Variation in chromosome structure and number - Variation in the number of chromosomes within a set: aneuploidy

4 important questions on Variation in chromosome structure and number - Variation in the number of chromosomes within a set: aneuploidy

Why does aneuploidy commonly cause an abnormal phenotype?

The level of gene expression is influenced by the number of genes per cell. When a person has 3 copies of a chromosome instead of 2, 150% of all the gene products normally made, are made. This results in an imbalance among many genes.

5%-10% of all fertilized human eggs result in an embryo with an abnormality in chromosome number. What happens in most of those cases?

A spontaneous abortion occurs. Only trisomies in chromosome 13, 18 and 21 are not immediately lethal.

Why do individuals with trisomy X often survive?

Because of X-chromosome inactivation (all additional X chromosomes are converted to Barr bodies).
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To what syndroms does trisomy and monosomy X lead?

XXY - Kleinfelter Syndrome
XYY - Jacobs Syndrome
XXX - Triple X Syndrome
X0 - Turner Symdrome

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