,A corn gamete contains 10 chromosomes. (The leaf cells are diploid.)
FIGURE 1. 12
The horse populations have become adapted to their environment, which has changed over the course of
many years.
FIGURE 1.13
There are several possible examples of other model organisms, including rats and frogs.
End-of-chapter Questions:
Conceptual Questions
C1. A chromosome is a very long polymer of DNA. A gene is a specific sequence of DNA within that
polymer; the sequence of bases creates a gene and distinguishes it from other genes. Genes are
located in chromosomes, which are found within living cells.
C2. At the molecular level, a gene (a sequence of DNA) is first transcribed into RNA. The genetic code
within the RNA is used to synthesize a protein with a particular amino acid sequence. This second
process is called translation.
C3. A. Molecular level. This is a description of a how an allele affects protein function.
B. Cellular level. This is a description of how protein function affects cell structure.
C. Population level. This is a description of how the two alleles affect members of a population.
D. Organism level. This is a description of how the alleles affect the traits of an individual.
C4. Genetic variation is the occurrence of genetic differences within members of the same species or
different species. Within any population, variation may occur in the genetic material. Variation may
occur in particular genes, so some individuals carry one allele and other individuals carry a different
allele. Examples include differences in coat color among mammals or flower color in plants. At the
molecular level, this type of genetic variation is caused by changes in the DNA sequences of genes.
There may also be variation in chromosome structure and number.
C5. An extra chromosome (specifically an extra copy of chromosome 21) causes Down syndrome.
C6. You can pick almost any trait. For example, flower color in petunias would be an interesting choice.
Some petunias are red and others are purple. There must be different alleles in a flower color gene
that affect this trait in petunias. In addition, the amount of sunlight, fertilizer, and water also affects
the intensity of flower color.
C7. The term diploid means that a cell has two copies of each type of chromosome. In humans, nearly
all of the cells are diploid except for gametes (i.e., sperm and egg cells). Gametes usually have only
one set of chromosomes.
C8. A DNA sequence is a sequence of nucleotides. Each nucleotide may have one of four different
bases (i.e., A, T, G, or C). When speaking of a DNA sequence, the focus is on the sequence of those
bases.
C9. The genetic code is the way in which the sequence of bases in RNA is read to produce a sequence
of amino acids within a protein.
C10. A. A gene is a segment of DNA. For most genes, the expression of the gene results in the
production of a polypeptide, which is a unit of a protein. The functioning of proteins within living
cells largely determines the traits of an organism.
, B. A gene is a segment of DNA that usually encodes the information for the production of a specific
polypeptide. Genes are found within chromosomes. Many genes are found within a single
chromosome.
C. An allele is an alternative version of a particular gene. For example, suppose a plant has a flower
color gene. One allele could produce a white flower, while a different allele could produce an
orange flower. The white allele and orange allele are alleles of the flower color gene.
D. A DNA sequence is a sequence of bases, which are found within nucleotides. The information
within a DNA sequence (which is transcribed into an RNA sequence) specifies the amino acid
sequence within a polypeptide.
C11. The statement in part A is not correct. Individuals do not evolve. Populations evolve because
certain individuals are more likely to survive and reproduce and pass their genes to succeeding
generations.
C12. A. How genes and traits are transmitted from parents to offspring.
B. How the genetic material functions at the molecular and cellular levels.
C. Why genetic variation exists in populations, and how it changes over the course of many
generations.
Application and Experimental Questions
E1. There are many possible answers. Some common areas to discuss might involve the impact of
genetics in the production of new medicines, the diagnosis of diseases, the production of new kinds
of food, and the use of DNA fingerprinting to solve crimes.
E2. A genetic cross involves breeding two different individuals.
E3. This would be used to a great extent by molecular geneticists. The sequence of DNA is a molecular
characteristic of DNA. In addition, the sequence of DNA is interesting to transmission and
population geneticists as well.
E4. You would see 47 chromosomes instead of 46. There would be three copies of chromosome 21
instead of two copies.
E5. A. Transmission geneticists. Dog breeders are interested in how genetic crosses affect the traits of
dogs.
B. Molecular geneticists. This is a good model organism to study genetics at the molecular level.
C. Both transmission geneticists and molecular geneticists. Fruit flies are easy to cross and study the
transmission of genes and traits from parents to offspring. Molecular geneticists have also studied
many genes in fruit flies to see how they function at the molecular level.
D. Population geneticists. Most wild animals and plants would be the subject of population
geneticists. In the wild, you cannot make controlled crosses. But you can study genetic variation
within populations and try to understand its relationship to the environment.
E. Transmission geneticists. Agricultural breeders are interested in how genetic crosses affect the
outcome of traits.
E6. You need to follow the scientific method. You can take a look at an experiment in another chapter
to see how the scientific method is followed.
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