ENVIRONMENTAL VARIATION
Grade 7 Unit 7L.3 - Variation
( Lesson 3 ) ( lesson 3 )VARIATION
Curriculum standards: 7.5.1, 7.5.2
Objectives:
- Know that some features of organisms are inherited while others are determined by their environment.
KEY WORDS:
Variation
Characteristic
Inherited variation
Environmental variation
All living things vary in the way they look or behave.
Variation can be between species or within species.
(So variation is the way in which living things look different from each other. )
Living things that belong to the same species are all slightly different. Genetics, the environment or a combination of both may cause these differences.
CAUSES OF VARIATION: :
1- INHERITED VARIATION:
Why do we look like we do? The answer is because we have inherited our characteristics from our parents.
Siblings are not exactly the same as each other because they inherit different genes from their parents.
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2- ENVIRONMENTAL VARIATION:
The environment is the surroundings and all the things
that may affect the living organism.
In identical twins the genes are identical.
But even identical twins are not completely identical; this is due to environmental factors, like following different diets or living in different places.
Many of the differences between people are caused by a combination of genetic and environmental influences.
EXAMPLES OF VARIATION: :
1. VARIATION IN PLANTS
Plants are affected more than animals by small changes in the environment.
Sunlight, temperature, moisture level and type of soil are factors that will determine how well a plant grows.
A plant grown in sunlight with moderate temperatures will grow much faster than a plant grown with the same temperatures in the shade.
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2. VARIATION IN ANIMALS:
The environment can affect most characteristics like weight and height.
It is usually a combination of genetics and environmental factors that determine how we look and behave.
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There are some characteristics that are not affected by the environment at all: :
1. Eye color
2. Natural hair color
3. Ear lobes
4. Blood group
5. Inherited diseases
WORKSHEETS
Answer the following: :
1- Define variation.
.
2-What are causes of variation?
..
3-Why do brothers and sisters look different than each other?
4-Identify each one of the following characteristics as: Inherited, Environmental, or Both (Inherited and Environmental)
Characteristic
Type
Gender (boy/girl)
Weight
Speech accent
Eye color
Blood group
Skin color
Natural hair color
5- Why do identical twins become different some times?
.
6- The animals shown below live in different parts of a river.
Use this key to identify animals A, B and C.
a Animal A is a
b Animal B is a
c Animal C is a
(tubifexlymnaeaawaterbeetlemayflynymphwaterspiderwaterlouseno tailtail4 pairsmore than 4 pairsno shellshell3 pairsmore than3 pairsno legslegs animal)
Objectives:
- Know that selective breeding can produce organisms with desirable characteristics.
KEY WORDS:
Selective breeding
Desirable
Characteristic
ARTIFICIAL SELECTION :
Human intervention in animals or plant reproduction to ensure that certain desirable traits are represented in successive generations. For example, a fast racehorse, or a cow that produces lots of milk.
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The procedures involved in artificial selection are:
1- Select the organisms with the best characteristics.
2- Breed them using sexual reproduction.
3- Some of the offspring will have inherited some of the desirable features; the best offspring are selected and are bred again.
4- This is repeated over generations until the offspring have all the desired characteristics.
Example of selective breeding:
1- SELECTIVE BREEDING IN PLANTS:
How can we produce a large, tasty strawberry?
The small, but nice tasting strawberry was allowed to breed with the large but tasteless strawberry to produce seeds,
The seeds were allowed to grow.
Some of the new strawberries were large and tasty.
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2- SELECTIVE BREEDING IN ANIMALS:
Can you think why cows have been selectively bred?
To produce lots of milk.
To produce better meat.
1- .
2- .
If a horse breeder wanted a very fast racehorse,
they would choose two parents bred for speed.
Selectively bred organisms may not always produce the desired characteristics.
With plants this can be overcome by producing clones.
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Clones are genetically identical individuals.
In order to produce clones, asexual reproduction is needed.
Many plants reproduce asexually on their own, for example, strawberry plants which produce runners.
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WORKSHEET
A: If you have a farm to produce cows, how do you produce cows with high quality meat and lots of milk?
Choose the bull and the cow that may produce offspring with the desired characteristics.
(Bull (2) with low quality meat (2) ) .
(Bull (1) with high quality meat (1) )
(Cow (3) with high quality meat and produce low amount of milk (3) .) (Cow (2) with high quality meat and produce lots of milk (2) .) (Cow (1) with low quality meat and produce low amount of milk (1) )
I will choose bull number.and cow number.
........... ............
WORKSHEET (Continued)
B: Answer the following; :
1- What is the purpose of selective breeding?
2- Which type of reproduction always produces variation?
3 - If these 2 animals were perfect for their jobs they would have some of the characteristics in the boxes. Your job is to match the animal with the characteristics its owner would like best. Draw arrows to the correct animal.
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