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Ch. 2 - Mitosis and Meiosis
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 2 - Mitosis and MeiosisProblem 31a
Chapter 2, Problem 31a

A species of cereal rye (Secale cereale) has a chromosome number of 14, while a species of Canadian wild rye (Elymus canadensis) has a chromosome number of 28. Sterile hybrids can be produced by crossing Secale with Elymus.
What would be the expected chromosome number in the somatic cells of the hybrids?

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1
Determine the haploid chromosome number (n) for each parent species. For Secale cereale, the diploid chromosome number is 14, so the haploid number is n = 14 / 2 = 7. For Elymus canadensis, the diploid chromosome number is 28, so the haploid number is n = 28 / 2 = 14.
Understand that hybrids are formed by combining the haploid gametes (n) from each parent species. This means the hybrid will inherit 7 chromosomes from Secale cereale and 14 chromosomes from Elymus canadensis.
Add the haploid chromosome numbers from both parent species to calculate the total chromosome number in the hybrid. This is given by: Total chromosomes = n(Secale) + n(Elymus).
Recognize that the resulting hybrid is sterile because the chromosomes from the two species are not homologous and cannot pair properly during meiosis, leading to infertility.
Conclude that the somatic (diploid) cells of the hybrid will contain the combined chromosome number from both parent species, which is the sum of their haploid numbers.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Chromosome Number

Chromosome number refers to the total count of chromosomes in a cell, which is crucial for understanding genetic inheritance. In this case, Secale cereale has 14 chromosomes, while Elymus canadensis has 28. The chromosome number is significant because it determines the genetic makeup and potential for hybridization between species.
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Hybridization

Hybridization is the process of crossing two different species or varieties to produce a hybrid. In this scenario, the sterile hybrids produced from Secale and Elymus indicate that while they can mate, the resulting offspring may not be fertile due to differences in chromosome number, which can disrupt normal meiosis.
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Somatic Cells

Somatic cells are any cells forming the body of an organism, excluding germ cells involved in reproduction. The expected chromosome number in the somatic cells of the hybrids would typically be the sum of the parental chromosome numbers, but in this case, the hybrids are sterile, indicating that they may not have a stable chromosome number, often leading to an intermediate or aneuploid condition.
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Related Practice
Textbook Question

Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., Am and Ap). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis.

Draw all possible combinations of chromatids during the early phases of anaphase in meiosis II.

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Textbook Question

Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., Am and Ap). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis.

Assume that during meiosis I none of the C chromosomes disjoin at metaphase, but they separate into dyads (instead of monads) during meiosis II. How would this change the alignments that you constructed during the anaphase stages in meiosis I and II? Draw them.

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Textbook Question

Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., Am and Ap). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis.

Assume that each gamete resulting from Problem 29 fuses, in fertilization, with a normal haploid gamete. What combinations will result? What percentage of zygotes will be diploid, containing one paternal and one maternal member of each chromosome pair?

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Textbook Question

A species of cereal rye (Secale cereale) has a chromosome number of 14, while a species of Canadian wild rye (Elymus canadensis) has a chromosome number of 28. Sterile hybrids can be produced by crossing Secale with Elymus.

Given that none of the chromosomes pair at meiosis I in the sterile hybrid (Hang and Franckowlak, 1984), speculate on the anaphase I separation patterns of these chromosomes.

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Textbook Question

An interesting procedure has been applied for assessing the chromosomal balance of potential secondary oocytes for use in human in vitro fertilization. Using fluorescence in situ hybridization (FISH), Kuliev and Verlinsky (2004) were able to identify individual chromosomes in first polar bodies and thereby infer the chromosomal makeup of 'sister' oocytes. Assume that when examining a first polar body you saw that it had one copy (dyad) of each chromosome but two dyads of chromosome 21. What would you expect to be the chromosomal 21 complement in the secondary oocyte? What consequences are likely in the resulting zygote, if the secondary oocyte was fertilized?

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Textbook Question

Assume that you were examining a first polar body and noted that it had one copy (dyad) of each chromosome except chromosome 21. Chromosome 21 was completely absent. What would you expect to be the chromosome 21 complement (only with respect to chromosome 21) in the secondary oocyte? What consequences are likely in the resulting zygote if the secondary oocyte was fertilized?

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