Chapter 1 Flashcards

Question

A change in allele frequency within a population over time leads to a. a genome. b. a phenotype. c. a genotype. d. mutations. e. evolution.

Answer 1

e. evolution.

Answer 2

d. Either DNA or RNA

Answer 3

c. DNA → RNA → protein

Answer 4

e. develop a method for sequencing DNA.

Answer 5

c. Hydrogen bond

Answer 6

b. allele.

Answer 7

d. Evolution

Answer 8

e. mutations.

Answer 9

b. chromosomes.

Answer 10

In most populations, there is fairly strong selection against albinism because albinos don’t produce melanin, causing their skin cells not to be protected from the damaging effects of sunlight. Also, the lack of melanin in their eyes causes them to have poor eyesight. Finally, in most cultures albinos are seen as abnormal, and they are not normally sought out for marriage and mating. Therefore, in most populations the alleles that cause albinism are selected against, and they decrease in frequency or are kept at a low level, causing the recessive trait to be rare.

Answer 11

Albinos occupy a privileged position among the Hopis of Black Mesa. In this culture, albinos are viewed as especially pretty, clean, and intelligent, and they often occupy positions of leadership. Albinos are celebrated in the villages as a sign of purity of Hopi blood in the community. Furthermore, albinos are often excused from normal male field labor because of their sensitivity to sunlight, causing them to be left behind in the village with the women during the daytime. This allows them extra mating opportunities compared to the other men of the village. Therefore, the alleles that cause albinism are either selected for in this culture or at least not selected against as strongly as in other cultures, allowing the trait to occur at a much higher frequency.

Answer 12

This example and others show that the effect of a particular allele cannot be evaluated outside of the context of the environment of the population in which the allele exists. A particular allele might be harmful in one environment but beneficial in another environment. Although we know of some alleles that seem to be harmful in all current environments, they might have been beneficial in the past or might be in the future.

Answer 13

(1) Short generation time (2) Sufficient numbers of progeny for study (3) Adaptability to a laboratory environment (4) Ability to be inexpensively housed and propagated (5) Small size

Answer 14

Researchers might want to study the process in fruit flies first because it would likely be easier to study it in fruit flies, and what is discovered in fruit flies might apply to humans. Fruit flies have been used for over 100 years as a model system to study animal genetics and development.

Answer 15

Strengths – Fruit flies have proven to be an excellent model system for studying aspects of biology that they share with humans. Fruit flies are simpler in structure and physiology than humans and have a much simpler genome. They are small and easy to raise, they have a short generation time, and they produce a large number of offspring. Their chromosomes have been mapped and their genomes analyzed extensively. It is relatively easy to isolate and study mutants that are defective in specific processes of interest. These characteristics make them ideal for genetic studies of biological processes. Weaknesses – Some aspects of fruit fly genetics and development are not shared with humans. Therefore, some features discovered in fruit flies will not apply directly to humans. Also, humans have many features that fruit flies lack. Fruit flies will not serve well as a model system for studying these features of human biology.

Answer 16

Despite the remarkable diversity of life on Earth, all genomes are encoded in nucleic acids. With few exceptions, the genetic code is common to all forms of life. Finally, the process by which genetic information is copied and decoded is remarkably similar for all forms of life.

Answer 17

Bacteria and viruses have their genetic material (DNA) organized into genes, just like other organisms, so the basics of inheritance are the same in bacteria and viruses, as in other organisms. The genetic systems of bacteria and viruses are simpler when compared to higher eukaryotic organisms such as mice, dogs, or humans: they have fewer genes, fewer chromosomes, and less DNA. Bacteria and viruses reproduce more quickly than higher eukaryotic organisms: the generation time is shorter than for mice, dogs, or humans. Bacteria and viruses are easy and less expensive to grow (take up less space, have less complicated nutritional needs) than vertebrates.

Answer 18

Answers will vary but might include pangenesis, inheritance of acquired characteristics, preformationism, or blending inheritance, which are all described in Section 1.1. Pangenesis – The idea that information needed to encode each body structure is stored in that structure and transported to the reproductive organs and passed to the embryo at conception. Inheritance of acquired characteristics – The idea that traits acquired through use during one’s lifetime can be passed to one’s offspring. Preformationism – The idea that the sperm or egg carries a tiny preformed person whose development simply involves enlargement. Blending inheritance – The idea that the genetic material is a fluid that gets blended during sexual reproduction between a male and female, resulting in the production of traits in the offspring that are blended intermediates of those of the parents.

