Question

1) Single-celled organisms, like amoebas, reproduce by mitosis. Explain how the genetic makeup of these organisms differs from organisms that undergo meiosis.

a) Organisms reproducing through mitosis produce genetically different daughter cells whereas those producing through meiosis have genetically identical daughter cells.
b) Crossing over or mixing of chromosomes does not occur in meiosis whereas it is prevalent in mitosis.
c) Mitosis is a process of asexual reproduction in which the number of chromosomes are reduced by half producing two haploid cells whereas in meiosis two diploid cells are produced by cell division.
d) Organisms producing through mitosis create genetically identical offspring as only a single parent copies its entire genetic material to the offspring. In meiosis, two parents produces gametes and the offspring have only half the number of chromosomes of each parent and hence genetic variation is introduced.

2) Human males typically have XY chromosomes and females have XX chromosomes, but there are rare instances in which a male can inherit an XXY or an XYY, or a female can have three X chromosomes. Explain how an error in meiosis can cause these aberrations.

a) Errors can arise only during the recombination process which may result in deletions, duplications or translocations causing such abnormalities.
b) Aberrations caused when a pair of homologous chromosomes fails to separate during anaphase I or when sister chromatids fail to separate during anaphase II, the daughter cells will inherit unequal numbers of chromosomes.
c) Errors during anaphase I of meiosis only cause such aberrations resulting in unequal numbers of chromosomes.
d) Errors during meiosis introduce variations in the DNA sequence, which depends specifically on the size of the variant only.

3) Though the stages of meiosis have the same names as the stages of mitosis, they exhibit fundamental differences. What are the main differences between the two processes?

a) Meiosis differs from mitosis in that the number of chromosomes is halved and genetic variation is introduced in meiosis, but not in mitosis.
b) Meiosis differs from mitosis in that the number of chromosomes is halved and genetic variation is reduced in meiosis, but not in mitosis.
c) Metaphase and telophase portions of meiosis and mitosis are the same. Meiosis and mitosis are also the same, except for the number of chromosomes. Anaphase I and anaphase are different.
d) Prophase and telophase portions of meiosis and mitosis are the same. Meiosis II and mitosis are also the same and have the same number of chromosomes. Anaphase I and anaphase are different.

4) Explain why meiosis might be considered a special case of mitosis.

a) Meiosis simply repeats each step of mitosis two times.
b) Meiosis is essentially the same as mitosis except it occurs only in the gonads.
c) Meiosis and mitosis use similar mechanisms in the same sequence of steps.
d) Meiosis and mitosis follow the same steps but in slightly different order.

5) Cells enter meiosis after going through an S-phase of their life cycle, so the chromosomes have been duplicated. In order to produce reproductive cells, however, the number needs to be cut in half. How does meiosis accomplish this goal?

a) Meiosis produces haploid cells because only half of the DNA is replicated in the S-phase preceding meiosis I.
b) Meiosis reduces the chromosome number in the first division and then restores the number in the second division.
c) Chromosome number is halved during the interphase between meiosis I and meiosis II.
d) Chromosome number is halved during meiosis I when the homologous chromosomes separate, but the sister chromatids remain connected.

Answer 1

Ans.1. The organism that reproduces via meiosis is genetically different than its parents.
Mitosis produces a clone of the parent as an offspring whereas in meiosis, genetic recombination is involved and hence variation is present. So correct option is (d)

Ans. 2. This kind of chromosomal aberrations in which an extra copy of a chromosome is present or absent is called aneuploidy. It occurs due to non-disjunction of chromosomes/chromatids at anaphase stages of cell cycle.
So the answer is (b)

Ans.3. The fundamental difference is; (a) Meiosis differs from mitosis in that the number of chromosomes is halved and genetic variation is introduced in meiosis, but not in mitosis.


Ans 4. Meiosis can be considered a special case of Mitosis because (c) Meiosis and mitosis use similar mechanisms in the same sequence of steps.


Ans. 5. Meiosis halves the no of the chromosomes by separating the homologous pair of chromosomes in Meiosis I and subsequently separating the sister chromatids of a chromosome in Meiosis II. The correct option is (d).