Biology Gr10
Name:____________________
Grade 10 Science Related Reading/Biology
Class:____________________
Date:____________________
Inheritance and
Variation
Read the passage below. Then answer the questions that
follow.
Variation
All people are human. They belong to the same species. Your friends and
classmates may have different eye colour and hair colour. Some will be
boys and some will be girls. Some will be tall and some will be shorter. The
presence of differences between living things of the same species is called
variation caused either by genetic differences or by the effect of
environmental factors on the expression of the genetic potentials. Variation
may be shown in physical appearance, metabolism, fertility, mode of
reproduction, behavior, learning and mental ability, and other obvious or
measurable characters.Some of the features of the different organisms in a
species show continuous variation, and some features show discontinuous
variation.
Vocabulary
Highlight the
main vocabulary
terms.
Write these terms
in your notebook
Reading Check
Define variation.
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For any species a characteristic that changes gradually over a range of
values shows continuous variation. Continuous variation is variation that
has no limit on the value that can occur within a population. A line graph is
used to represent continuous variation. Different alleles for one gene have
small effects. Some examples of continuous variation are height, weight,
heart rate, finger length, leaf length and foot length. Human height is an
example of continuous variation. Height ranges from that of the shortest
person in the world to that of the tallest person. Any height is possible
between these values. So it is continuous variation. If you record the heights
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Grade 10 Science Related Reading/Biology
of a group of people and draw a graph of your results, it usually looks
something like this:
The more people you measure, and the smaller the categories you use, the
closer the results will be to the curved line. This shape of graph is typical of
a feature with continuous variation. Weight and foot length would give
graphs similar in shape to this.
A characteristic of any species with only a limited number of possible
values shows discontinuous variation. Discontinuous variation is variation
that has distinct groups for organisms to belong to. A bar graph is used to
represent discontinuous variation. This is where different alleles for one
gene have a large effect on the phenotype.
Some examples of
discontinuous variation are tongue rolling, finger prints, gender (male or
female) and blood
groups.
Human
blood group is an
example
of
discontinuous
variation. There are
only 4 types of
blood group. There
are no intermediates
or other possibilities;
you are either A, B,
AB or O. and there
are no values in between. So this is discontinuous variation.
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Looking
closer
Try to find a proper
definition for these
scientific expressions:
Gene – phenotype
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Grade 10 Science Related Reading/Biology
Some variation within a species is inherited, and some variation is due to the
environment. Variation in a characteristic that is a result of genetic
inheritance from the parents is called inherited or genetic variation.
Children usually look a little like their father, and a little like their mother,
but they will not be identical to either of their parents. This is because they
get half of their inherited features from each parent. Each egg cell and each
sperm cell contains half of the genetic information needed for an
individual. When these join at fertilisation a new cell is formed with all the
genetic information needed for an individual. Some examples of inherited
variation in humans are eye colour, hair colour, skin colour and lobed or
lobeless ears. Gender is inherited variation too, because whether you are
male or female is a result of the genes you inherited from your parents.
There are several causes for genetic variation being present within a
population:
1. Each gene has different alleles. Therefore, different individuals may
have different alleles.
2. During meiosis, chiasmata (crossing over) occurs whereby sections
of DNA are swapped between sister chromatids.
3. During meiosis, there is independent assortment of the homologous
pairs of chromatids.
4. Mutation - gene and chromosome.
5. Random fertilisation.
Characteristics of animal and plant species can be affected by factors such
as climate, diet, accidents, culture and lifestyle. For example, if you eat too
much you will become heavier, and if you eat too little you will become
lighter. A plant in the shade of a big tree will grow taller as it tries to reach
more light. Variation caused by the surroundings is called environmental
variation. Some other examples of features that show environmental
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Critical
thinking
Make a list of
physical traits that
you think are
influenced
by
genes.
Then, write next
to
each
trait
whether you think
it is continuous or
discontinuous.
Grade 10 Science Related Reading/Biology
variation are your language and religion and flower colour in hydrangeas these plants produce blue flowers in acidic soil and pink flowers in alkaline
soil.
Some features vary because of a mixture of inherited causes and
environmental causes. For example, identical twins inherit exactly the same
features from their parents. But if you take a pair of twins, and twin 'A' is
given more to eat than twin 'B', twin 'A' is likely to end up heavier.
SKILL: READING EFFECTIVELY
Read each question, and write your answer in the space provided.
1. What controls inherited traits?
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2. What are the major sources of genetic variation?
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3. Widow’s peak is a human trait which causes a V-shaped hairline
instead of the straight normal one. Predict to which type of
variation this trait does belong.
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Grade 10 Science Related Reading/Biology
4. In the table provided below, compare between continuous and
discontinuous variation.
Continuous variation
Discontinuous variation
5. Why was the trait of human blood grouping categorized as an
example of discontinuous variation?
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6. In your own words, what is the meaning of the term allele?
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7. List some of the environmental factors that can affect the
characteristics of humans.
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Grade 10 Science Related Reading/Biology
8. Describe the influence of environment on Hydrangeas flowers as
mentioned in the text.
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In the space provided, write the letter of the term or phrase that best
completes each statement or best answers each question.
______ 1. Which of the following is an example of genetic variation?
a. Two children have different eye colors.
b. One person is older than another.
c. One person has a scar, but her friend does not.
d. Todd eats meat, but his brother Rod is a vegetarian.
_____ 2. Which of the following is an example of environmental
variation?
a. Apu is a tongue roller, but his brother Sanjay is not.
b. Marge dies her hair blue.
c. Homer inherited baldness from his father's side of the
family.
d. Patti and Selma have hanging ear lobes
_____ 3. Which of the following is not a source of variation in a
population?
a. Inherited genetic differences.
b. Differences due to health.
c. Differences due to age.
d. None of the above.
_____ 4. The genetic material must show variation. Which of the
following is NOT an example of genetic variation?
a. New mutations can occur during meiosis.
b. Different species have different numbers of
chromosomes.
C. Different individuals within a species have different
phenotypes.
d. Individuals of different species may have similar
phenotypes.
_____ 5. Which of the following is NOT a source of genetic variation?
a. Independent assortment of chromosomes
b. Crossing-over
c. Mutation
d. Mitosis
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