1. A genetic mutation causes a disease when the the DNA encodes is altered such that it no longer functions properly.

2 Errors during __ _ can cause genetic problems with the resulting germ cells.

3. Down syndrome is caused by three copies of chromosome 21, also known as

21.

4. A silent mutation is a change in the DNA that does not change the encoded

and has no phenotypic effect.

protein

meiosis

trisomy

amino acid or stop codon

Diagnosing genetic conditions can be difficult because, although scientists have identified genes related to specific diseases, often not enough is known about the disease to determine the exact role of a given gene in the disease. In other cases, perhaps no mutation exists on a known gene for a condition, but a mutation occurs on a related gene that also gives rise to the condition. The human genome is vast, with about 24,000 genes. Scientists do not yet understand the roles and interactions of all these genes in human health and disease.

Meiosis is the process by which germ cells—egg cells in females and sperm cells in males—develop. Meiosis causes germ cells to obtain only half the chromosomes of the person. If the chromosomes fail to separate properly and are shuffled improperly into the chromosomes, an egg cell or sperm cell can have either too few or too many chromosomes. Trisomy 21, or Down syndrome, is a developmental disorder in which three copies of chromosome 21 are passed down from the person's mother and father. The word "trisomy" means that there are three copies of chromosome 21, indicating that one of the germ cells did not undergo meiosis properly. This condition affects about 5,000 babies born each year.

In a silent mutation, one nucleotide base in a protein-coding region gets swapped out for another base. However, the resulting three-nucleotide sequence, or codon, encodes for the same amino acid.

Explanation:

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