variation
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CHAPTER 14: VARIATION 1
CHAPTER 14 : VARIATION
2.1 Variation in Organisms Activity 1 : Complete the table to compare continuous variation and discontinuous variation
Continuous variation Discontinuous variation
Differences are slight and grade into each other Differences
Slight with intermediate Intermediate
Determined by One or a very few genes
Graph
Normal distributionType of
distribution
Influencing factor Genetic factor
Cannot be inherited Inheritance
Activity 2 : Complete the graphic organizer showing the effects of genetic factors on variation.
1.Genetic recombination by c…………... o…………….
during meiosis
2.Independent assortmentof
c…………………
Random f…………………………
between ovum and any spermMutation
Effects of genetic factors on variation
CHAPTER 14: VARIATION 2
Activity 3 : Match the sequence of events of crossing over during prophase 1.
CHAPTER 14: VARIATION 4
Structured items:1.
TABLE 15.1
Colour of flower Group of Hibiscus
Red A and C
Yellow B and D
TABLE 15.2
(a) What is the type of variation shown by the table 15.3 ?
Trait Type of variation
Height Continuous variation
Colour of flower Discontinuous variation
[2 marks ]
(b) Base from the investigation , what is meant by continuous variation ?
__________________________________________________________-
-__________________________________________________________
[ 1 mark }
Group of
Hibiscus
A B C D
Height range 151-155 cm 156-160 cm 161-165 cm 166-170 cm
Number of tree 6 9 10 5
CHAPTER 14: VARIATION 5
(c)(i) Using results from table 15.1, draw a histogram of number of Hibiscus
tree against the height range (cm).
(ii) Joint the midpoint of each bar to draw a smooth curve .
(iii) Using results from table 15.3 plot a bar graph of number of people against
the ability to roll tongue. [5 marks ]
(d) State the factor that can cause this type of variation for each trait stated.
Traits Factors that cause variation
Height
Tongue Rolling
[2 marks ]
(e) Explain how the students conducted the investigation to determine the
type of variation in the height of people ? [3 marks ]
2.
Features :
* Broad forehead
* Short neck and limbs
* Almond-shaped eyes with folded eyelids
* Thick protruding tounge
* Mental retardation
DIAGRAM 15.3
Diagram 15.3 shows a group of children with a genetic disease due to mutation .
(a) State the genetic disease based on diagram 15.3 . [1 mark ]
(b) What is the type of that mutation ? [1mark ]
CHAPTER 14: VARIATION 6
(a) How many chromosomes do the children have ? [1 mark]
(b) Mutation are caused by agents called mutagens .
Give two examples of mutagens . [2marks ]
( f ) How do mutagens caused mutation ? [2 marks]
( g ) Table 15.4 below shows genetic diseases caused by chromosome mutation.
Fill in the blank by using the word given .
Male Klinefelter’s syndrome Female Jacob’s syndrome
Turner’s syndrome Male and Female
DiseaseNumber of
Chromosomes
Chromosomes
involved Sex
( 44 + XO )Absence of one sex
chromosome
( 44 + XXY )An extra X
chromosomes
TABLE 15.4 [4marks ]
CHAPTER 14: VARIATION 7
Essay Items.
1.
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
2..
Type of
finger
prints
Curves Right Loops Whorl Left Loops
DIAGRAM 15.4
Diagram 15.4 shows different variation among human beings.
(a ) Determine the type of variation in Diagram 15.4 and 15.5. Give the reasons.
[4 marks]
(b) (i) What are the differences between continuous and discontinuous variation?
(ii) State the factors that cause variation in humans .
[6 marks]
CHAPTER 14: VARIATION 8
(c) Base from the statement above, explain the three sources of genetic factors
during sexual reproduction [10 marks]
There are three sources of genetic factors in sexual reproduction events : Crossing over during meiosis 1 Independent assortment during meiosis Random fertilisation
CHAPTER 14: VARIATION 9
ANSWER :2.1 Variation in Organisms Activity 1 : Complete the table to compare continuous variation and discontinuous variation
Continuous variation Discontinuous variation
Differences are slight and grade into each other Differences
Differences are discreet and clear cut
Slight with intermediate Intermediate No intermediates
A large number of genes Determined by One or a very few genes
Graph
Normal distributionType of
distributionDiscrete distribution
Environmental factor Influencing factor Genetic factor
Cannot be inherited Inheritance Can be inherited
CHAPTER 14: VARIATION 10
Activity 2 : Complete the graphic organizer showing the effects of genetic factors on variation.
1.Genetic recombination bycrossing overduring meiosis
2.Independent assortmentof
chromosomes
Random fertilisation
between ovum and any spermMutation
Effects of genetic factors on variation
CHAPTER 14: VARIATION 11
Activity 3 : Match the sequence of events of crossing over during prophase 1.
CHAPTER 14: VARIATION 12
Activity 4 : Name the type of chromosomal mutation.
Type of mutation Name
Deletion
Duplication
Inversion
Translocation
CHAPTER 14: VARIATION 13
Structured items:1.
TABLE 15.1
Colour of flower Group of Hibiscus
Red A and C
Yellow B and D
TABLE 15.2
(c) What is the type of variation shown by the table 15.2 ?
Trait Type of variation
Height Continuous distribution
Colour of flower Discontinuous distribution
[2 marks ]
(d) Base from the investigation , what is meant by continuous variation ?
There is a complete range of measurements for height from 151 cm to 170 cm
[1 mark ]
(c)(i) Using results from table 15.1, draw a histogram of number of Hibiscus
tree against the height range (cm).
