Thames & Kosmos Genetics & DNA handleiding

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Thames & Kosmos

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Handleiding

It isn’t quite this simple, but let’s assume

that human eye color is controlled by a sin-

gle program and that each of us has two

copies of the program. How could there be

blue-eyed children in a family that other-

wise only has brown-eyed members?

HERE’S HOW

The white chips represent the program for

blue eyes, and the red ones for brown

eyes. The program for brown eyes

dominates the program for blue eyes in

humans. If even one brown eyes program

is present, the result will be brown eyes.

1. Assemble all the possible eye color

program combinations that can occur

with all possible parents. Think about

the combinations that may occur.

2. On the inheritance worksheet, you will

ﬁnd all possible combinations indicated

in the six large blue boxes. Place one

chip combination after the other in the

grid located at the top of the sheet. You

know how to do this from Experiment 8.

3. Following each combination, enter the

result into the appropriate blue box. To

Browned-eyed

parent, blue-

eyed child

YOU WILL NEED

→ colored plastic chips

→ inheritance worksheet

→ red felt-tip pen

Only if both parents carry at least one

hidden copy for blue eyes can the

feature appear in the offspring. As soon

as just one parent has two copies of the

brown eyes program, a spouse with blue

eyes can do nothing to pass that feature

on to the children. (Maybe the

grandchildren though.) The actual

inheritance of eye color in humans only

roughly follows this pattern. In reality,

there are extra programs involved.

A single program is not enough to

develop and control a living being.

Instead, thousands are required.

Researchers do not yet know the exact

number. For humans, one of the most

recent estimates is 20,000 to 25,000

individual programs. Each of us has two

copies of each, resulting in double that

number for the whole set. Half of the

programs come from the mother, the

other half from the father.

Many programs are passed on

independently to the offspring. This

means that “blue eyes” can be combined

with “big feet,” or “blue eyes” with

“small feet,” or “blue eyes” and “big

feet” with “big ears.” There is a vast

number of possible combinations.

→

WHAT’S HAPPENING?

do that, simply color in the white disks with

the red felt-tip pen. You already know that

the program for brown eyes dominates the

program for blue eyes. Now enter the

number of children that would have blue

eyes and the number that would have

brown eyes into the little boxes on the

right side of the sheet.

You will ﬁnd the solution on page 47.

→ → →

18 | Heredity: Investigating Traits

EXPERIMENT 9

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