Polyploidy PPT

# Introduction to Polyploidy ## What is Polyploidy? (Whole Genome Duplication; WGD) - More than a diploid set of chromosomes - **Allo vs auto** - How to identify polyploids? ## Ploidy - **Haploid (1N):** cells that contain one set of chromosomes. Which of human cells are haploid and what is 1N?...

# Introduction to Polyploidy ## What is Polyploidy? (Whole Genome Duplication; WGD) - More than a diploid set of chromosomes - **Allo vs auto** - How to identify polyploids? ## Ploidy - **Haploid (1N):** cells that contain one set of chromosomes. Which of human cells are haploid and what is 1N? - **Diploid (2N):** cells that contain two sets of chromosomes. Which of human cells are diploid and what is 2N? ## Differences between Diploid and Haploid - **Diploid (2n):** two copies of each chromosome. Three pairs of homologous chromosomes (of maternal and paternal origin). - **Haploid (n):** one copy of each chromosome. Three non-homologous chromosomes. ## Visual Representation of Ploidy - **Haploid:** one pair of chromosomes - **Diploid:** two pairs of chromosomes - **Polyploid:** more than two pairs of chromosomes ## Labeling Chromosomes - Use the following words to label the chromosomes: **triploid, haploid, tetraploid, diploid**. - **Core:** identify each set of chromosomes with the corresponding symbol: **4n, 3n, 2n, n** - **Challenge:** Suggest why an organism, created through the hybridization of a diploid and haploid genome, would be sterile. ## Diploid vs Haploid - **Body cells:** have the full set of chromosomes - they are **DIPLOID**, for example 46 chromosomes in humans. - **Sex cells:** (sperm and eggs) have half a set - they are **HAPLOID**, for example 23 chromosomes in humans. ## Types of Polyploidy - **Euploidy:** individual has one or more whole sets of chromosomes with each chromosome represented once in each set. There are three main kinds of euploidy: - **Haploidy:** individual with half (n=x) of the somatic cell chromosome number. - **Diploidy:** individual with two sets of the basic, complete genome (2n=2x). - **Polyploidy:** individual with more than two basic, complete sets of chromosomes in its somatic cells. Among polyploids, there are two main types: ## Diploid vs Haploid - **Diploid:** has pairs of chromosomes. - **Haploid:** has a single set of chromosomes. - **In humans:** diploid cells have 23 pairs of chromosomes. - **In humans:** haploid cells have 23 chromosomes (NO PAIRS). ## Types of Polyploids - **Autopolyploidy:** (genome doubling) of the same chromosome set. Autopolyploids are derived from within a single species. - **Allopolyploidy:** is the product of inter-specific hybridization and arises via hybridization between two species. An allopolyploid resulting due to chromosome doubling in a sterile hybrid derived from hybridization between two unrelated diploid species is also called as **"amphidiploid"**. If the parental species are polyploids, the derivative will be called as **"amphipolyploid"**. ## Polyploidy Summary - More than 2 whole sets of chromosomes, - **Autopolyploidy:** from the same genome, naturally occurring, or induced, often results in larger varieties, - **Allopolyploidy:** from different genomes, naturally occurring, or induced, often results in larger varieties, - **Autotriploids:** most often sterile, can produce beneficial traits. ## Autopolyploidy - Containing of multiple copies of the basic set (x) of chromosomes of the same genome. - **Karyotype of parent species:** meiotic error, self-fertilization; offspring with polyploid karyotypes may be viable and self-fertile. ## Allopolyploidy - A combination of genomes from different species. - **Species A:** meiotic error; chromosome number not reduced from 2n to n. - **Species B:** normal gamete. ## Autopolyploidy vs Allopolyploidy | Feature | Autopolyploidy | Allopolyploidy | |---|---|---| | Description | A type of polyploidy where the chromosome complement consists of more than two copies of homologous chromosomes. | A type of polyploidy where the chromosome complement consists of more than two copies of chromosomes derived from different species. | | Origin | Arises by the fusion of gametes of the same species. | Arises by the fusion of gametes of the different species. | | Chromosome sets | An autopolyploid cell contains homologous chromosome sets. | All chromosome sets of an allopolyploid cell are not homologous. | | Cause | Mainly caused by nondisjunction of chromosomes. | Caused by mating of different species. | | Meiosis | Does not undergo meiosis since it has arisen from one parent. | Can undergo meiosis. | | Examples | Seen in crops such as wheat, oats, sugar-cane, potato, peanut, banana, and coffee. | Seen in crops such as wheat and animals such as mules. | ## Characteristics of Allopolyploids - Larger cells - Vigorous plant - Less complex than autopolyploids - Recessive characters may appear less frequent ## Allopolyploids in Plant Breeding - Identify genetic