Biology 9 Lesson 23: Chromosome number mutations
1. Theoretical Summary
1.1. The concept of chromosome number mutation
Chromosome number mutations are quantitative changes that occur in one or more pairs of chromosomes or all sets of chromosomes.
1.2. Types of mutations in the number of chromosomes
There are two types of chromosome number mutations: aneuploidy and polyploidy.
a. Heterozygous body
– Definition: Heterozygous organism is an organism in which one or several pairs of chromosomes have an altered number in a somatic cell.
Some common aneuploidy forms:
- 2n-1 (monosome): Loss of 1 chromosome in a pair of chromosomes
- 2n+1 (trisomy): 1 extra chromosome in a pair of chromosomes
- 2n-2 (zero form): Loss of both chromosomes in a pair of chromosomes
- 2n+2 (quad): 2 extra chromosomes in a pair of chromosomes
+ Consequences of aneuploidy often cause changes in shape, size, color or cause disease syndromes in humans (Dao, Torno…).
– Mechanism of aneuploidy
+ In meiosis, there is a pair of homologous chromosomes that do not segregate equally about gametes, resulting in a gamete with n+1 chromosome set and 1 gamete with n-1 chromosome set. When these gametes fertilize normal gametes, haploid bodies are produced.
– The meaning of heterozygosity:
- For breeding: It is possible to use the null body to get the desired chromosomes into the hybrid organism.
- For genetics: aneuploidies can be used to locate genes on chromosomes.
- For evolution: Provides materials for evolution.
2. Illustrated exercise
Rice has a diploid set of 2n=24 chromosomes. What is the maximum number of chromosomes in a rice cell when an aneuploidy mutation occurs? Explain why?
The maximum number of chromosomes in a rice cell when a heterozygous mutation occurs is 48. Because each chromosome can only increase by 2 chromosomes, that is twice the number of chromosomes in the cell.
3.1. Essay exercises
Question 1: What mechanism leads to the formation of bodies (2n+1) and (2n-1)?
Verse 2: What are the consequences of aneuploidy?
Question 3: In what types of changes in the number of a pair of chromosomes are usually found?
a) Triple infection;
b) Single infection;
c) Non-infectious form;
d) Both a, b and c.
Question 4: In a plant, the diploid set is 24 chromosomes.
Determine the number of chromosomes in each cell of some individuals of the following species, given that:
1. The process of mitosis 3 times from 1 cell of individual B was obtained from the intracellular environment material created with 175 single chromosomes.
2. The process of mitosis 3 times from 1 cell of individual c produces the number of cells in the final generation of cells with 184 chromosomes in the unduplicated state.
3.2. Multiple choice exercises
Question 1: Heterozygous organisms are organisms in which in vegetative cells:
A. Only one pair of chromosomes is altered in number
B. Only one or several chromosomes are structurally altered
C. All pairs of chromosomes are changed in number
D. Having one or several pairs of chromosomes altered in number
Verse 2: Toadstool has a set of 2n=24 chromosomes. Therefore, the body (2n-2) of the toadstool has the number of chromosomes in the cell:
Question 3: A pair of homologous chromosomes is designated Aa. If this pair of chromosomes does not segregate at the end of meiosis I, what types of gametes will be produced?
A. AA, Aa, A, a.
B. Aa, O.
C. AA, O.
D. Aa, a.
Question 4: In a plant species, the diploid set of chromosomes is 24. A single cell of individual A mitosis three times in a row, resulting in the number of cells in the final cell generation having a total of 192 chromosomes in the unduplicated state. What is the number of chromosomes in each cell?
After completing this lesson, you should:
- Describe what is a mutation in the number of chromosomes.
- Analyze the mechanism of aneuploidy.