Answer 19

Answers will vary but should include specific evidence or observations that support the idea. Examples: Pangenesis – It is reasonable to assume that the information needed to build a structure must reside in that structure. It is less obvious that the information might also reside in other structures. Therefore, it is reasonable to envision the information being stored in each structure and transported to the reproductive structures before being passed to the next generation. Inheritance of acquired characteristics – Observations to support this view would have been commonplace. For example, a man with a muscular physique would often have sons with muscular physiques. A talented musician often produced children with musical talent. Preformationism – It would have been hard for people before the late 1800s to imagine how a complex organism could build itself from a single undifferentiated cell. Indeed, the problem has occupied developmental biologists for over 100 years.

Answer 20

Answers will vary but should include specific evidence or observations that do not support the idea. Pangenesis – Observations of animals with body parts lost to injury producing normal offspring would not support pangenesis. Inheritance of acquired characteristics – Experiments were conducted in which body parts were removed and normal offspring were produced, showing that the acquired characteristic was not inherited. Also, experiments in which offspring are raised in an environment different from that of their parents and do not develop their parents’ traits would suggest that the environment influences development of these traits. Preformationism – Eventually better microscopes were produced that proved that gametes do not contain preformed people. Also, we eventually came to understand that both sperm and eggs contribute genetic information during sexual reproduction. Blending inheritance – Mendel showed that genes behave as particles that are not blended or changed during inheritance.

Answer 21

1900: Mendel’s previously published work on pea plants, which stated basic principles of inheritance, was rediscovered. 1902: Sutton proposed that genes are located on chromosomes. 1910: Thomas Hunt Morgan began studies of transmission genetics, using fruit fly mutants. 1930s: Fisher, Haldane, and Wright outlined the founding principles of population genetics. 1940s: Organization of chromosomes and genes were studied using bacteria and viruses. 1940s–1950s: Evidence was accumulated for DNA as the genetic material; Watson and Crick described the DNA structure. 1966: The relationship between chemical structure of DNA and amino acid sequence of proteins was determined. 1973: The first recombinant DNA experiments were conducted. 1977: The Gilbert and Sanger methods for DNA sequencing were published. 1986: Mullis developed PCR. 1990: The first use of gene therapy was used in humans. 1990s: The Human Genome Project was started. 1995: The first genome of a free-living organism was sequenced (Haemophilus influenzae). 1996: The first genome of a eukaryote was sequenced (yeast). 2000–present: The human genome sequence was released.

Answer 22

Techniques for the observation of cells have been available only since the late 1500s, when the first microscopes were produced. The observation of chromosomes has been possible for only a century and a half. The widespread systematic study of genes and inheritance has been conducted only in the twentieth century, since the rediscovery of Mendel's work in 1900. The structure of DNA was determined only in the mid-twentieth century. Many molecular genetic techniques, like PCR, have been developed only in the last few decades. However, without understanding the nature of chromosomes and genes, plant and animal breeders have been applying the principles of inheritance for thousands of years, to obtain desired characteristics in domesticated organisms.

Answer 23

Preformationism states that the egg or sperm carries a miniature adult, which would mean that all characteristics come from either the mother or father. Simple observation shows that offspring have traits from both parents.

Answer 24

This theory states that characteristics acquired during one's lifetime are passed to offspring. However, anatomical changes, like the loss of a limb, or the removal of a mouse's tail, are not seen in offspring.

Answer 25

Prokaryotic cells lack a nuclear membrane and possess no true membrane bounded cell organelles, whereas eukaryotic cells possess a nucleus and membrane bounded organelles such as chloroplasts and mitochondria.

Answer 26

This theory states that genetic information is mixed in an offspring and never separated. Some traits, however, disappear from one generation to the next, only to reappear in a subsequent generation.

Answer 27

Answers will vary, but the best answers will include one or more specific discoveries in genetics and describe how they affect the student personally. Examples could come from those listed in section 1.1 or from the students’ background knowledge. This question and Questions 52 and 53 will work best if students are asked to consider ahead of time how these discoveries might impact their lives. For example, students might discuss the role of genetics and genetic technology in the Green Revolution of the 1950s and 1960s, which greatly expanded food production throughout the world, making food more efficient, more affordable, and more available to world populations. A much smaller part of the world’s population work in agriculture, freeing up more people for work in other industries. They might also discuss the use of genetically modified crops in agriculture, including a significant proportion of corn and soybeans in the United States and other countries.

Answer 28

An example would be the use of genetic tests in medical practice. Genetic tests are already fairly commonplace and will become more common in the near future. In the future, most people will be offered one or more genetic tests as part of their ordinary medical care. They will need to understand the basis of the tests and their limitations, as well as how to interpret results and how to use the information provided.

Answer 29

Again, answers will vary, but an example is the possible abuse of genetic information about individuals that is becoming more available. Many people worry that results from genetic tests, for example, could be used to discriminate against individuals in the workplace and in the insurance marketplace. The Genetic Information Nondiscrimination Act offers limited protection against genetic discrimination, but the possibility of negative consequences from such tests remains.