origin of plant species - Produce new plant genotypes and plant species - Facilitate transfer of genes from related species - Facilitate transfer of individual chromosomes or pairs of chromosomes ## Example of Allopolyploid Hybridization - **Parents:** - **Raphanus:** 2n = 18 - **Brassica:** 2n = 18 - **Sterile F1 hybrid:** n+n = 9+9 = 2n = 18 - **Raphanobrassica:** (fertile amphidiploid) 2n+2n = 18+18 = 4n = 36 ## Formation of a Fertile Tetraploid Rabbage - **Raphanus (Radish):** 2n = 18, fertile - **Brassica (Cabbage):** 2n = 18, fertile - **Raphanobrassica (Rabbage):** 2n = 18, sterile (synaptic failure) - **Diploid (2n) Rabbage:** RRRRRRRRRR CCCCCCCCC - **Tetraploid (4n) Rabbage:** RRRRRRRRRR CCCCCCCCC RRRRRRRRRR CCCCCCCCC **The Formation Of A Fertile Tetraploid Rabbage:** - **R = radish chromosome** - **C = cabbage chromosome** ## Application of Allopolyploidy in Crop Improvement - **Bridging Cross:** Amphidiploids can be used as a bridge where direct cross between two species is not possible due to sterility in F1. - **Creation of New Crop Species:** Alloploidy sometimes helps in creation of new crop species, such as Triticale, Raphanobrassica, triploid (AAC), and tetraploids. - **Interspecific Gene Transfer:** In case of unavailability of the desirable characters within the species, they are transferred from the related species. - **Tracing the Origin of Crop Species:** Alloploidy study is used to identify the origin of natural alloploidy plants. ## Induction of Ploidy - **Natural Induction:** may arise from: - Unreduced gametes: chromosome number is not reduced during meiosis - Natural wide crossing following chromosome doubling - **Artificial Induction:** - Environmental Shock - **Chemical** - **Colchicine:** acts by dissociating the spindle and preventing migration of the daughter chromosomes to poles. It is applied to meristematic tissue, germinating seed, young seedling, root. Its action is modified or affected by temperature, concentration, and duration of treatment. ## Polyploidy Induction - **Use of colchicine:** (Alkaloid extracted from seeds of *Colchicum autumnale*). - **Colchicine disrupts normal chromosomal division:** Dissociates spindle preventing daughter chromosomes' migration to opposite poles, followed by mitosis - **Colchicine is applied to meristem regions of plants:** by wetting with aqueous solution. - **Effective when applied to germinating seeds:** to roots or developing meristems. ## Aneuploidy vs Polyploidy | Feature | Aneuploidy | Polyploidy | |---|---|---| | Description | The presence of an abnormal number of chromosomes. | The presence of more than two homologous chromosome sets. | | Frequency | More common in humans. | Rare in humans. | | Types | Nullisomy, Monosomy, disomy, trisomy and tetrasomy are the different types. | Triploid, Tetraploid, Hexaploid, Octaploid, Dodecaploid etc. are different types. | | Effects | Causes chromosomal disorders, some of them are lethal. | Triploid and tetraploid situations are lethal. | ## Classification of Polyploidy | Type of Polyploid | Definition/brief description | |---|---| | **Polyploidy** | A condition with more than two genomes | | **Autoployploidy** | 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** | A condition in which complete genomes of two or more species combine together. | | **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:** They occur spontaneously through the process of chromosome doubling - **Spontaneous chromosome doubling in ornamentals and forage grasses:** has led to increased vigor. - **Examples:** tulip, forage grasses, ryegrasses have yielded superior varieties following spontaneous chromosome doubling. ## Effect of Polyploidy - Increased fruit weight, fruit size, seed size, crop load, flower size etc. - Reduction in fertility (in odd ploidy level individuals) - Change in growth pattern. - Can be used to create higher diversity. - Greater ability to colonize new habitats than diploid ancestors. - Increase blooming period (marigold, Begonia, ageratum) ## Industrial Applications of Polyploidy - **Commercial synthesis of sex hormones and corticosteroids:** has been improved significantly by artificial induction of tetraploids from diploid *Dioscorea zingiberensis*, native to China . - **Other plants whose production of terpenes has increased:** following artificial chromosome doubling. It enhances production of secondary metabolites such as alkaloids and terpenes in polyploids. This may concurrently offer resistance to pests and pathogens. ## Polyploidy's Impact - **Polyploidy can make the...** - ...plant bigger - ... flowers bigger - ...fruits bigger - ...leaves bigger ## Example of Polyploidy's Impact on Plant Growth - **A:** Bolting time (days) of plants with different ploidy levels (2n, 4n, 6n, 8n). - **B:** Rosette area (cm2) of plants with different ploidy levels (2n, 4n, 6n, 8n). - **C:** Visual representation of plants with different ploidy levels (2n, 4n, 6n, 8n).