Individuals with trisomy 21 are more likely to survive to...

Individuals with trisomy 21 are more likely to survive to adulthood than individuals with trisomy
18. Based on what you know about aneuploidies from this module, what can you hypothesize about chromosomes 21 and $18 ?$

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Key Concepts

Gene Dosage Imbalance

Gene dosage refers to the number of copies of a particular gene present in a cell. A balance in gene dosage is critical for normal development. In trisomy conditions, the extra copy leads to overexpression of genes. The discrepancy in viability between trisomy 21 and trisomy 18 likely stems from differences in susceptibility to dosage imbalance, where the extra genetic material on chromosome 18 disrupts development more severely than that on chromosome 21.

Aneuploidy

Aneuploidy refers to the condition where a cell has an abnormal number of chromosomes. It is significant because the presence of extra or fewer chromosomes can disrupt the balance of gene expression and lead to developmental challenges or diseases. Understanding aneuploidy is essential for explaining why specific chromosomal imbalances have varying effects on survival and phenotype.

Chromosomal Gene Content and Size

Chromosomes differ in terms of the number of genes they contain and the importance of those genes to development. Chromosome 21 has relatively fewer genes compared to some other chromosomes, meaning that an extra copy (as seen in trisomy 21) causes a milder imbalance compared to an extra copy of a larger chromosome like chromosome 18, which carries more crucial genes necessary for early development.

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