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Question
Define aneuploidy. How is it different from polyploidy?
Describe the individuals having following chromosomal abnormalities.
a. Trisomy of 21 st Chromosome
b. XXY
c. XO
Describe the individuals having following chromosomal abnormalities.
a. Trisomy of 21 st Chromosome
b. XXY
c. XO
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Solution
Definition of aneuploidy:
Aneuploidy is the chromosomal variation that occurs due to a loss or a gain of chromosome resulting in the deviation from the normal chromosome count in a particular species. For example, (2n+1) condition in Down’s syndrome.
Definition of polyploidy:
Polyploidy is the condition when more than two complete sets of the chromosomes are present in an organism. For example, 3n, 4n etc.
Difference between aneuploidy and polyploidy:
Criteria
Aneuploidy
Polyploidy
Condition
It is caused because of gain and loss of chromosomes
It is caused when there is an increase in the whole set of chromosomes
Types
Nullisomy (2n-2), Monosomy (2n-1), Trisomy (2n+1), Tetrasomy (2n+2)
Triploid (3n),
Tetraploid (4n), Pentaploid (5n)
Example
Down’s syndrome in humans
Some hepatocytes in humans
Trisomy of 21st chromosome:
Down syndrome is caused by trisomy of the 21st chromosome. Here, the individual has three copies of chromosome 21, instead of the usual two copies. This occurs due to the non-disjunction in meiosis during the formation of a sperm cell or the egg cell.
The risk of Down’s syndrome increases with women’s age.
Symptoms of Down’s syndrome:
- Round face
- Broad forehead
- Short statured with small round head
- Furrowed tongue and partially opened mouth
- Broad palm with a characteristic palm crease
- Retareded physical, psychomotor, and mental development
- Low intelligence
XXY:
Klinefelter’s syndrome is caused by XXY genotype. The individual has 47 (2n+1) chromosomes. It is due to trisomy. The individual has 47 chromosomes (44+XXY) instead of 46 in this condition.
This condition arises due to the following reasons:
- Fusion of normal sperm with egg containing an extra X chromosome.
- Fusion of normal egg with abnormal sperm carrying one X chromosome in addition to the Y chromosome.
Symptoms of Klinefelter’s syndrome:
Symptoms of Klinefelter’s syndrome include the following:
- Sterile male having small testes.
- The individuals are with some feminine characteristics such as sparse body hair, high pitched voice and enlarged breasts (gynaecomastia).
- They also show mental retardation.
XO:
Turner's syndrome is caused due to XO genotype. The individual has 45 (2n-1) chromosomes. It is due to monosomy of the X chromosome. It occurs due to the following reasons:
- Fusion of normal egg with abnormal sperm lacking the allosome.
- Fusion of normal sperm carrying X chromosome with abnormal egg lacking the allosome.
Symptoms of Turner’s syndrome:
Symptoms of Turner’s syndrome:
- Sterility
- Short statured
- Male characteristics like heavy neck and narrow lips
- Underdeveloped breasts
- Abnormal intelligence
Aneuploidy is the chromosomal variation that occurs due to a loss or a gain of chromosome resulting in the deviation from the normal chromosome count in a particular species. For example, (2n+1) condition in Down’s syndrome.
Definition of polyploidy:
Polyploidy is the condition when more than two complete sets of the chromosomes are present in an organism. For example, 3n, 4n etc.
Difference between aneuploidy and polyploidy:
| Criteria | Aneuploidy | Polyploidy |
| Condition | It is caused because of gain and loss of chromosomes | It is caused when there is an increase in the whole set of chromosomes |
| Types | Nullisomy (2n-2), Monosomy (2n-1), Trisomy (2n+1), Tetrasomy (2n+2) | Triploid (3n), Tetraploid (4n), Pentaploid (5n) |
| Example | Down’s syndrome in humans | Some hepatocytes in humans |
Trisomy of 21st chromosome:
Down syndrome is caused by trisomy of the 21st chromosome. Here, the individual has three copies of chromosome 21, instead of the usual two copies. This occurs due to the non-disjunction in meiosis during the formation of a sperm cell or the egg cell.
The risk of Down’s syndrome increases with women’s age.
Symptoms of Down’s syndrome:
- Round face
- Broad forehead
- Short statured with small round head
- Furrowed tongue and partially opened mouth
- Broad palm with a characteristic palm crease
- Retareded physical, psychomotor, and mental development
- Low intelligence
XXY:
Klinefelter’s syndrome is caused by XXY genotype. The individual has 47 (2n+1) chromosomes. It is due to trisomy. The individual has 47 chromosomes (44+XXY) instead of 46 in this condition.
This condition arises due to the following reasons:
- Fusion of normal sperm with egg containing an extra X chromosome.
- Fusion of normal egg with abnormal sperm carrying one X chromosome in addition to the Y chromosome.
Symptoms of Klinefelter’s syndrome:
Symptoms of Klinefelter’s syndrome include the following:
- Sterile male having small testes.
- The individuals are with some feminine characteristics such as sparse body hair, high pitched voice and enlarged breasts (gynaecomastia).
- They also show mental retardation.
XO:
Turner's syndrome is caused due to XO genotype. The individual has 45 (2n-1) chromosomes. It is due to monosomy of the X chromosome. It occurs due to the following reasons:
- Fusion of normal egg with abnormal sperm lacking the allosome.
- Fusion of normal sperm carrying X chromosome with abnormal egg lacking the allosome.
Symptoms of Turner’s syndrome:
Symptoms of Turner’s syndrome:
- Sterility
- Short statured
- Male characteristics like heavy neck and narrow lips
- Underdeveloped breasts
- Abnormal intelligence
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