Difference Between Trisomy and Triploidy

Main Difference – Trisomy vs Triploidy

Trisomy and triploidy are two types chromosomal abnormalities. Trisomy is a type of aneuploidy whereas triploidy is a type of euploidy. The main difference between trisomy and triploidy is that trisomy is the presence of three homologous chromosomes whereas triploidy is the presence of three sets of chromosomes in the nucleus. Trisomy 21 or Down syndrome is an example of trisomy in humans. Triploidy mainly occurs in plants as a result of complete non-disjunction of a chromosome set during the formation of gametes.

Key Areas Covered

1. What is Trisomy
– Definition, Facts, Examples
2. What is Triploidy
– Definition, Facts, Examples
3. What are the Similarities Between Trisomy and Triploidy
– Outline of Common Features
4. What is the Difference Between Trisomy and Triploidy
– Comparison of Key Differences

Key Terms: Aneuploidy, Chromosomal Non-disjunction, Chromosome Sets, Chromosomes, Down Syndrome, Euploidy, Triploidy, Trisomy

What is Trisomy

Trisomy refers to the condition of having an additional copy of a chromosome in the genome. This means a particular chromosome of the nucleus occurs in triplets in trisomy. Trisomy is a type of aneuploidy. Typically, trisomy arises as a result of non-disjunction of homologous chromosomes during the production of gametes by meiosis. The gametes formed in trisomy consist of 24 chromosomes (instead of 23). Generally, trisomy can occur in any chromosome of the genome. But, most of them are lethal except in chromosomes 13, 18, 21, X and Y. Maternal age is a risk factor of non-disjunction. Trisomy 21 or Down syndrome is the commonest, viable trisomy. The karyotype of the Down syndrome is shown in figure 1.

Figure 1: Down Syndrome

Trisomy 13 or Patau syndrome and trisomy 18 or Edward syndrome are rare types of trisomies that cause severe congenital malformations. They also cause mental retardation, resulting in death within a few months of birth. Trisomy leads to the formation of imbalanced amounts of gene products.

What is Triploidy

Triploidy refers to the presence of an extrachromosomal set in diploid organisms. This means the number of chromosome sets in the nucleus is three in triploidy. Triploidy is a type of euploidy. Triploidy is a very rare chromosomal disorder in humans. In triploid humans, 69 chromosomes are present in the nucleus. Generally, the human genome (2n) consists of 46 chromosomes. Maternal triploidy occurs due to the fertilization of a diploid ovum by a haploid sperm. Other than that, triploidy occurs due to the complete non-disjunction of chromosomes during meiosis. Most conceptions with triploidy in humans do not survive till birth. The triploid condition of a nucleus is shown in figure 2.

Difference Between Trisomy and Triploidy

Figure 2: Triploidy

Triploidy is more common in plants. In plants, triploidy mainly arises due to interspecies crosses where the gametes are fused from distinct species distinct species. Triploidy may lead to sympatric speciation in plants.

Similarities Between Trisomy and Triploidy

Trisomy and triploidy are two types of chromosomal abnormalities.
Both trisomy and triploidy carry the corresponding entity in the nucleus in ‘3’ numbers or as a triplet.
Both trisomy and triploidy may be lethal in humans.
Both trisomy and triploidy lead to birth defects in humans.

Definition

Trisomy: Trisomy refers to the condition of having an additional copy of a chromosome in the genome.

Triploidy: Triploidy refers to the presence of an extrachromosomal set in diploid organisms.

Type of Chromosomal Abnormality

Trisomy: Trisomy is a type of aneuploidy.

Triploidy: Triploidy is a type of euploidy.

Type of Entity

Trisomy: Trisomy is the presence of three homologous chromosomes in a particular chromosome.

Triploidy: Triploidy is the presence of three chromosome sets in a particular nucleus.

Occurrence

Trisomy: Trisomy occurs in both animals and plants.

Triploidy: Triploidy mainly occurs in plants.

Role

Trisomy: Trisomy leads to the imbalance in the number of gene products.

Triploidy: Triploidy may lead to the formation of new species.

Effect

Trisomy: Trisomy leads to severe abnormalities in humans.

Triploidy: Triploidy may lead to more severe conditions in humans.

Examples

Trisomy: Down syndrome of humans is an example of trisomy.

Triploidy: The 3n nuclei are examples of triploidy.

Conclusion

Trisomy and triploidy are two terms that describe abnormal nuclei with a particular entity as a triplet. In trisomy, three homologous chromosomes are present in the nucleus while in triploidy, three chromosome sets are present in the genome. Therefore, the main difference between trisomy and triploidy is the type of entity that is abnormal.

Reference:

1. “Triploidy and chromosomes.” American Journal of Obstetrics and Gynecology, Mosby, 18 Oct. 2013, Available here.
2. “Trisomy disorders.” Better Health Channel, Department of Health & Human Services, 30 Aug. 2013, Available here.

Image Courtesy:

1. “21 trisomy – Down syndrome” By U.S. Department of Energy Human Genome Program. – (Public Domain) via Commons Wikimedia
2. “Haploid, diploid ,triploid and tetraploid” By Haploid_vs_diploid.svg: Ehambergderivative work: Ehamberg (talk) – Haploid_vs_diploid.svg (CC BY-SA 3.0) via Commons Wikimedia