Wednesday March 31, 1999
Announcements:

Lecture notes:

Fetal growth

Week 8 or 9 through birth the baby is called a fetus.

There is a fine tuning of most organs. "Minor" birth defects develop now.

The face and genital mature during this period.

This is a period of rapid growth. (1/2 of all infant deaths are from low birth weight)

Conception to birth

About 266 days 38 weeks

From 1 cell to 1 million million (yes 1 million million cells) cells.

Estimates are that over 60% of conceptions do not make it to birth. One half of these have chromosome problems:

Mistakes in the genetic code. There are over 3,00 genetic diseases.

Mistakes in gastrulation - Siamese twins: 1 in 100,000 births

Mistakes in organogenesis - 1 in 500 babies are born with neural tube defects.

Three percent of babies born have serious defects.

Events in Development (and areas of problems with development)

Cell division: mutations (genetic abnormalities)

Cell migrations: entire tissues migrate from one site to another. Example: neural tube defects: mistakes result in spina
bifida. Cells move in response to chemical cues and "adhesive" cues.

Controlled cell death: (elimination of tissue not needed in adult) Examples: tissue between fingers and puppies born with
"eyes shut".

Pattern formation: arm vs. leg
upper arm vs. leg
finger vs. toe

Not too many mistakes here in humans.