effect of environment on intelligence depends on the child's genotype, the environment is said to interact with the genotype.

b. A correlation describes the relationship between two variables, but, as always, correlation does not imply causation. The statement that the environment's influence depends on the genotype implies a causal relationship.

c. Although canalization can be described as an interaction between genotype and environment, the term identifies a specific principle whereby the genotype resists all but extreme environmental influences on the phenotype.

d. Heritability is the estimated contribution that heredity or the genotype makes to the phenotype; environmental influences are excluded from this estimate.

16. a. Clorinda is larger and stronger than most girls her age and may be athletically inclined. Her choice of soccer as an after-school activity is consistent with her genotype and therefore is a good example of niche picking.

b. Passive factors are usually provided by caregivers and are not a result of the child's actions. Clorinda's role in choosing soccer is active, not passive.

c. Clorinda's large stature is most likely a result of polygenic influences; however, the term polygenic ("many genes") does not define the tendency to actively select an environment that is consistent with a genotype.

d. A person's genotype is said to be homozygous when both genes have the same allelic form. This would have no direct effect on Clorinda's choice of soccer as an after-school activity.

17. b. Children often try to set themselves apart from other members of the family. Even identical twins who have the same genetic makeup may actively seek out a unique niche within the family.

a. The genotype refers to the genetic potential underlying traits and behaviors and is not an experiential factor.

c. The phenotype refers to the observable traits and behaviors displayed by an individual. Both the genotype and experience contribute to the phenotype.

d. The shared environment refers to the kinds of experiences children within the family have in common. These experiences are expected to promote similarities rather than differences in the behavior of siblings.

18. b. Studies of infants of different ethnic groups have implicated genetic differences in temperament.

a. Studies that have investigated differences in behavioral characteristics among infants of different cultures have attributed such differences to the genotype, not to the environment.

c. Although sociocultural factors certainly influence behavioral development, studies examining behavioral differences among infants of various cultural groups have implicated genetic factors.

d. Studies of infants of different ethnic groups have implicated genetic differences in temperament.

19. d. An evocative link refers to the idea that the child actively influences their own environment. By performing well in school, this child evokes a certain behavior from the teacher, which in turn can influence that child's future development.

a This is an example of a passive link. The parents are providing a certain environment to the child, regardless of the child's behavior.

b. This example actually works against the idea of niche- picking, as the child is being forced to interact in an environment that is not what he or she would have selected.

c Although a good student might decide to take on extra work, as stated we do not know if this extra work influences that child's environment.