Polyploidy Explained

# Introduction - 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 - 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 haploid and what is 2N = ? # Differences between Diploid and Haploid | Diploid (2n) | Haploid (n) | | :--------------------------------------- | :------------------------------------------- | | Two copies of each chromosome | One copy of each chromosome | | Three pairs of homologous chromosomes | Three non-homologous chromosomes | | (of maternal and paternal origin) | | # Haploid, Diploid and Polyploid Chromosomes - The image shows three different types of chromosomes. - **Haploid:** one set of chromosomes. - **Diploid:** two sets of chromosomes. - **Polyploid:** more than two sets of chromosomes. # Identifying Polyploidy - **Core:** identify each set of chromosomes with the corresponding symbol: 4n, 3n, 2n, n - **Challenge:** Suggest why an organism, created through the hybridisation of a diploid and haploid genome, would be sterile. # Diploid vs Haploid | Diploid (2n) | Haploid (n) | | :------------------------------ | :-------------------------------- | | Two sets of chromosomes | One set of chromosomes | | Body cells have the full set | Sex cells (sperm and eggs) have half a set | | DIPLOID (In humans, 46) | HAPLOID (In humans, 23) | | Diploid = 4 | Haploid = 2 | # 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. - allopolyploids arise via hybridization between two species. # Autotriploidy - 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. <start_of_image>- **Containing of multiple copies of the basic set (x) of chromosomes of the same genome.** - **Karyotype of parent species:** The image shows a diagram of meiosis, where the chromosomes are duplicated and then separated. - The normal chromosomes are shown in the blue set. - The unreduced gametes are - The zygote (autopolyploid) is shown in the pink, yellow and blue set. - **2n = 6** - In the next set of chromosomes, the unreduced gamete is shown in the blue set; the zygote (autopolyploid) is shown in the pink set; and the offspring with polyploid karyotypes are shown in the yellow set. - **4n= 12 Tetraploid** # Allopolyploidy - **A combination of genomes from different species.** The image shows a diagram of meiosis, where the chromosomes are duplicated and then separated. - The normal chromosomes are shown in the blue set. - The unreduced gametes are shown in the yellow set. - The hybrid with 7 chromosomes is shown in the pink and yellow set. - The viable fertile hybrid (allopolyploid) is shown in the blue set. - **Species A 2n=4 (Meiotic error, chromosome number not reduced from 2n to n)** - **Species B 2n = 6** - **Normal gamete n=3** - **2n=10** - **Normal gamete n=3** # Autopolyploidy vs Allopolyploidy | Autopolyploidy | Allopolyploidy | | :--------------------------------------------------------------------------- | :--------------------------------------------------------------------------- | | Refers to a type of polyploidy where the chromosome complement consists of more than two copies of homologous chromosomes. | Refers to a type of polyploidy where the chromosome complement consists of more than two copies of chromosomes derived from different species. | | Arises by the fusion of gametes of the same species. | Arises by the fusion of gametes of the different species. | | An autopolyploid cell contains homologous chromosome sets. | All chromosome sets of an allopolyploid cell are not homologous. | | Mainly caused by nondisjunction of chromosomes. | Caused by mating of different species. | | Does not undergo meiosis since it has arisen from one parent. | Can undergo meiosis. | | 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 # Allopolyploidy in Plant Breeding - **Raphanus 2n= 18:** An image shows the different parts of a radish plant. - **Parent (Brassica 2n=18)** - **Gametes (n=9)** - **Sterile F1 Hybrid (n+n=9+9 (2n)=(18))** - ** Raphanobrassicia (Fertile amphidiploid 2n+2n=18+18 (4n)=(36))** # The Formation of a Fertile Tetraploid Rabbage - The image shows a diagram of a radish plant (Raphanus) and a cabbage plant (Brassica), both of which are diploid (2n=18). - When the two plants are crossed, they produce a sterile hybrid (Raphanobrassica). - The hybrid is sterile because the chromosomes from the two parents are not homologous. - However, if the hybrid is treated with a chemical, such as colchicine, it can be induced to become a tetraploid (4n). - The tetraploid has two sets of chromosomes from each parent. - The chromosomes are now homologous, and the plant is fertile again. # 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), tetraploids. - **INTERSPECIFIC GENE TRANSFER:** In case of unavailability the desirable characters within the species, it is 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 meristemetic 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 The image shows a logo of the University of Nigde. # Aneupoidy vs Polyploidy | Aneupoidy | Polyploidy | | :-------------------------------------------------------------------------- | :-------------------------------------------------------------------------- | | Is the presence of an abnormal number of chromosomes. | Is the presence of more than two homologous chromosome sets. | | More common in humans. | Rare humans. | | Nullisomy, Monosomy, disomy, trisomy and tetrasomy are the different types. | Triploid, Tetraploid, Hexaploid, Octaploid, Dodecaploid, etc. are different types. | | Causes chromosomal disorders; some of them are lethal. | Triploid and tetraploid situations are lethal. | # TABLE 27.1 - Types of Polyploidy | Types of Polyploid | Definition/brief description | | :-------------------- | :---------------------------------------------------------------------------------- | | Polyploidy | A condition with more than two genomes | | 1. Autoployploidy | Multiplication of the same genome | | (a) Autotriploidy | Three copies of the same genome (3x) | | (b) Autotetraploidy | Four copies of the same genome (4x) | | (c) Autopentaploidy | Five copies of the same genome (5x) | | (d) Autohexaploidy | Six copies of the same genome (6x) | | 2. Allopolyploidy | A condition in which complete genomes of two or more species combine together. | | (a) Allotetraploidy | Two copies each of two distinct genomes (2x, + 2x₂) | | (b) Allohexaploidy | Two copies each of three distinct genomes (2x, + 2x2 + 2x) | | (c) Allooctaploidy | Two copies each of four distinct species (2x, + 2x + 2x + 2x) | # Table 5.2: Classification of aneuploids | Term | Chromosome number | | :---------- | :----------------- | | Monosomy | 2n-1 | | Nullisomy | 2n-2 | | Trisomy | 2n+2 | | Tetrasomy | 2n+2 | | Pentasomy | 2n+3 | # Inducing Polyploids - They occur spontaneously through the process of chromosome doubling. - Spontaneous chromosome doubling in ornamentals and forage grasses has led to increased vigour. - 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 may concurrently offer resistance to pests and pathogens. # Polyploidy can make the... - The image shows a diagram of a plant and its leaves, flowers and fruit. - **Polyploidy can make the...** - ...plant bigger. - ...flowers bigger. - ...fruits bigger. - ...leaves bigger. # Polyploidy Effect on Plant Size and Bolting Time - The image shows a graph of plant size vs. ploidy level. - **A:** Bolting time (days) vs Ploidy. - **B:** Rosette area (cm2) vs Ploidy. - **C:** Three pots showing three different ploidy levels (2n, 4n, 6n and 8n). The graph shows that as the ploidy level increases, the bolting time and rosette area also increase. This is because polyploidy can lead to increased cell size and overall plant size. The image of the pots also shows that the plants with higher ploidy levels are larger than those with lower ploidy levels.