Multiple Choice
Which of the following processes will most likely produce a human zygote with 45 chromosomes?
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6. Chromosomal Variation
Chromosomal Mutations: Aneuploidy
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Why do relatively few fetuses with chromosomal trisomies survive to birth?
A
Trisomies are typically corrected by cellular repair mechanisms before birth.
B
Trisomies usually result in increased fertility, causing early delivery before full term.
C
The presence of an extra chromosome always leads to enhanced viability and survival.
D
Most trisomies cause severe genetic imbalances that disrupt essential developmental processes, often leading to embryonic or fetal lethality.
Verified step by step guidance1
Understand what a trisomy is: it is the presence of an extra chromosome in the cells, resulting in three copies of a chromosome instead of the normal two.
Recognize that chromosomes carry many genes, and having an extra chromosome causes an imbalance in gene dosage, meaning that genes are expressed at abnormal levels.
Consider how this gene dosage imbalance affects development: it disrupts essential biological pathways and processes that are critical during embryonic and fetal development.
Realize that because of these disruptions, many fetuses with trisomies experience severe developmental problems that often lead to miscarriage or fetal death before birth.
Conclude that only a few trisomies are compatible with life to birth because most cause such severe genetic imbalances that the embryo or fetus cannot survive.
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