Chapter 4: Heredity and Reproduction
Mini Investigation: Variability—It’s a Coin Toss!
(Page 137)
A. Answers will vary with class data.
B. Answers will vary.
C. Answers will vary. The number of matching sequences will decrease with fewer students in the
class.
D. 8 = 256 sequences possible
E. 223 = 8 288 608 sequences possible
Section 4.1: The Nature of Heredity
Section 4.1 Questions
(Page 141)
1. (a) When organisms reproduce they pass genetic information on to their offspring. Heredity is the
passing on of characteristics from one generation to the next. The characteristics that are inherited
are determined by the genetic information that was passed on.
(b) Chromosomes are the structures inside the nucleus that carry genetic information. They are
made of DNA and proteins. It is the DNA carries the genetic information.
(c) A gene is part of a DNA molecule located on a chromosome. It can be thought of as an
individual piece or unit of genetic information.
(d) A cell that is diploid has two copies of each chromosome. A cell that is haploid has only one
copy of each chromosome.
2. Drawing should look similar to the sample shown here. There are 46 chromosomes in a single
human body cell.
Sample answer:
3. (a) (i) The diploid number of both lions and tigers is 38.
(ii) The diploid number of elephants is 56 and of woolly mammoths is (was) 58.
(iii) The diploid number of both chimpanzees and gorillas is 48.
(iv) The diploid number of both dogs and wolves is 78.
(v) The diploid number of wolves is 78 and of red foxes is 34.
(b) Most of these species in the pairs are very similar and so are their chromosome numbers. In
the case of dogs, they are a subspecies of wolves.
(c) Answers will vary, depending on how similar are the species chosen.
Sample answer:
The diploid number of kangaroos is 12, but the diploid number of moose is 40. The diploid
number of an alligator is 32 and the diploid number of a crocodile is 34. The kangaroo and moose
are not very similar, so it is not surprising that their diploid numbers are also very different.
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Chapter 4: Heredity and Reproduction
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Crocodiles and alligators are similar and so I expected that there chromosome numbers would also
be similar, which they are.
4.
5. The biological advantages of asexual reproduction include that only one individual is required and
there is no need to find a mate, to develop any special mating behaviours, or to produce
specialized sex cells. These are an advantage because reproduction can occur with less energy
expenditure and more efficiently. Asexual reproduction also produces offspring that are
genetically identical to parent. When the environment is stable and the parent is well-adapted to
that advantage, asexual reproduction gives the offspring a very good chance of being successful as
well.
6. The added costs of sexual reproduction include the energy and resources that must be used in the
generation and protection of sex cells, special characteristics involved in making sure the sex cells
unite, such as antlers, showy flowers, and mating behaviours. Some of these strategies or
behaviours also increase the chances that an individual will be predated.
7. The production of genetically identical offspring is a disadvantage when the environment is not
stable, and conditions can change rapidly. If all the individuals in a population in such an
environment are identical, it is less likely that they will have characteristics that help them to
survive under the changed conditions. A sexually reproducing population will have more genetic
variability, so there is a higher likelihood that at least some individuals will have traits that make
them suited to the new conditions.
8. (a) (i) Answers will vary, but are likely to include catastrophic events such as earthquakes,
tsunamis, fires, or mudslides.
(ii) Answers will vary, but are likely to include those associated with global warming, such
as increasing ocean water temperatures and loss of ice cover.
(b) In the case of sudden, rapid change, since species that reproduce sexually are more
genetically diverse, they are also likely to have at least a few individuals with characteristics that
are adapted to the new conditions. These individuals would then reproduce and the population as a
whole would be better adapted to the new conditions. A species that reproduced asexually would
be far less genetically diverse and therefore less likely to have characteristics that would allow
individuals to survive in the new conditions. The entire population might die out, as a result
In the case of a slow, gradual change, species that reproduce sexually would also be more
likely to have individuals that had traits more suited to the changes than would a species that
reproduced asexually. The sexually reproducing species would be more able to adapt to the
changes in the long term. The asexually-reproducing species might slowly become less adapted
and therefore slowly decline in numbers. However, since the changes are gradual, it would be less
likely that there would be a sudden mass die-out.
9. (a) The advantages of mating calls for birds is that they help an individual attract a mate and
therefore have more offspring. However, it takes energy to sing, leaves less time for finding food,
and it can be easier for predators to find a singing bird.
(b) The advantages of releasing chemical scents into the air by female moths is that it helps them
to attract a mate when they are ready to breed and therefore more offspring. However, making and
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Chapter 4: Heredity and Reproduction
4.1-2
releasing the chemicals requires energy and resources that could be used for survival, and wind
might carry the scent away, making it difficult for a mate to locate the female.
(c) The advantages of a male elephant seal being very large is that it shows potential mates that
the male is strong, healthy, and likely a good genetic risk. It also increases the chances that a male
can win the battles with other males over territory. Since all the females will mate only with the
one dominant male, the largest and strongest male will be the only one that can reproduce. The
disadvantage is that it takes a lot more energy and resources to grow to a large size and maintain
yourself, that fighting often causes injury, and that the winning male cannot leave the harem even
to feed or he will lose his advantage.
(d) The advantages of producing nectar is that it attracts more pollinating animals, which use the
nectar as food and transfer pollen to other flowers in the process. This gives the plants a better
chance of fertilization and therefore more offspring. The disadvantages are that it take energy and
resources to produce the nectar and that some animals will destroy the flower to get at the nectar,
rather than aid in pollination.
10. (a) Answers may vary.
Sample answer: The inherited markings on the body and wings of the butterfly may make it
easier for a butterfly of the same species to identify it and mate. It could help to camouflage the
butterfly so that it avoids predators more easily.
(b) Answers may vary.
Sample answer: Yes, this feature might help the butterfly to reproduce by helping it to attract a
mate or protecting it from being eaten before it gets a chance to reproduce.
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Chapter 4: Heredity and Reproduction
4.1-3