What is crossbreeding?
Crossing is one of the methods of plant and animal breeding, during which two different genotypes are joined by natural or artificial means through fertilization. There are many types of crossbreeding - analyzing, monohybrid, dihybrid, intraspecific, diallel, stepped, etc., however, we will analyze only the most popular ones. So, let's see what crossing is and what it is for.
Crossing with the help of numerous experiments helps to identify new varieties of plants - more resistant to those or other harmful influences, as well as to obtain new breeds of animals. The main tasks of crossing:
- combining traits of the original organisms in the final one;
- enrichment of the hereditary basis;
- increased resilience and survival.
Genetics - the science of interbreeding
Genetics is the science of the laws of heredity and variability of organisms, including crossing. Basic terms of genetics:
- Dominant trait - the predominant trait, may occur in the homo-and heterozygous state in the offspring;
- Recessive trait - a suppressed trait, always appears in the homozygous state;
- Homozygote - zygote, which has the same alleles of the same gene (AA, aa);
- Heterozygote - zygote, which has different alleles of the same gene (Aa);
- Allelic genes - genes located in the same places of homologous chromosomes;
- Homologous chromosomes - a pair of chromosomes that carry the same hereditary information.
This type of crossing is used to determine the genotype of the organism. In order to establish this moment, an organism is taken, the genotype of which is unknown, and it is crossed with an organism that is a recessive homozygous for the trait under study. What does it mean? Let's take an example.
We need to understand the genotype of yellow peas, it can have two variants of the genotype - a heterozygote (denoted by AA) and a dominant homozygote (denoted by AA). To cross we take green peas - a plant with a recessive homozygote (aa). In the event that, after crossing, both yellow and green peas are obtained, the genotype of the individual is heterozygous, otherwise it is dominantly homozygous.
Monohybrid crossing is the crossing of organisms that differ by only one sign.In the first generation, all hybrids obtained by monohybrid crossing are uniform — heterozygous. So, if you cross a night beauty plant (Mirabilis jalapa) with red flowers with a night beauty with white flowers, all plants of the first generation will have pink flowers.
Hybrid crossing is the crossing of organisms that differ in two ways, for example, the color of flowers and the shape of the seeds. The most famous experiments on hybrid crossing of the Austrian biologist Mendel. He took two types of pea seeds - one - yellow and smooth, the second - green and wrinkled. All hybrids of the first generation were yellow and smooth, as a result, it became clear that the yellow color and smoothness are dominant. In the second generation, green wrinkled peas appeared again.