gene 3000 - your inner fish CH. 3

chapter 3

Every cell in the body contains…

exactly the same DNA

Cells are different depending on which genes are…

turned off and on

When a gene is turned on, it makes …

a protein that can affect what the cell looks like and how it behaves.

Our limbs exist in 3 dimensions which are:

a top and bottom, a pinky side and thumb side, and a base and a tip

Limbs begin their development as ___ that extend from our ____

tiny buds; embryonic bodies

Which is a good embryo to test limb development?

Chicken eggs

Saunders and Zwilling found that a strip of tissue at the extreme end of the limb bud is…

essential for ALL limb development

If the strip of tissue is removed…

development stops

If the strip of tissue is removed EARLY…

only an upper arm or piece of an arm forms

If the strip of tissue is removed slightly LATER

only an upper arm and a forearm forms

If the strip of tissue is removed even LATER

the arm is almost complete but the digits are short and deformed

What is the patch of tissue that causes the pinky side to be different from the thumb side called?

the zone of polarizing activity (ZPA)

The ZPA controls …

the formation of fingers and toes

Where there is a high concentration of ZPA…

cells will create a pinky

The farther from ZPA

the cells will create a thumb

What gene in flies makes one end of a body segment look different from another?

hedgehog

The researchers found that hedgehog existed in ___ as well and named it ____

chickens; Sonic hedgehog

Sonic hedgehog reacted the same way to ____ as ___

retinoid acid (form of vitamin A); ZPA

In all animals that have been studied, Sonic hedgehog is active in ____

ZPA tissue

The DNA recipe to build _____ was identical in ____

upper arms, forearms, wrists, and digits; every creature that has limbs

Randy Dahn had the idea of ….

treating skate embryos like the chicken egg experiment

Essentially, Dahn wanted to assess whether Sonic hedgehog’s role in limbs is …

unique to limbed animals

Randy found a shark with…

the Sonic hedgehog gene

Sonic hedgehog turns on at the same time in skate fin development as it does in

chicken limbs

The vitamin A caused Sonic hedgehog to turn on ….

in the opposite side of the limb (similar to chickens)

When Randy put in a mouse Sonic hedgehog protein, what did he see?

A response to the protein and activation of it and fingers development on the basis of how close they were to the Sonic hedgehog bead

The great evolutionary transformation….

DID NOT involve the origin of new DNA (much of the shift was from ancient genes)