Biology 9 Lesson 34: Degeneration due to self-pollination and close mating
1. Theoretical Summary
1.1. Degenerative phenomenon
a. Degeneration due to self-pollination in cross-pollination plants
Degeneration due to self-pollination in cross-pollination plants is the phenomenon where individuals of the next generation gradually show signs of slow growth, reduced plant height and yield, and many plants die. , exhibiting harmful characteristics.
For example: sapodilla, pomelo, lychee degenerate small fruit, few fruits, not sweet.
b. Degenerative phenomenon due to close mating in animals
Close mating (inbreeding) is the mating between offspring of one parent or between parents and their offspring.
Close mating causes degenerative phenomena in the progeny: Weak growth and development, reduced fertility, teratogenicity, birth defects, stillbirth.
1.2. Causes of degeneration
Self-pollination in plants or close interbreeding in animals causes degeneration by creating homozygous recessive gene pairs that are harmful to the body’s expression.
1.3. The role of self-pollination and inbreeding in breeding
In plant and animal breeding, self-pollination and inbreeding methods are used to consolidate and maintain some desired traits, create pure lines, and facilitate the genotyping of plants. each line, detect bad genes to eliminate from the population, prepare to cross the line to create hybrid advantage.
2. Illustrated exercise
In breeding, what are these two methods used for?
In breeding, people use these two methods to consolidate and keep the stability of some desired traits, create pure lines with homozygous gene pairs that are favorable for genotyping, and detect bad genes. eliminated from the body.
3.1. Essay exercises
Question 1: Why can forced self-pollination in cross-pollination and close interbreeding in animals over many generations cause degeneration? For example.
Verse 2: With 2 alleles A and a, start with all individuals with genotype Aa. Self-pollination takes place continuously over 3 generations. Determine the proportion of genotypes in the third generation of self-pollination?
Question 3: With 2 alleles A and a, start with all individuals with genotype Aa. Self-pollination takes place continuously over 3 generations. Determine the proportion of genotypes in the nth generation of self-pollination?
Question 4: A population of self-pollinated plants has a lotus-type ratio in the initial generation: 0.45AA: 0.30Aa: 0.25aa. Indicates that individuals with genotype aa are not fertile. Theoretically, what proportion of genotypes are obtained in the next generation?
3.2. Multiple choice exercises
Question 1: The causes of seed degeneration in crossbreeding plants are:
A. Because crossbreeding occurs randomly between plants
B. Due to different hybrids
C. Due to forced self-pollination
D. Due to crosses between pure lines with different genotypes
Verse 2: Inbreeding is:
A. Mating between individuals with different parents
B. Crossing between plants with the same genotype
C. Interbreeding between individuals with different genotypes
D. Mating between individuals with the same parents or mating between children and their parents
Question 3: People use inbreeding and self-pollination in breeding mainly to
A. Consolidation of precious characteristics, creating pure lines.
B. create new varieties.
C. test and evaluate the genotype of each pure line.
D. create hybrid advantage.
Question 4: Which of the following is not a result of close mating?
A. degenerative phenomenon.
B. homozygous increase, heterozygous decrease.
C. the rate of homozygotes decreases, heterozygotes increase.
D. generate pure lineage.
After completing this lesson you should:
- Understand and present the degenerative causes of forced self-pollination in cross-breeding plants and close interbreeding in animals, the roles of the two above cases in breeding.
- Describe the method of creating pure lines in cross-pollination plants.