Shellfish polyploid breeding techniques (2)

The polyploid type and genetic basis Polyploidy is quite common in higher plants. For example, about 1,000 or more species of flowering plants are polyploid, and they are more common in cultivated plants. Plants up to 75%. However, there are far fewer polyploids in the animal kingdom and fewer vertebrates [3]. Since Stanley induced the success of oyster triploids, polyploid breeding has become the most active research area in shellfish genetics and breeding. Many scholars at home and abroad have carried out a large amount of research on shellfish polyploid breeding and have made gratifying progress [4].
The types of polyploids are divided into natural polyploids and artificial polyploids based on their production methods; Homologous polyploids and allopolyploids are classified according to their chromosomal origin ( (Heterologous polyploid); According to chromosome number, it is divided into triploid, tetraploid, hexaploid, octoploid, and so on [3,5].
All organisms that contain a set of chromosomes in a somatic cell are called haploids and are represented by n. Two sets of chromosomes are called diploids, and 2n are used. Most of the organisms found in nature are diploids. Polyploids will form as a result of natural or human factors that increase the number of genomes in somatic cells. Shellfish sperm have completed two meiotic divisions prior to discharge to form haploid sperm, and eggs, especially bivalves, usually stop in the early or mid-stage of the first meiotic discharge. After meiosis is completed after fertilization or after activation, two polar bodies are released, and the male and female pronuclei are fused or combined to enter the first mitosis, ie cleavage. This delayed meiosis process provides favorable timing and conditions for the polyploid breeding of shellfish. To date, polyploidy studies have been performed in more than 30 species of shellfish using various methods [5,6].