Final answer:
A human fetus without both copies of chromosome 1 has monosomy, which is a type of aneuploidy resulting in severe genetic imbalance and typically prevents development to birth.
Step-by-step explanation:
A human fetus missing the two copies of chromosome 1 exhibits aneuploidy, specifically a type called monosomy. Monosomy is a condition where a fetus is missing a chromosome from a pair and has only one copy instead of the typical two. This is a severe genetic imbalance because each chromosome contains vital genes necessary for development and survival. Monosomic zygotes are especially compromised because they lack an entire set of these essential genes, often leading to developmental failure prior to birth.
Down Syndrome, the most common viable form of aneuploidy, is a trisomy where individuals have three copies of chromosome 21 instead of two. It is characterized by certain physical features, developmental delays, and is associated with older maternal age. However, monosomy is generally not compatible with life.