What are the four main technical steps of breeding?

Biological breeding methods and their differences.

Best answer

1. Cross breeding:

Principle (1): Gene recombination (separating excellent traits or bringing all kinds of excellent traits together through gene separation, free combination or linkage exchange).

(2) Method: Self-pollination and continuous seed selection.

(3) For example:

It is known that tall stalk (D) is dominant for short stalk (D), rust resistance (R) is dominant for susceptible rust (R), and two pairs of traits are inherited independently. At present, there are two pure varieties: rust-resistant and susceptible to short stalks. It is necessary to cultivate new varieties with excellent characters through cross breeding.

How to operate: (see the right)

(1) F 1 is obtained by crossing pure wheat with high resistance to stem rust and dwarf rust;

② F 1 selfed to obtain F2;

(3) selecte F2 medium-short rust-resistant wheat and selfing to obtain F3;

(4) Leave the dwarf disease-resistant individuals without trait segregation in F3, and repeat steps (3) and (4) for trait segregation in F3.

(4) Characteristics: The breeding cycle is long, and it is necessary to constantly select the superior and eliminate the inferior in order to breed the required types.

(5) Description:

(1) This method is often used for:

A. between individuals of different varieties of the same species, as in the above example;

B between individuals of different species with close genetic relationship (in order to make offspring fertile, chromosome doubling is needed to obtain individuals who are allopolyploids), such as the cultivation of octoploid triticale and the hybridization of radish and cabbage.

(2) If an organism reproduces its offspring through sexual reproduction, it must choose a purebred with excellent traits to prevent the offspring from character separation; If an organism produces offspring through asexual reproduction, it only needs to obtain excellent traits, and purebred and hybrid do not affect the expression of offspring traits.

2. Mutation breeding

(1) principle: gene mutation

(2) Methods: Physical factors (such as X-ray, γ-ray, ultraviolet ray, laser, etc. ) or chemical factors (such as nitrous acid, diethyl sulfate, etc. ) is used to treat organisms, making them make mistakes in DNA replication during cell division, thus causing gene mutation.

(3) Example: Space breeding, obtaining high-yield penicillin strains.

(4) Characteristics: improve the mutation rate, create the mutation types needed by human beings, and select and cultivate excellent biological varieties from them. However, this breeding method is blind because of non-directional mutation.

(5) Description: This method is often used in microbial breeding and crop mutation breeding.

3. Haploid breeding

(1) principle: chromosome variation

(2) Methods: Haploid plants were obtained by anther culture in vitro, and then the number of chromosomes was artificially induced to double.