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Chapter 8: Problem 17

Explain why autopolyploids are usually sterile, whereas allopolyploids are often fertile.

Short Answer

Expert verified
Autopolyploids are sterile due to mispairing of identical chromosomes during meiosis, whereas allopolyploids have correct homolog pairing, making them fertile.

Step by step solution

01

Understanding Autopolyploids and Sterility

Autopolyploids result from the duplication of a single species' genome. This means that the organism has more than two sets of chromosomes, but all the chromosomes come from the same species. Because these chromosomes are homologous, they pair irregularly during meiosis, leading to unbalanced gametes. These gametes are often not viable, making autopolyploids usually sterile.
02

Defining Allopolyploids and Fertility

Allopolyploids arise from the combination of genomes from different species. This adds multiple sets of chromosomes from distinct species. During meiosis in allopolyploids, homologous chromosomes from each species can still pair up correctly, which allows for balanced gametes to be produced. As a result, allopolyploids are often fertile, since they can undergo normal reproductive processes.
03

Comparing Chromosome Pairing in Meiosis

In autopolyploids, the chromosomes struggle to find proper pairing partners due to their identical nature, causing mispairing and aneuploidy in gametes. In contrast, allopolyploids have differentiated chromosome sets that pair correctly with their respective homologs from the contributing species. This distinction in meiosis underlies why autopolyploids are generally sterile, while allopolyploids are fertile.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Autopolyploidy
Autopolyploidy occurs when an organism has more than two complete sets of chromosomes, all derived from a single species. This situation arises due to an error during cell division which causes a genome duplication. Humans, like many organisms, typically inherit two sets of chromosomes - one from each parent. However, autopolyploids possess multiples of these sets.

Imagine how a duplication error can lead to a genetic maze with too many paths. The similar chromosomes struggle during meiosis to form balanced sets due to their tendency to randomly pair with any of their kind. Each set seems indistinguishable from the other during chromosome pairing, leading to confusion.

  • Since all chromosomes are from the same species, they are essentially homologous.
  • This results in irregular pairing and unbalanced gametes.
  • Unbalanced gametes rarely succeed in fertilization, leading to sterility commonly seen in autopolyploids.
Allopolyploidy
Allopolyploidy describes when an organism possesses multiple sets of chromosomes sourced from different species. This happens when two different species crossbreed and the resultant hybrid undergoes chromosome doubling.

The intriguing aspect of allopolyploidy is that it blends genetic material from distinct species, broadening the range of genetic variation. Unlike autopolyploids, allopolyploids have a structured way of maintaining harmony.
  • The chromosomes from one species have distinct homologous pairs from the other species.
  • This structured pairing during meiosis ensures that gametes contain balanced sets of chromosomes.
  • Consequently, allopolyploids often retain fertility, allowing them to reproduce and pass on their genetic diversity.
Chromosome Pairing
Chromosome pairing is a critical stage during meiosis where chromosomes line up with their homologous partners to ensure correct genetic division.

In both autopolyploids and allopolyploids, chromosome pairing plays a pivotal role, yet it unfolds in dramatically different ways due to the source of the chromosomes.
  • In autopolyploids, similar chromosomes compete for pairing, leading to an unbalanced distribution.
  • Allopolyploids, however, have clear distinction in chromosome sets, easing the pairing process.
  • Proper pairing directly impacts the viability of produced gametes and ultimately, the fertility of the organism.
Meiosis
Meiosis is the process of cell division which reduces the chromosome number by half in gametes. It's crucial for sexual reproduction, providing genetic diversity.

In the realm of polyploidy, meiosis is where the difference between autopolyploids and allopolyploids becomes starkly evident.
  • For autopolyploids, irregular pairing during meiosis culminates in gametes with uneven chromosome numbers, often leading to sterility.
  • Allopolyploids, on the other hand, tend to navigate meiosis with efficiency, producing balanced gametes through correct pairing of differentiated genomes.
  • This efficiency allows allopolyploids to thrive and reproduce successfully, which contributes to their wide use in agriculture as fertile crops.

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Most popular questions from this chapter

Humans and many other complex organ isms are diploid, possessing two sets of genes, one inherited from the mother and one from the father. However, a number of eukaryotic organ isms spend most of their life cycles in a haploid state. Many of these eukaryotes, such as Neurospora and yeast, still undergo meiosis and sexual reproduction, but most of the cells that make up the organism are haploid. Considering that haploid organ isms are fully capable of sexual reproduction and generating genetic variation, why are most complex cukaryotes diploid? In other words, what might be the evolutionary advantage of existing in a diploid state instead of a haploid state? And why might a few organisms, such as Neurospona and yeast, exist as haploids?

The green-nose fly normally has six chromosomes: two metacentric and four acrocentric. A geneticist examines the chromosomes of an odd-looking green- nose fly and discovers that it has only five chromosomes; three of them are metacentric and two are acrocentric. Explain how this change in chromosome number might have taken place.

What is uniparentaldisomy and how does it arise?

What is haploinsufficiency?

The Notch mutation is a deletion on the X chromosome of Dmsophila melanogaster. Female flies heterozygous for Notch have an indentation on the margins of their wings; Notch is lethal in the homozygous and hemizygous conditions. The Notch deletion covers the region of the X chromosome that contains the locus for white eyes, an X-linked recessive trait. Give the phenotypes and proportions of progeny produced in the following crosses. a. A red-eyed, Notch female is mated with a white-eyed male. b. A white-eyed, Notch female is mated with a red-eyed male. c. A white-eyed, Notch female is mated with a white-eyed male.
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