Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

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Sanders 3rd Edition

Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization

Problem 28d

Chapter 10, Problem 28d

A small population of deer living on an isolated island is separated for many generations from a mainland deer population. The populations retain the same number of chromosomes but hybrids are infertile. One chromosome (shown here) has a different banding pattern in the island population than in the mainland population.

Suppose that 40% of all meioses in mainland–island hybrids involve recombination somewhere in the chromosome region between q2.1 and p2. What proportion of the gametes of hybrid deer are viable? What is the cause of the decreased proportion of viable gametes in hybrids relative to the parental populations?

Verified step by step guidance

Understand the problem: The question involves hybrid infertility due to chromosomal differences between two populations of deer. The key is to analyze the recombination frequency and its impact on gamete viability.

Step 1: Recognize that the hybrid infertility is caused by structural differences in the chromosomes between the island and mainland populations. These differences can lead to improper pairing during meiosis, resulting in unbalanced gametes.

Step 2: Note that 40% of meioses involve recombination in the region between q2.1 and p2. Recombination in structurally different chromosomes can lead to duplications or deletions in the resulting gametes, making them non-viable.

Step 3: Calculate the proportion of viable gametes. If 40% of meioses involve recombination, then 60% of meioses do not involve recombination. Gametes from non-recombinant meioses are viable, while those from recombinant meioses are not.

Step 4: The decreased proportion of viable gametes in hybrids is due to the structural differences in the chromosomes. These differences disrupt proper alignment and segregation during meiosis, leading to unbalanced gametes in recombinant events.

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Key Concepts

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

Meiosis and Gamete Formation

Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in the formation of gametes (sperm and eggs). During meiosis, homologous chromosomes undergo recombination, where segments of DNA are exchanged, leading to genetic diversity. In the context of hybrids, understanding how meiosis operates is crucial, as it directly affects the viability of gametes produced by hybrid individuals.

Hybrid Incompatibility

Hybrid incompatibility occurs when two different species or populations interbreed, resulting in offspring that are often sterile or have reduced fitness. This can be due to genetic differences that disrupt normal development or reproductive processes. In the case of the deer populations, the infertility of hybrids suggests that genetic divergence has led to incompatibilities that affect gamete viability.

Chromosomal Banding Patterns

Chromosomal banding patterns are visual representations of chromosomes that highlight specific regions, allowing for the identification of structural differences between chromosomes from different populations. These differences can indicate genetic divergence and may contribute to reproductive barriers. In the scenario described, the distinct banding patterns between the island and mainland deer populations suggest evolutionary changes that could impact hybrid viability.

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Chromosome Structure

Related Practice

Textbook Question

Human chromosome 5 and the corresponding chromosomes from chimpanzee, gorilla, and orangutan are shown here. Describe any structural differences you see in the other primate chromosomes in relation to the human chromosome.

Textbook Question

A eukaryote with a diploid number of 2n=6 carries the chromosomes shown below and labeled (a) to (f).

Explain how you determined the correct alignment of homologous chromosomes on opposite sides of the metaphase plate.

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Textbook Question

A small population of deer living on an isolated island is separated for many generations from a mainland deer population. The populations retain the same number of chromosomes but hybrids are infertile. One chromosome (shown here) has a different banding pattern in the island population than in the mainland population.

In a mainland–island hybrid deer, recombination takes place in band q1 of the homologous chromosomes. Draw the gametes that result from this event.

Textbook Question

A eukaryote with a diploid number of 2n=6 carries the chromosomes shown below and labeled (a) to (f).

Carefully examine and redraw these chromosomes in any valid metaphase I alignment. Draw and label the metaphase plate, and label each chromosome with its assigned letter.

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Textbook Question

Draw the synapsis of these homologs during prophase I in hybrids produced from the cross of mainland with island deer.

Textbook Question

Describe how the banding pattern of the island population chromosome most likely evolved from the mainland chromosome. What term or terms describe the difference between these chromosomes?