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In this chapter

(^1919)

Beyond Mendel

chapter

Beyond Mendel

Exploration: Inherited

Traits

Lab Exercise 19.A: Tracing

the Hemophilia Gene

Explore an Issue:

Screening for Genetic

Disorders

Web Activity:

Amniocentesis

Investigation 19.1:

Sex-Linked Traits

Lab Exercise 19.B:

Mapping Chromosomes

Lab Exercise 19.C:

Evidence of Hereditary

Material

Web Activity: Avery and

MacLeod

Web Activity: Elementary,

My Dear Crick

Investigation 19.2:

Isolation and

Quantification of DNA

Explore an Issue:

Competition and

Collaboration Advance

Science

Early scientists believed that hereditary traits were located in the blood. The term “pure

bloodline,” which is still used today by animal breeders (Figure 1), is a reminder of this

misconception, as is the French term Métis conferred by European fur traders on peo-

ples of mixed Aboriginal and European “blood.” Today we know that inherited traits

are determined by genes, which are located along the thread-like chromosomes found

in the nucleus of each cell.

The field of genetics changed quickly once scientists began to describe the location and

the chemical makeup of chromosomes. Genes can now be identified and selected, and

sometimes even altered. One of the most dramatic examples of changing inherited traits

is the production of mice that are smarter than mice are naturally. This genetically mod-

ified strain was dubbed Doogie, after a television character who was a teenage genius.

The modification and insertion of a single gene,NR2B, into a chromosome of the

mice improves the functioning of nerve receptors that play a key role in memory and

learning. The laboratory-bred Doogie mice learn faster and remember more than normal

mice. For example, scientists found that when a new and an old object were introduced

into the cage with the Doogie mice, they spent most of their time exploring the new

object. This indicated that they recognized and remembered the old object. Normal

mice spent equal time with the new and old objects. The Doogie mice generated great

excitement, because humans possess a corresponding gene.

626 Chapter 19 NEL

Answer these questions as best you can with your current knowledge. Then, using

the concepts and skills you have learned, you will revise your answers at the end of

the chapter.

1. In what part of the cell would you find genes?
   2.Can you distinguish males from females by looking at their genetic material?
   3.Explain how a better understanding of chromosome structure could lead to a more
   complete understanding of gene function.
   4.Why might some people be opposed to making mice smarter?
   5.Why might the research with mice prove important for people with Alzheimer’s
   disease?

STARTING Points

Career Connection:

Entomologist