DBQ on p. 138 – February 6, 2013
1)
a) In figure 9, distinguish between:
i) chromosome 5 and chromosome 6
Chromosome 5
ii) chromosome 17 and chromosome 18
Chromosome 18 has a thicker yellow tip than chromosome 17.
Chromosome 18 also has a white band at the other end whereas chromosome 17
doesn’t.
iii) the X and Y chromosome
The X chromosome is larger than the Y chromosome.
2)
a) State the gender of the subject of the human karyotype in Figure 9.
Female.
b) State whether the karyotype shows any abnormalities.
DBQ on p. 137 – February 6, 2013
1) Outline the relationship between maternal age and the incidence of chromosomal
abnormalities in live births.
There is an exponential relationship between maternal age and the incidence of
chromosomal abnormalities in live births; as maternal age increases, incidence
increase at an accelerating rate.
2)
a) For mothers 40 years of age, determine the probability that they will give
birth to a child with trisomy 21.
The probability is approximately 1%.
b) Using the data in Figure 5, calculate the probability that a mother of 40
years of age will give birth to a child with a chromosomal abnormality other than
trisomy 21.
The probability is approximately 0.8%.
3) Only a small number of possible chromosomal abnormalities are ever found among
live births, and trisomy 21 is much the commonest. Suggest reasons for these trends.
If there is an abnormality in chromosomes 1 to 12, spontaneous abortion always
occurs. Furthermore, the mother can undergo prenatal tests to identify whether or not
the embryo has chromosomal abnormalities, and if so, choose to abort it.
4) Discuss the risks parents face when choosing to postpone having children.
When parents choose to postpone having children, they increase the risks of their
children having chromosomal abnormalities. As the mother gets older than 40 years,
the chances of her baby having an abnormality increases rapidly.
DBQ on p. 136 – February 4, 2013
1) Compare the DNA content of the bog mosses.
The S. aongstroemii, S. balticum, S. fibriatum, S. teres, S. tundrae, and S. warnstorfii all
have 19 chromosomes and masses ranging from 0.42 to 0.48 DNA/pg.
2) Suggest a reason for six of the species of bog moss on the Svalbard islands all
having the same number of chromosomes in their nuclei.
A reason why the six species of bog moss on the Svalbard islands all had the same
number of chromosomes could be because they all live in the same environment.
3) S. arcticum and S. olafii probably arose as new species when meiosis failed to occur
in one their ancestors.
a) Deduce the chromosome number of nuclei in their leaf cells. Give two
reasons for your answer.
The chromosomes number of nuclei in their leaf cells is 38 because if meiosis
failed to occur then there would be twice as many chromosomes and also because the
mass of the DNA for those two species is approximately double the masses of the
other species (with 19 chromosomes).
b) Suggest a disadvantage to S. arcticum and S. olafii of having more DNA
than other bog mosses.
A disadvantage could be that there would be increased chances of a mutation
occurring because there are more possibilities for error.
4) It is unusual for plants and animals to have an odd number of chromosomes in their
nuclei. Explain how mosses can have odd numbers of chromosomes in their leaf cells.
Mosses can have odd numbers of chromosomes in their leaf cells because they have a
haploid number of chromosomes.
DBQ on p. 134 – February 4, 2013
1) Outline five similarities between the life cycle of a moss and of a human.
Both involve bitosis, meiosis, and fertilization. Both also have eggs, sperm, and
zygotes.
2) Distinguish between the life cycles of a moss and a human by giving five
differences.
The human life cycle has a male and female but moss doesn’t. Human cycles are two
cycles (female and male) that meet together but moss is just one cycle. Meiosis
happens twice in the human cycle but only once in the moss cycle, and mitosis
happens four times in the moss cycle but only twice in the human cycle. Moss plants
have a haploid number of chromosomes whereas humans have a diploid number.
DBQ on p. 145 – January 30, 2013
1) There are many different chromosome numbers in the table, but some numbers are
missing, for example, 5, 7, 11, 13. Explain why none of the species has 13
chromosomes.
None of the species have 13 chromosomes because in the body cells of most
eukaryotes there are two chromosomes of each type.
2) Discuss, using the data in the table, the hypothesis that the more complex an
organism is, the more chromosomes it has.
The data shown in the table seems to support this hypothesis up to a certain point
because in general, larger mammals have more chromosomes than insects. It’s
assumed that larger mammals are more complex than insects, so this makes sense.
However, there are exceptions because organisms that are thought to be the most
intelligent (i.e. modern humans and chimpanzees) have fewer chromosomes than
those that aren’t considered to be as intelligent (i.e. domestic sheep and goats).
3) Explain why the size of the genome of a species cannot be deduced from the
number of chromosomes.
The number of chromosomes doesn’t reveal the size of the whole of the genetic
information of an organism.
4) Suggest, using the data in Table 3, a change in chromosome structure that may have
occurred during human evolution.
Humans may have lost some of their chromosomes.