JOHN BAVOSI / SCIENCE PHOTO LIBRARY JOHN BAVOSI / SCIENCE PHOTO LIBRARY
Foetal genetic development. Artwork representing the genetic development of a human foetus. Only the outer part of the foetus is visible, but the hollow inside is being "filled" by chromosomes. Humans have 23 pairs of chromosomes, one chromosome from each pair being inherited from each parent. There is a full compliment of chromosomes in all the foetus' cells, controlling the position and timing of development of the body. The foetus, inside the amniotic sac (blue), is connected to the mother's uterine wall (at bottom) by an umbilical cord (at lower centre). At lower right is the yolk sac (yellow) which supplies nutrients during early pregnancy.
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