Biology 9 Lesson 35: Hybrid advantage
1. Theoretical Summary
1.1. What is hybrid vigor?
– Concept: Hybrid dominance is the phenomenon where the F1 hybrid organism has higher vigor, faster growth, stronger development, better tolerance, and higher yielding traits than the average between the two parents or exceeds the superior to both parents.
– Hybrid advantage is created when crossing pure lines with different genotypes.
- AAbbDDeegg × aaBBddEEGG
- aabbddEEgg × AABBDDeeGG
– Hybrid superiority is also manifested when crossbreeding between things or strains. There can also be a hybrid dominance between two different species (Duck × Goose).
1.2. Causes of hybrid dominance
– When the pure lines carrying dominant genes for certain traits cross each other, in the F1 hybrid body, there will be full concentration of beneficial dominant genes from both parents, overwhelming the expression of harmful recessive genes. .
– Hybrid dominance is most evident in F1 and then gradually decreases over generations because of decreased heterozygosity (degenerative phenomenon).
– To maintain the hybrid advantage, it is necessary to use asexual propagation methods such as cuttings, extraction, grafting, tissue culture, etc.
– Hybrid dominance usually occurs when crossing quantitative traits (traits regulated by many genes).
1.3. Methods of creating hybrid advantage
a. Methods of creating hybrid dominance in plants
– There are two methods to create hybrid dominance in plants: cross-breeding and cross-breeding.
+ Cross-breeding: create 2 self-pollinating lines and then mate with each other.
- Example: F1 hybrid maize yields 20-30% higher than existing varieties.
+ Differential hybridization: combination of creating hybrid advantages and creating new varieties.
- For example: DT17 rice is created from a hybrid between DT10 (high yield) and OM80 (high quality) rice varieties with high yield and quality.
– Cross-breeding method is more often used to create hybrid advantage in cultivation because this method produces more high-yielding plant varieties than the best purebred varieties.
b. Methods of creating hybrid dominance in livestock
– Economic hybrid: It is for mating between 2 pairs of different parent animals and then using F1 hybrid as a product (not for breeding).
- For example: Mong Cai pig × Dai Bach pig → crossbred pig, new born weight weighs 0.8kg, gain weight quickly, lean percentage is high.
2. Illustrated exercise
Given the following gene lines: AABbDD, AaBBDD, AAbbDD, Aabbdd, aaBBdd, aabbdd. Randomly select 2 gene lines for crossbreeding. Hybrid dominance is most evident in the offspring of which hybrid? Why?
The F1 generation in the cross between two pure lines AAbbDD × aaBBdd showed the most obvious hybridization advantage, because F1 was 100% homogenous in terms of genotype and phenotype, and in the crossbred offspring carried all the dominant genes from both parents. exhibiting superiority to both parents.
3.1. Essay exercises
Question 1: What is hybrid vigor? What is the genetic basis of this phenomenon? Why not use F1 hybrids for breeding? What measures should be taken to maintain the future advantage?
Verse 2: In the selection of plant varieties, what methods are used to create hybrid advantages? Which method is most commonly used, and why?
Question 3: What is economic hybrid? In our country, economic hybridization is implemented in what form? For example.
3.2. Multiple choice exercises
Question 1: The hybrid advantage is most evident when performing the cross between:
A. Individuals of different species
B. Pure lines with different genotypes
C. Individuals born from a pair of parents
D. Male and female flowers on the same plant
Verse 2: To create a hybrid advantage, the first important step is
B. Economic hybrid
C. Hybrid analysis
D. Generating pure lines
Question 3: In creating hybrid dominance, forward and backward crosses between purebred lines for a purpose
A. detection of combinatorial variation.
B. determine the role of sex-linked genetics.
C. evaluate the role of cytoplasm on trait expression.
D. to find the most economical hybrid combination.
Question 4: Which of the following methods is not used to create a hybrid advantage?
A. Single line hybrid.
B. Other double line hybrid.
C. Close mating.
D. Economic hybrid.
After completing this lesson, you should:
- Present and analyze the causes of hybrid advantage.
- Explain why not use F1 hybrid showing dominant hybridization as breeding.