Asexual reproduction includes fission reproduction, budding reproduction, spore reproduction and vegetative reproduction.

Vegetative reproduction refers to the reproductive mode of producing new individuals from vegetative organs (roots, leaves and stems) of plants, which is called vegetative reproduction. For example, the tubers of potatoes, the roots of thistles, the creeping branches of strawberries and the leaves of begonia can all germinate, and these buds can form new individuals.

Nutritional reproduction can make offspring keep their parents' traits, so people often use artificial methods such as rooting, cutting, grafting, layering and high pressure to propagate flowering fruit trees.

The vegetative propagation in the natural state is called natural vegetative propagation. Such as strawberry creeping branches, begonia leaves and potato tubers; Artificial assisted vegetative propagation is called artificial vegetative propagation. Such as cutting and grafting

Cutting: Cut branches into small pieces, insert them into the soil, and take root and sprout into new plants.

Grafting: Grafting the branches (or buds) of one plant to the branches of another plant, so that the cambium of the two plants is aligned, so that they can heal each other and grow into a plant.

Scion: a grafted bud or branch.

Rootstock: a grafted plant

Survival principle: use the regenerative ability of cambium.

The key to survival: pay attention to make the cambium of scion and rootstock close together. In this way, the cells split from the cambium combine the scion with the rootstock.

The conditions for asexual propagation of plants such as cuttings are as follows: 1. Stem segments (keep two segments), the upper incision is horizontal and the lower incision is inclined, except for environmental conditions such as light, moisture, temperature and humidity; 2. Blade: the last section is removed, and the next section is completely removed.

tissue culture

Plant cells are omnipotent. According to this theory, plant propagation can be completed by using plant tissue culture technology. The general process of plant tissue culture is as follows: under aseptic conditions, plant organs, tissues and cells are cut off and cultured in an appropriate artificial medium, and these organs or tissues will undergo cell division and form new tissues. However, this tissue has not undergone cell differentiation. Under the action of proper light, temperature, some nutrients and plant hormones, these cells begin to differentiate, produce tissues and organs, and then develop into complete plants.

Plant tissue culture is not only less material, short culture period, high reproduction rate and virus-free, but also convenient for automatic management. This technology has been widely used in the rapid propagation of fruit trees and flowers and the cultivation of virus-free plants. For example, the shoot tips of orchids and chrysanthemums can produce 400,000 orchid seedlings a year. For another example, plants that reproduce asexually for a long time often accumulate a large number of viruses in their bodies, thus affecting the yield and ornamental value of plants. It has been found that only the shoot tip and root tip are virus-free. Therefore, people have obtained virus-free strains of many plants, such as potatoes, strawberries, chrysanthemums, etc., by using stem tips for tissue culture, and achieved considerable economic benefits.

clone

A group of cells or individuals with the same genetic structure formed by asexual reproduction of precursors. For gene cloning, it refers to multiple copies of a gene after repeated amplification.

Firstly, the nucleus of a donor cell containing genetic material is transplanted into an egg cell without nucleus, and then the two cells are fused into one by micro-current stimulation, and then the new cell is promoted to divide and reproduce and develop into an embryo. When the embryo develops to a certain extent, it is implanted into the uterus of an animal to make the animal pregnant, so that an animal with the same gene as the cell donor can be born. In this process, if the donor cells are genetically modified, the genes of the offspring of asexual animals will also change in the same way.

Cloning technology does not require male and female mating, and does not require the combination of sperm and eggs. It only needs to extract single cells from animals, cultivate them into embryos by artificial methods, and then implant the embryos into female animals to breed new individuals. This cloned animal cultured with single cells has exactly the same characteristics as the single-cell donor and is a "replica" of the single-cell donor. Scientists in Britain and Oregon in the United States have successively cultivated "cloned sheep" and "cloned monkeys"

. The success of cloning technology is called "historic event and scientific innovation". Some people even think that cloning technology can be compared with the advent of the atomic bomb that year.

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Other instructions

1. Most single-celled organisms divide and reproduce, and protozoa can also reproduce sexually.

2. The "bud" in "bud grafting propagation" refers to the bud growing on the mother, not the structure of the real bud on higher plants. For example, potatoes are propagated by buds or tubers, which are vegetative rather than budding. In essence, the "bud" is the same as the mother, but the bud is smaller.

3. Spores in asexual reproduction "spores" in asexual reproduction are asexual spores with the same number of chromosomes or DNA as somatic cells. Therefore, asexual spores can only be produced by mitosis or amitosis, but not by meiosis.

4. Vegetative reproduction is reproduction by using vegetative organs of plants. Only higher plants can differentiate roots and leaves. Therefore, it is an asexual reproduction mode of higher plants, and it is impossible for lower plant cells to carry out vegetative reproduction.

Dolly, a sheep bred by British scientists with cloning technology from 65438 to 0997, is one of them. China has also made great achievements in the research of cloning technology. For example, shortly after Dolly was born, the success rate of cloning goats in China was 10~20 times that of cloning sheep Dolly.