1. Which diagram best illustrates the processes of DNA replication, meiosis, and separation of sister chromatids?

Transcription

1 1. Which diagram best illustrates the processes of DNA replication, meiosis, and separation of sister chromatids? (A) This answer suggests the student may understand that meiosis involves the splitting of homologous chromosomes, but does not understand that the first step in this process is the replication of all chromosomes to create a pair of two chromatids attached by a centromere (the X-shaped structures), and that the last step is the separation of sister chromatids in meiosis II to create four daughter cells, each containing a long chromosome and a short chromosome. (B) This answer suggests the student may understand that meiosis involves the replication of all chromosomes and the pairing up and separation of homologous chromosomes, but does not understand that the final step in this process is the separation of sister chromatids in meiosis II to produce four haploid daughter cells, each with the haploid number of chromosomes. (C) Page 1 of 8

2 This answer suggests the student may understand that meiosis involves the replication of all chromosomes and the separation of sister chromatids, but does not realize that the first division involves the pairing up and separation of homologous chromosomes, and that this is then followed by a second division that produces four daughter cells, each with the haploid number of chromosomes. (D) Rationale: This answer suggests the student understands that the representation accurately depicts how the process of meiosis produces four haploid cells from one diploid parent cell: the formation of chromosomes, formation of the spindle complex, pairing of homologs, lining up of homologs on the equator, migration of chromosomes, and two divisions. The student understands that the representation shows the major events of meiosis in the correct order to form gametes that will accurately transmit heritable information from parent to offspring following fertilization. Aligned to: LO 3.11 CA 3.11: Evaluate DNA Transmission Data 2. Which diagram best shows the steps and the correct sequence of changes in ploidy that chromosomes undergo while being transmitted from parent to offspring when a zygote is produced? (A) Page 2 of 8

3 Rationale: This answer suggests the student understands how the processes in meiosis followed by fertilization ensure the accurate transmission of heritable information from parent to offspring, in that meiosis I reduces the chromosome number from diploid to haploid (2n n) and that fertilization restores the chromosome number to produce a diploid zygote (2n) when two gametes combine. (B) This answer suggests the student may understand that the original diploid chromosome number is maintained during mitosis and reduced by one half during meiosis I, but does not understand that fertilization is required following meiosis II to restore the chromosome number to 2n. The student may not understand that the end products of meiosis are haploid gametes (n), and that it is during sexual reproduction and fertilization that two gametes combine and a diploid zygote (2n) is produced. (C) This answer suggests the student may understand that meiosis reduces the number of chromosomes in a cell from the diploid number to the haploid number and that the diploid number is restored to produce a zygote, but does not understand that meiosis I, not meiosis II, reduces the chromosome number from diploid to haploid (2n n), and that fertilization, not mitosis, is required following meiosis to produce a diploid zygote. The student may not understand that the end products of meiosis are haploid gametes (n), and that it is during sexual reproduction and fertilization that two gametes combine and a diploid zygote (2n) is produced. (D) Page 3 of 8

4 This answer suggests the student may understand that meiosis I reduces the chromosome number from diploid to haploid (2n n) and that the diploid number is restored to produce a zygote, but does not understand that fertilization entails the combination of two haploid cells (gametes) to produce a diploid zygote. The student may not understand that it is during sexual reproduction and fertilization that two gametes combine and a diploid zygote (2n) is produced. Aligned to: LO 3.11 CA 3.11: Evaluate DNA Transmission Data 3. The diagram below shows the meiotic divisions involved in the formation of an egg cell (oogenesis). The polar bodies produced during oogenesis eventually degenerate. Which is the best explanation of the role of polar bodies during the formation of an egg? (A) The first polar body is produced by removal of the Y chromosome to ensure that an egg contains only an X chromosome. In meiosis II, the extra set of chromosomes is placed into the second polar body so that the egg has the proper number of chromosomes. Page 4 of 8

