OnlineHS: Biology AUnit 4: Evolution

6 week human embryo photo from: http://medlibrary.org/medwiki/Embryos

DevelopmentalBiologist

Developmental Biologists are scientists who study the stages of growth ad development that living organisms pass through as they grow from fertilized egg to mature adult and beyond.

“Developmental Biologist” Defined

Access the “Developmental Biologist Interview” by clicking on the hypertext link within the course.

Read the interview. Take notes in your journal How would you explain

the job of this scientist?

Developmental Biologist Interview

Embryology Defined Embryology is the branch of

developmental biology that focuses on the early development of organisms before they are born or hatched.

During this prebirth or prehatching stage, scientists call the developing organisms embryos.

Scientists can compare developing embryos of organisms as diverse as fish, amphibians, reptiles, birds, and mammals.

They find that the embryos of these vertebrate animals (animals that have backbones) resemble each other.

Tree Frog Embryos From: AccessScience.com

Online: Embryo Interactive

Visit the PBS/NOVA interactive web site: Guess the Embryo

http://www.pbs.org/wgbh/nova/evolution/guess-embryo.html

Observe Darwin’s early drawings.

What animals are they?

Observe

Hint: You are looking at stages in the development of a lizard, pig, human & tortoise.

Who is who??

Observe

HumanPigTortoiseLizard

Which organisms have embryonic stages that are the most similar?

Least similar? Why?

HumanPigTortoiseLizard

Record in Your Journal

What do you think these similarities and differences tell scientists about how these organisms have changed across time and how they are related?

Consider whether you expect related organisms to look similar or not. Would you also expect related organisms to go through similar stages of development?

Consider later stages of development. Do the more closely related organisms look more or less similar?

In Your Journal - continued

Form vs. Function How has technology added to our

understanding of Developmental Biology?

In current biology, fundamental research in developmental biology and evolutionary developmental biology is not driven anymore by morphological (shape) comparisons between embryos, but more by molecular biology.

This is partly because Haeckel's drawings were very inaccurate.

Read more at:http://en.wikipedia.org/wiki/Embryo_drawing

Drawings of embryos published 123 years ago by German biologist Ernst Haeckel

DNA Evidence From the course hypertext link,

access the assignment “DNA Comparison Worksheet”

Write the questions at right and complete entry in your journal with the answers to each.

What does DNA stand for? What does DNA code for? What important proteins occur in

the blood and what is their function?

Are humans the only ones that have these proteins?

What causes the differences in the same proteins found in different organisms?

What do similarities in two different organisms DNA for the same protein suggest?

Compare DNA Worksheet Find and count

(use a colored pencil/marker)

The matches The mismatches.

Example: Match Mismatch

Use the DNA comparison math work handout to assist you in finding the percent similar.

Do the Math

Embryonic Development

Minor modifications in the timing and ordering of events during embryonic life can produce enormous differences in adults.

Embryonic Development

The intriguing point is that among all the millions of animal species alive today, there are only a couple of dozen really different body-part tool kits.

Every vertebrate has a backbone and four limbs, while arthropods have exoskeletons and jointed appendages

Variations in Development What happens when

there is a variation in embryonic development?

Atavism While humans normally only

have tails as embryos occasionally children are born with tails still intact.Similar pictures can be found in medical textbooks.

Usually the tail is just soft tissue but occasionally children are even born with tails that have extra vertebral bones in them.

The re-expression of an ancestral character is known as an atavism

More info- Google: “Chandre Oram”

Atavism Four-year-old Chinese girl

Jiaxue, who suffers from hairy black moles, sits on a bed at home November 4, 2006 in Changchun of Jilin Province, China. Jiaxue was born with black moles covering part of her back, breast, neck and face. Experts said the condition may be an atavism.

Source: LIFEhttp://www.life.com/image/72406679

Vestigial vs. Atavistic Many traits no longer give organisms benefits in terms of natural

selection, but these traits can still exist, as long as they don't harm the organism.

Every organism carries traits that are of no use to it. The traits are called vestigial.

Humans, having descended from creatures with tails, still have tailbones within their skeletons.

Many plants that once reproduced sexually (requiring pollination) evolved to reproduce asexually, yet they still produce unnecessary flowers.

Sometimes, a mutation causes a vestigial trait to express itself in a more pronounced way. Scientists refer to this as atavism.

Examples are humans born with small tails, or whales with hind legs.

You should be able to: Explain how comparing the development of embryos

contributes to the understanding that organisms have changed over time, but may be related.

Explain where DNA is located, its purpose, & function. Give an explanation of a DNA comparison from different

primate species. Includes which primates are most similar and which are most different.

Explain distinctive research methods of this field and explain how research explains change over time.