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Questions and Answers
What type of cells do humans have that contain two sets of chromosomes?
What defines an organism as a polyploid?
Which of the following describes allopolyploidy?
Which of the following statements is true about haploid cells?
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What is indicated by the term 'euploidy'?
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Which of the following is an example of autopolyploidy?
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What potential problem arises when a diploid and a haploid genome hybridize?
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What is the primary distinction between haploid and diploid cells?
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What term is used to describe an allopolyploid that results from chromosome doubling in a sterile hybrid derived from hybridization between two unrelated diploid species?
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What is the main characteristic of autopolyploidy?
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How does allopolyploidy primarily arise?
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What can be said about the chromosome sets in an allopolyploid cell?
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Which of the following is a key difference between autopolyploidy and allopolyploidy?
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In which scenario would a plant be classified as an amphipolyploid?
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What is a potential benefit of autotriploids?
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Which of the following crops is an example of an allopolyploid?
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What effect does colchicine have on chromosomal division?
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Which type of polyploidy involves the multiplication of a single genome?
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Which aneuploid condition describes the presence of only one copy of a chromosome?
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Which of the following is an effect of polyploidy?
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What is the difference in frequency between aneuploidy and polyploidy in humans?
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Which of the following types of polyploidy has two copies each of two distinct genomes?
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What is a common characteristic of aneuploid conditions?
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What is one of the methods used to induce polyploid plants?
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Which of the following is a characteristic of allopolyploids?
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What role do amphidiploids play in plant breeding?
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What is the chromosome configuration of the F1 hybrid in the example of allopolyploid hybridization?
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Which of the following examples illustrates the creation of a new crop species through allopolyploidy?
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What is the primary effect of colchicine in the induction of ploidy?
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What can natural induction of polyploidy result from?
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What does the formation of Raphanobrassica (Rabbage) indicate in terms of ploidy levels?
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What is the significance of tracing the origin of crop species in allopolyploidy studies?
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Study Notes
Polyploidy
- Polyploidy is a condition where an organism has more than two sets of chromosomes.
- Polyploidy can be allopolyploidy, which involves the combination of genomes from different species, or autopolyploidy, which involves the multiplication of the same genome.
- Polyploidy can be induced naturally or artificially.
Ploidy Levels
- Haploid (1N): Has one set of chromosomes; human sex cells are haploid (23 chromosomes).
- Diploid (2N): Has two sets of chromosomes; human body cells are diploid (46 chromosomes).
Differences between Diploid and Haploid
- Diploid: Contains two copies of each chromosome, with homologous pairs inherited from both parents.
- Haploid: Contains one copy of each chromosome, with no homologous pairs.
Labeling Chromosomes
- Haploid: n
- Diploid: 2n
- Triploid: 3n
- Tetraploid: 4n
Diploid vs Haploid (Humans)
- Body cells: Diploid (46 chromosomes)
- Sex cells (sperm and eggs): Haploid (23 chromosomes)
Types of Polyploidy
- Haploidy: Half the basic chromosome number (n=x).
- Diploidy: Two sets of the basic genome (2n=2x).
- Polyploidy: More than two sets of the basic genome.
Types of Polyploids
- Autopolyploids: Result from genome doubling within a single species.
- Allopolyploids: Result from hybridization between two different species.
Polyploidy Summary
- Autopolyploidy: Occurs from the same genome, resulting in naturally occurring or induced varieties with often larger sizes.
- Allopolyploidy: Occurs from different genomes, often resulting in naturally occurring or induced varieties with larger sizes.
- Autotriploids: Often sterile, but can have beneficial traits.
Autopolyploidy
- Contains multiple copies of the basic set of chromosomes (x) from the same genome.
- Karyotype of parent species: May arise from meiotic errors or self-fertilization, resulting in offspring with viable and self-fertile polyploid karyotypes.
Allopolyploidy
- Combination of genomes from different species.
- Species A: May have meiotic errors, leading to unreduced gametes (2n instead of n).
- Species B: Produces normal gametes.
Autopolyploidy vs Allopolyploidy
| Feature | Autopolyploidy | Allopolyploidy |
|---|---|---|
| Description | More than two copies of homologous chromosomes. | More than two copies of chromosomes derived from different species. |
| Origin | Fusion of gametes from the same species. | Fusion of gametes from different species. |
| Chromosome Sets | Homologous chromosome sets. | Not all chromosome sets are homologous. |
| Cause | Nondisjunction of chromosomes. | Mating of different species. |
| Meiosis | May not undergo meiosis due to one parent origin. | Can undergo meiosis. |
| Examples | Wheat, oats, sugar-cane, potato, peanut, banana, coffee. | Wheat, mules. |
Characteristics of Allopolyploids
- Larger cells: Larger cells with increased size.