5 This answer suggests the student may understand that polar bodies allow for the number of chromosomes to be reduced with each cell division, but does not understand that the first polar body, not the Y chromosome (since a female would not have a Y chromosome), removes one set of homologous chromosomes during the first meiotic division, because the student does not understand the importance of the first meiotic division in producing haploid cells (gametes). (B) The first polar body is generated in meiosis I, when all of the chromosomes are passed on to the egg, allowing for cell division without a reduction in chromosomes. In meiosis II, the sister chromatids are separated into two cells and result in a second polar body containing the extra chromatid set. This answer suggests the student may understand that polar bodies allow for the number of chromosomes to be reduced, but does not understand that the first polar body removes one set of homologous chromosomes (not sister chromatids) during the first meiotic division, because the student does not understand the importance of the first meiotic division in producing haploid cells (gametes). (C) The first polar body is generated in meiosis I, when the extra set of chromosomes is removed to ensure that the secondary oocyte has the diploid number. In the second meiotic division, the second polar body is created to produce an egg with the haploid number of chromosomes. This answer suggests the student may understand that polar bodies allow for the number of chromosomes to be reduced with each cell division, but does not understand that in meiosis I, the homologous chromosomes are split to produce a haploid secondary oocyte, because the student does not understand the importance of the first meiotic division in producing haploid cells (gametes). (D) The first polar body is produced in meiosis I, when the pairs of homologous chromosomes are separated into two cells. In meiosis II, the second polar body is generated when sister chromatids are separated into two cells to obtain the haploid number of chromosomes in the egg. Page 5 of 8

6 Rationale: This answer suggests the student understands that a polar body is created in meiosis I to produce a haploid secondary oocyte and that the second polar body is created in meiosis II, when sister chromatids separate to ultimately produce an egg (gamete) with the proper number of chromosomes (n). The student understands that in order to produce a gamete that can accurately transmit heritable information to an offspring during fertilization, the gamete must be haploid, so the first polar body is produced in meiosis I when homologous chromosomes separate, and in meiosis II, the second polar body is generated when sister chromatids separate. (Unlike in the generation of male gametes, it is common for a single female gamete to be produced at the end of meiosis due to the need to retain much of the parent cell s cytoplasm in the produced egg.) Aligned to: LO 3.11 CA 3.11: Evaluate DNA Transmission Data 4. A genetic marker is a gene (DNA sequence) with a known location and a somewhat predictable inheritance pattern. The inheritance of a genetic condition located on the Y sex chromosome is indicated by Y on the pedigree below. Because the condition results from a unique sequence of nucleotides that is extremely rare in the human population, it is often used in paternity cases to determine if offspring are related to the potential parents. Which statement best explains how using a genetic marker on the Y chromosome is more helpful than using markers on other chromosomes in determining paternity over many generations? (A) Markers on other chromosomes in the body would be less useful for determining paternity, because the chromosomes exist in homologous pairs after fertilization, and many recessive genes will not be expressed in the offspring. Page 6 of 8

7 This answer suggests the student may understand that recessive traits can be difficult to trace in families since carriers do not show the trait, but does not understand that this would not be an issue with a genetic marker because markers are traced using molecular biology techniques, and even if a recessive trait were not expressed in an individual s phenotype, it would still be present on the individual s chromosome and detected during analysis. In addition, only 50% of a parent s autosomes are passed on to offspring due to segregation during meiosis I, but every Y chromosome is passed from father to son, so genetic markers on the Y chromosome will always be passed on. (B) Markers on other chromosomes in the body would be less useful for determining paternity, because the chromosomes exist as tetrads before meiosis, and it is very difficult to find a genetic marker among four chromatids. This answer suggests the student may understand that autosomal chromosomes exist as tetrads during meiosis, but does not understand that this does not disrupt genetic screening since these tests are performed on diploid body cells, not cells about to undergo meiosis. In addition, only 50% of a parent s autosomes are passed on to offspring due to segregation during meiosis, but every Y chromosome is passed from father to son, so genetic markers on the Y chromosome will always be passed on. (C) Markers on other chromosomes in the body would be less useful for determining paternity, because autosomal genetic markers are very difficult to identify compared to those that are sex-linked, since there are so many more autosomal chromosomes than sex chromosomes. This answer suggests the student may understand that there are many more autosomal chromosomes than sex chromosomes in humans, but does not understand that this would not be an issue with a genetic marker because markers are traced using molecular biology techniques that can easily locate the marker on a specific chromosome. In addition, only 50% of a parent s autosomes are passed on to offspring due to segregation during meiosis, whereas the Y chromosome is always passed from father to son, so genetic markers on the Y chromosome can be used to trace paternity. (D) Markers on other chromosomes in the body would be less useful for determining paternity, because during meiosis there is only a 50% chance that they will be passed on to a child, but the Y chromosome will be passed on to all male offspring. Page 7 of 8

8 Rationale: This answer suggests the student understands that homologous chromosomes are separated during meiosis, so only 50% of autosomes will be passed to any particular offspring, and that the Y chromosome will always be passed on to all male offspring, so a genetic marker on the Y chromosome is therefore most useful in determining paternity over many generations. Aligned to: LO 3.11 CA 3.11: Evaluate DNA Transmission Data Page 8 of 8