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How does having 47 chromosomes lead to physical defects?

Best Answers

…What's wrong with having 'Aaa 'genotype instead of 'Aa' since you're sure only the dominant allele is expressed ? Because that's not how dominance works. Let's look at one of tha canonical examples of dominance: pea flowers. The relevant gene here produces purple pigment. read more

A translocation of part or all of 21 to another chromosome does not add genetic material to the individual. It just moves material around so the individual is normal. But an offspring may inherit the extra material, one #21 from each parent and also the “enhanced” chromosome with translocation. read more

Other factors that can increase the risk of chromosome abnormalities are: Maternal Age: Women are born with all the eggs they will ever have. Some researchers believe that errors can crop up in the eggs' genetic material as they age. Older women are at higher risk of giving birth to babies with chromosome abnormalities than younger women. read more

"Tri-" is Greek for "three"; people with trisomy have three copies of a particular chromosome in cells instead of the normal two copies. Down syndrome is an example of a condition caused by trisomy. People with Down syndrome typically have three copies of chromosome 21 in each cell, for a total of 47 chromosomes per cell. read more