- Vigorous plant: Increased vigor and growth rate.
- Less complex than autopolyploids: Often have a more stable genome with fewer complications.
- Recessive characters may appear less frequent: Due to multiple copies of the recessive gene present.
Allopolyploids in Plant Breeding
- Identify genetic origin of plant species: By analyzing polyploidy patterns.
- Produce new plant genotypes and plant species: Through hybridization and polyploidization.
- Facilitate transfer of genes from related species: To introduce desirable traits.
- Facilitate transfer of individual chromosomes or pairs of chromosomes: To create specific combinations of genetic material.
Example of Allopolyploid Hybridization
-
Parents:
- Raphanus (Radish): 2n = 18
- Brassica (Cabbage): 2n = 18
- Sterile F1 hybrid: 2n = 18 (due to unreduced gametes)
- Raphanobrassica (Rabbage): 4n = 36 (fertile amphidiploid)
Formation of a Fertile Tetraploid Rabbage
- Raphanus: 2n = 18 (fertile)
- Brassica: 2n = 18 (fertile)
-
Raphanobrassica: 2n = 18 (sterile)
- Diploid (2n) Rabbage: RRRRRRRRRR CCCCCCCCC
- Tetraploid (4n) Rabbage: RRRRRRRRRR CCCCCCCCC RRRRRRRRRR CCCCCCCCC
Application of Allopolyploidy in Crop Improvement
- Bridging Cross: Used to cross species that are normally incompatible.
- Creation of New Crop Species: Develop new hybrid varieties like Triticale, Raphanobrassica, etc.
- Interspecific Gene Transfer: Move desirable traits from related species.
- Tracing the Origin of Crop Species: Can help understand how polyploids evolved.
Induction of Ploidy
- Natural Induction: Spontaneous events like unreduced gametes and natural wide crossing.
-
Artificial Induction:
- Environmental Shock: Induced by environmental changes.
- Chemical: Use of agents like colchicine which disrupts spindle formation and prevents chromosome migration.
Polyploidy Induction
- Use of colchicine: Alkaloid extracted from Colchicum autumnale.
- Colchicine disrupts normal chromosomal division: Preventing daughter chromosomes from migrating to poles during mitosis.
- Colchicine is applied to meristem regions of plants: For targeted effects on cell division.
Aneuploidy vs Polyploidy
| Feature | Aneuploidy | Polyploidy |
|---|---|---|
| Description | Abnormal chromosome number. | More than two homologous sets of chromosomes. |
| Frequency | More common in humans. | Rare in humans. |
| Types | Monosomy, nullisomy, trisomy, tetrasomy. | Triploid, tetraploid, hexaploid, etc. |
| Effects | Chromosomal disorders, often lethal. | Lethal in triploid and tetraploid situations, but can be beneficial. |
Classification of Polyploidy
| Type of Polyploid | Definition |
|---|---|
| Polyploidy | More than two genomes present. |
| Autopolyploidy | Multiplication of the same genome. |
| Autotriploidy | Three copies of the same genome (3x) |
| Autotetraploidy | Four copies of the same genome (4x) |
| Autopentaploidy | Five copies of the same genome (5x) |
| Autohexaploidy | Six copies of the same genome (6x) |
| Allopolyploidy | Combination of genomes from two or more species. |
| Allotetraploidy | Two copies each of two distinct genomes (2x,+ 2x₂) |
| Allohexaploidy | Two copies each of three distinct genomes (2x,+ 2x₂ + 2x₃) |
| Allooctaploidy | Two copies each of four distinct species (2x,+ 2x₂ + 2x₃ + 2x₄) |
Classification of Aneuploids
| Term | Chromosome number |
|---|---|
| Monosomy | 2n-1 |
| Nullisomy | 2n-2 |
| Trisomy | 2n+2 |
| Tetrasomy | 2n+2 |
| Pentasomy | 2n+3 |
Inducing Polyploids
- Spontaneous occurrence: Can occur naturally.
- Spontaneous chromosome doubling in ornamentals and forage grasses: Can lead to more vigorous varieties.
Effect of Polyploidy
- Increased fruit weight, fruit size, seed size, crop load, flower size, etc. Larger fruits and seeds are common in polyploid plants.
- Reduction in fertility (in odd ploidy level individuals): Triploids often have reduced fertility.
- Change in growth pattern: Growth can be modified.
- Can be used to create higher diversity: Introduce new genetic variations.
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Description
Test your understanding of polyploidy and its significance in genetics. This quiz covers definitions, differences between haploid and diploid organisms, and chromosome labeling. See how well you grasp these essential concepts in biology!
