Question

☛ Define aneuploidy. How is it different form polploidy ? Describe the individuals having the following chromosomal abnormalities?
(i) Trisomy of 21st chromosome.

ii) XXX

iii) XO


And what are the different types of aneuploidy , give its examples with justification.


¤¤ CLASS XIIth. { GENETICS }​

Answer 1

Answer:

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Explanation:

Aneuploidy is the condition used to describe a chromosomal alteration that is caused by an addition or deletion of one or a few chromosomes; It results in genetic disorders.

It differs from polyploidy which is the addition of one or more complete sets of chromosome in the genome.  Individuals having following chromosomal abnormalities are defined as:

(i) Trisomy of 21st chromosome It is also known as Down’s syndrome. In this, a person is born with three chromosomes at 21st position rather than normal pair.

(ii) XXX It is also known as triple X-syndrome or Klinefelter’s syndrome. This condition can occur only in females where they have three X-chromosomes instead of two.

(iii) XO It is also known as Turner’s syndrome. It always

affects the females in which one of the two chromosomes are defective or completely absent. The individuals with this syndrome are born with 45 chromosomes in each cell rather than 46.

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Two common types of aneuploidy have their own special names:

Monosomy is when an organism has only one copy of a chromosome that should be present in two copies (2n-1)(2n−1)left parenthesis, 2, n, minus, 1, right parenthesis.

Trisomy is when an organism has a third copy of a chromosome that should be present in two copies (2n+1)(2n+1)left parenthesis, 2, n, plus, 1, right parenthesis.

Euploid cell: a human cell with the normal chromsome number, 2n = 46. The chromosomes are arranged in 23 pairs.

Aneuploid cell, example 1: monosomy. A human cell with a missing chromosome, in this case, chromosome 3. All the other chromosomes are still arranged in pairs of two, but there is just one copy of chromosome 3. The chromosome number of this cell is 2n-1 = 45.

Aneuploid cell, example 2: trisomy. A human cell with an extra chromosome, in this case, an extra copy of chromosome 3. All the other chromosomes are still arranged in pairs of two, but there are three copies of chromosome . The chromosome number of this cell is 2n+1 = 47.

Aneuploidy also includes cases where a cell has larger numbers of extra or missing chromosomes, as in (2n - 2), (2n + 3)(2n−2),(2n+3)left parenthesis, 2, n, minus, 2, right parenthesis, comma, left parenthesis, 2, n, plus, 3, right parenthesis, etc. However, if there is an entire extra or missing chromosome set (e.g., 3n3n3, n), this is not formally considered to be aneuploidy, even though it may still be bad for the cell or organism. Organisms with more than two complete sets of chromosomes are said to be polyploid.

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Answer 2

Aneuploidy:A condition in which a person has one or a few chromosomes above or below the normal chromosome number. For example, three copies of chromosome21, which is characteristic of Down syndrome, is a form of aneuploidy.

Aneuploidy vs Polyploidy:-

Aneuploidy is a chromosomal mutation in which there is one or more extra chromosomes, or one or more fewer chromosomes. In humans, the genetic disorders Down syndrome and Turner's syndrome are examples of aneuploidy. Individuals with Down syndrome have three copies of chromosome 21, so their genomes contain 47 chromosomes rather than the usual 46. Individuals with Turner syndrome have only one sex chromosome, which is the X-chromosome, so their genomes contain 45 chromosomes.

Aneuploidy is a chromosomal mutation in which there is one or more extra chromosomes, or one or more fewer chromosomes. In humans, the genetic disorders Down syndrome and Turner's syndrome are examples of aneuploidy. Individuals with Down syndrome have three copies of chromosome 21, so their genomes contain 47 chromosomes rather than the usual 46. Individuals with Turner syndrome have only one sex chromosome, which is the X-chromosome, so their genomes contain 45 chromosomes.Polyploidy is a chromosomal mutation in which a cell has entire extra sets of chromosomes. Instead of being diploid, in which the cell contains two sets of chromosomes, it may be triploid (three sets of chromosomes), or tetraploid (four sets of chromosomes). Polyploidy is common in plants, and plant growers may exploit this fact to produce plants with flowers having double petals. Polyploidy is generally lethal in animals.

(i). TRISOMY OF THE 21st CHROMOSOME : Result in Down's syndrome. Individual has a prominent forehead, lower hip with a large protruding tongue, skinfolds and corners of the eyes, malformed heart and under developed gonads and genitalia.  

(ii)XXX: Results in Klinefelter syndrome. Such an individual is a male in appearance with femalecharacteristics. The person has long limbs, enlarged breasts, sparsely body hair and underdeveloped tests. Such individual is often sterile and mentally defective.  

(iii)XO  : Results in Turner's syndrome. Such individuals are underdeveloped females with a single X - chromosome. The females have rudimentary ovaries, shield shaped thorax, short stature and abnormal intelligence. Menstruation and ovulation do not happen in these females. 

Forms of Aneuploidy:

Forms of Aneuploidy:Monosomy:

Forms of Aneuploidy:Monosomy:Monosomy is the phenomenon where an individual lacks one or a few non-homologous chromosome(s) of a diploid complement.

Nullisomy:

Nullisomy:The plants in which a chromosome pair is missing, are called nullisomics. The chromo­some formula would be (2n – 2) and not (2n – 1 – 1), which would mean a double monosomic. The number of possible nullisomics in an orga­nism will be equal to the haploid chromosome number.

Trisomy:

Trisomies are those organisms, which have an extra chromosome (2n -t- 1). The number of possible trisomies in an organism is equal to the haploid chromosome number.

  Tetrasomy:

 Tetrasomy:Tetrasomics have a particular chromosome represented in four doses (2n+2). The types of possible tetrasomics is equal to the haploid chro­mosome number of an organism. All 21 possible tetrasomics are available in wheat.

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