Chapter 1

1. In the Hopi culture, people with albinism were considered special and given special status. Because extensive exposure to sunlight could be damaging or deadly, Hopi men with albinism did no agricultural work. Albinism was a considered a positive trait rather than a negative physical condition, which gave people with albinism a mating advantage and thus increased the frequency of the albino mutation. Finally, the small population size of the Hopi tribe may have helped increase the frequency of the albino mutation owing to chance.

16. Evolution is genetic change over time. For evolution to take place, genetic variation must first arise, and then evolutionary forces must change the proportion of genetic variants over time. Genetic variation is therefore the basis of all evolutionary change.

17. (a) Transmission genetics; (b) population genetics; (c) population genetics; (d) molecular genetics; (e) molecular genetics; (f) transmission genetics.

18. Genetics is old in the sense that humans have been aware of hereditary principles for thousands of years and have applied them since the beginning of agriculture. It is very young in the sense that the fundamental principles were not uncovered until Mendel’s time, and the structure of DNA and the principles of recombinant DNA were discovered only within the past 60 years.

19. (a) Germ-plasm theory; (b) preformationism; (c) inheritance of acquired characteristics; (d) pangenesis.

20. 1. Pangenesis postulates that pieces of genetic information travel from all parts of the body to the reproductive organs, and that genetic information is then conveyed to the embryo. According to the germ-plasm theory, gamete-producing cells found within the reproductive organs contain a complete set of genetic information that is passed to the gametes. Pangenesis and the germ-plasm theory are similar in that both propose that genetic information is contained in discrete units that are passed on to offspring. They differ in where that genetic information resides. In pangenesis, it resides in different parts of the body and must travel to the reproductive organs. In the germ-plasm theory, all the genetic information is already in the reproductive cells.

    2. Preformationism holds that the sperm or egg contains a miniature preformed adult called a homunculus. In development, the homunculus grows to produce an offspring. Only one parent contributes genetic traits to the offspring. Blending inheritance requires contributions of genetic material from both parents. The genetic contributions from the parents blend to produce the genetic material of the offspring. Having been blended, the genetic material cannot be separated in future generations.

    3. The inheritance of acquired characteristics postulates that traits acquired in a person’s lifetime alter the genetic material and can be transmitted to offspring. Our modern theory of heredity states that offspring inherit genes located on chromosomes passed to them by their parents. These chromosomes segregate in meiosis in the parent’s germ cells and are passed into the gametes.

21. 1. Eukaryotic cells have a nucleus containing chromosomal DNA and possess internal membrane-bounded organelles. Prokaryotic cells have neither of these features.

    2. A gene is a basic unit of hereditary information, usually encoding an RNA molecule or a protein. Alleles are variant forms of a gene, arising through mutation.

    3. The genotype is the set of genes or alleles inherited by an organism from its parent(s). The expression of the genes of a particular genotype, through interaction with environmental factors, produces the phenotype, the observable trait.

    4. Both are nucleic acid polymers. RNA contains a ribose sugar, whereas DNA contains a deoxyribose sugar. RNA also contains uracil as one of the four bases, whereas DNA contains thymine. The other three bases are common to both DNA and RNA. Finally, DNA is usually double stranded, consisting of two complementary strands, whereas RNA is single stranded.

    5. Chromosomes are structures consisting of DNA and associated proteins. The DNA contains the genetic information.

22. Type of albinism	Phenotype	Gene mutated
    OCA2	Pigment reduced in skin, hair, and eyes, but small amount of pigment acquired with age; visual problems	OCA2
    OCA1B	General absence of pigment in hair, skin, and eyes, but there may be small amount of pigment; does not vary with age; visual problems	Gene that encodes tyrosinase
    OCA1A	Complete absence of pigment; visual problems	Gene that encodes tyrosinase
    OCA3	Some pigment present; sun sensitivity and visual problems	Gene that encodes tyrosinase-related protein 1
    OASD	Lack of pigment in the eyes and deafness later in life	Unknown
    OA1	Lack of pigment in the eyes but normal elsewhere	GPR143
    ROCA	Bright copper-red coloration in skin and hair of Africans; dilution of color in iris	Gene that encodes tyrosinase-related protein 1
    OCA4	Reduced pigmentation	MATP

26. All genomes must have the ability to store complex information and to vary. The blueprint for the entire organism must be contained within the genome of each reproductive cell. The information has to be in the form of a code that can be used as a set of instructions for assembling the components of the cells. The genetic material of any organism must be stable, be replicated precisely, and be transmitted faithfully to the progeny, but must be capable of mutating.

28. Legally, she is not required to inform her children or other relatives about her test results, but people may have different opinions about her moral and parental responsibilities. On the one hand, she has the legal right to keep any medical information, including the results of genetic testing, private. On the other hand, her children may be at an increased risk of developing these disorders and might benefit from that knowledge. For example, the risk of colon cancer can be reduced by regular examinations so that tumors can be detected and removed before they become cancerous. Some people might argue that her parental responsibilities include providing her children with information about possible medical problems. Another issue to consider is the possibility that her children or other relatives might not want to know their genetic risk, particularly for a disorder such as Alzheimer disease for which there is no cure.

29. 1. Having the genetic test removes doubt about the potential for the disorder: you are either susceptible or not. Knowing about the potential of a genetic disorder enables you to make lifestyle changes that might lessen the effect of the disease or lessen the risk. The types and nature of future medical tests could be guided by the result of genetic testing, thus allowing for early warning and screening for the disease. The knowledge could also enable you to make informed decisions about having children, given the potential of passing the trait to your offspring. Additionally, by knowing what to expect, you could plan your life accordingly. Reasons for not having the test typically concern the potential for testing positive for susceptibility to the genetic disease. If the susceptibility is detected, there is potential for discrimination. Knowledge of the potential future condition could lead to psychological difficulties in coping with the anxiety of waiting for the disease to manifest.

    2. There is no “correct” answer, but some of the reasons for wanting to be tested are that the test would remove doubt about the susceptibility, particularly if family members have had the genetic disease; and that either a positive or a negative result would allow for informed planning of lifestyle, medical testing, and family choices in the future.