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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 23
Chapter 2, Problem 23

You are given a metaphase chromosome preparation (a slide) from an unknown organism that contains 12 chromosomes. Two that are clearly smaller than the rest appear identical in length and centromere placement. Describe all that you can about these chromosomes.

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Step 1: Identify the total chromosome number and note the presence of two smaller chromosomes that are identical in length and centromere position. This suggests these two chromosomes may be homologous pairs or possibly sex chromosomes if the organism is diploid.
Step 2: Understand that chromosomes identical in length and centromere placement are likely homologous chromosomes, meaning they carry the same genes but may have different alleles. This is typical in diploid organisms where chromosomes come in pairs.
Step 3: Consider the significance of the smaller size of these two chromosomes compared to the others. Smaller chromosomes may carry fewer genes or represent specialized chromosomes such as sex chromosomes or microchromosomes, depending on the organism.
Step 4: Recognize that the centromere placement (metacentric, submetacentric, acrocentric, or telocentric) helps classify chromosome morphology, which can be used to identify chromosome pairs and understand their behavior during cell division.
Step 5: Conclude that from the metaphase spread, you can describe the chromosome number (12), the presence of a pair of smaller homologous chromosomes, their morphology based on centromere position, and hypothesize about their genetic significance, but further analysis (e.g., banding patterns or molecular markers) would be needed for detailed identification.

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Key Concepts

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

Chromosome Structure and Morphology

Chromosomes are composed of DNA and proteins, with distinct regions such as the centromere that influence their shape. The position of the centromere classifies chromosomes as metacentric, submetacentric, or acrocentric, which helps in identifying and comparing chromosomes based on size and shape.
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Homologous Chromosomes and Chromosome Pairs

In diploid organisms, chromosomes exist in homologous pairs, each inherited from one parent. Identical length and centromere placement suggest the two smaller chromosomes are homologs, meaning they carry the same genes but may have different alleles.
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Karyotyping and Chromosome Identification

Karyotyping involves arranging chromosomes by size and centromere position to analyze chromosome number and structure. Observing 12 chromosomes with two smaller identical ones allows inference about the organism’s chromosome count, potential sex chromosomes, or presence of autosomes.
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Related Practice
Textbook Question

The nuclear DNA content of a single sperm cell in Drosophila melanogaster is approximately 0.18 picogram. What would be the expected nuclear DNA content of a primary spermatocyte in Drosophila? What would be the expected nuclear DNA content of a somatic cell (non-sex cell) in the G1 phase? What would be the expected nuclear DNA content of a somatic cell at metaphase?

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Textbook Question

Contrast the chromatin fiber with the mitotic chromosome. How are the two structures related?

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Textbook Question

Describe the 'folded-fiber' model of the mitotic chromosome.

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Textbook Question

If one follows 50 primary oocytes in an animal through their various stages of oogenesis, how many secondary oocytes would be formed? How many first polar bodies would be formed? How many ootids would be formed? If one follows 50 primary spermatocytes in an animal through their various stages of spermatogenesis, how many secondary spermatocytes would be formed? How many spermatids would be formed?

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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.

In mitosis, what chromatid combination(s) will be present during metaphase? What combination(s) will be present at each pole at the completion of anaphase?

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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.

During meiosis I, assuming no crossing over, what chromatid combination(s) will be present at the completion of prophase I? Draw all possible alignments of chromatids as migration begins during early anaphase.

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