Group of
Hibiscus
A B C D
Height range 151-155 cm 156-160 cm 161-165 cm 166-170 cm
Number of tree 6 9 10 5
CHAPTER 14: VARIATION 14
(ii) Joint the midpoint of each bar to draw a smooth curve .
Number of Hibiscus tree
10 8 6 4 2
Height range (cm)
151- 156- 161- 166-
155 160 165 170
(iii) Using results from table 15.3 plot a bar graph of number of Hibiscus tree
against the height. [5 marks ]
Number of Hibiscus tree
14
12
10 Height (cm)
(d) State the factor that can cause this type of variation for each trait stated.
Traits Factors that cause variation
Height Genetic and environmental factor
Tongue Rolling Genetic factor
[2 marks ]
(e) Explain how the students conducted the investigation to determine the type of
variation in the height of Hibiscus tree ? [3 marks ]
-The height of each tree is measured using the measuring tape/ruler.
- The height is grouped into five classes of height range
CHAPTER 14: VARIATION 15
- The height range is recorded in a frequency table.
- A histogram is drawn to show the normal distribution
[ marks ]
2.
Features :
* Broad forehead
* Short neck and limbs
* Almond-shaped eyes with folded eyelids
* Thick protruding tounge
* Mental retardation
DIAGRAM 15.3
Diagram 15.3 shows a group of children with a genetic disease due to mutation .
(a) State the genetic disease based on diagram 15.3 . [1 mark ]
Down Syndrome
(b) What is the type of that mutation ? [1mark ]
Chromosomal mutation
(c) How many chromosomes do the children have ? [1 mark]
47 chromsomes
(d) Mutation are caused by agents called mutagens .
Give two examples of mutagens . [2marks ]
Radioactives radiation , X-rays , ultraviolet light , gamma rays , chemical
substances , formaldehyde , pesticides .
( f ) How do mutagens caused mutation ? [2 marks]
Chromosomal mutation -changes in the structure of chromosomes or the
number of chromosomes.
Gene mutation -Chemical change in the structure of gene, it may also alter
CHAPTER 14: VARIATION 16
the DNA or genetic code.
( g ) Table 15.4 below shows genetic diseases caused by chromosome mutation.
Fill in the blank by using the word given .
Male Klinefelter’s syndrome Female Jacob’s syndrome
Turner’s syndrome Male and Female
DiseaseNumber of
Chromosomes
Chromosomes
involved Sex
Turner’s
syndrome( 44 + XO )
Absence of one sex
chromosomeFemale
Klinefelter’s
syndrome( 44 + XXY )
An extra X
chromosomesMale
TABLE 15.4 [4marks
CHAPTER 14: VARIATION 17
Essay Items.
1.
2.
Type of
finger
prints
Curves Right Loops Whorl Left Loops
DIAGRAM 15.4
Diagram 15.4 shows different variation among human beings.
CHAPTER 14: VARIATION 18
(a ) Determine the type of variation in Diagram 15.4. Give the reasons.
Discontinuous variation.
This is because different people has distinct type of finger print, either curve,
right loop, whorl or left loop. [4 marks]
(c) (i) What are the differences between continuous and discontinuous variation?
Continuous variation Discontinuous variation
Differences are slight and grade into each other Differences
Differences are discreet and clear cut
Slight with intermediate Intermediate No intermediates
A large number of genes Determined by One or a very few genes
Graph
Normal distributionType of
distributionDiscrete distribution
Environmental factor Influencing factor Genetic factor
Cannot be inherited Inheritance Can be inherited
(ii) State the factors that cause variation in humans .
Genetic and environmental factors. [ 6 marks ]
(c) Base from the statement above, explain the three sources of genetic factors
during sexual reproduction [10 marks]
There are three sources of genetic factors in sexual reproduction events : Crossing over during meiosis 1 Independent assortment during meiosis Random fertilisation
CHAPTER 14: VARIATION 19
No. Answer Mark
1(a) -Diagram 15.4 is (height ) continuous variation
-Because the differences between individuals are slight
and can be changed .
-Diagram 15.5 is ( type of fingerprints ) Discontinuous
variation
-Because the differences between individuals are obvious
and cannot be changed
1m
1m
1m
1m
(b)(i)
Continuous variation Discontinuous variation
Differences between
individuals are slightly
with intermediates
There is a complete range
of measurements from
one extreme to the other
for a particular
characteristics.
Differences between
individuals are obvious
There is no gradual
change between two
extremes
2m
2m
(b)(ii) Genetic factors
environmental factors or both.
1m
1m
(c) Crossing over during meiosis
-During prophase I of meiosis, two homologous chromosomes
are paired up in a bivalent.
-The non-sister chromatids break at the chiasma.
-Segment of the chromatids exchange places .
-The exchange of genetic materials between the chromatids
results in new , different genetic combination of genes from the
1m
1m
1m
CHAPTER 14: VARIATION 20
parents.
-The new genetic combination result in variation .
Independent assortment during meiosis
-During metaphase I of meiosis , homologous chromosomes
arrange themselves randomly at the equator.
-The random arrangement and separation of each homologous
pair is independent of one another.
-Independent assortment produces various genetic
combinations in the gametes .
Random fertalisation
-Each gametes has a unique set or combination of genes .
-A male gamete can fertilise any of the female gametes, .
-so, the fertalisation between a male gamete and a female
gamete occurs randomly.
-As a result , a zygote is formed with variety of gene
combination.
-With random fertilasation , variations occur in the offspring.
1m
1m
1m
1m
1m
1m
1m
1m
1m
1m
( Max:
10 marks )