Download Science 4th primary 2nd term unite1 lesson 2 Lesson 1: The main

Science 4th primary 2nd term unite1 lesson 2
6 – avoid
dangers
Lesson 1:
The
importanc
e of
levers
The main principles of hereditary
Introduction:
What’s the reason for similarities of traits between family members?
 Genes are transferred from a generation to the next & the genes affect the
traits of organisms.
Key term;
 A trait is a distinct physical characteristic of an
organism which is inherited ( got from the parents)
or acquired ( determined by the environment ).
Example;
 Eye color
 The color of the skin
 The number of fingers
 Blood groups
 The gene is heritable unit which is a portion of the chromosome.The gene
influences the trait.
 The chromosome is a compact string of DNA.
Mendel’s experiment:
Gregor Mendel is the founder of heredity he conducted experiments on pea plants
because :
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Ms. Marim
Science 4th primary 2nd term unite1 lesson 2
a- Pea plants are grown fast & easily.
b- Their life cycle is short.
c- Their flowers are hermaphrodite ( either male or female). Flowers can be self
pollinated or artificially pollinated by man.
d- They produced a large crop.
e- Peas have different types with different traits, so comparison between
them is clear. For example a type has long stem & another has short stem.
A type with white flowers & another with purple ones. The pods of one pea plant
are
green while another type has yellow pods.
Mendel’s experiment with pea plants to study the seed colors.
1- Pea plants that produced yellow seeds were self pollinated for few generations to
ensure a pure trait. The same was done to the type with green seeds.
2- The seeds that resulted were then planted. When their flowers appeared,
Mendel removed the stamens before the anther matured.
3- Mendel used cross pollination between a plant which produces green seeds &
another which produces yellow seeds, then he covered the pistils to prevent further
pollination.
The results of Mendel’s experiments were as follow:
green
Yellow
parents
First generation
yellow seed peas
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Second generation
Science 4th primary 2nd term unite1 lesson 2
Observation:
st
 All the seeds of the 1 generation were yellow.
 Green color disappeared.
 Therefore yellow is the dominant trait while green is the recessive trait.
When the first generation plants were allowed to self pollinate, they produced the
second generation where ¼ had green seeds & ¾ had yellow seeds.
-The dominant character appears in all the individuals of the first generation .
-The recessive trait disappears in the individuals of the first generation & appears in
the second generation.
The same procedure was used to study other traits such as long stems versus short
stem ....etc.
Mendel chose 7 characters & concluded the dominant & recessive trait.
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Ms. Marim
Science 4th primary 2nd term unite1 lesson 2
Mendel concluded the following from the observations he got:
 Traits are transmitted from parents to offspring by means of
hereditary factors now known as genes.
 Each trait has 2 factors (genes) one gene is inherited from the father
& the other is inherited from the mother. If both genes are similar, the
trait that appears is pure.
 When the 2 genes responsible for a certain trait are different this
results in an impure trait (the person that has the trait is a hybrid).
 During meiosis, gametes are formed. Each gamete has only one gene for
a certain trait.
Mendel’s laws of inheritance:
1. The law of segregation:
Mating 2 individuals with contrasting traits results in
the appearance of the dominant trait alone in the first generation.
In the second generation both traits appear & the ratio between
the dominant trait & the recessive one is 3:1
Segregation of Alleles
During gamete formation, alleles segregate from each other so that each gamete carries only a single copy of each gene. Each F1 plant produces
two types of gametes—those with the allele for tallness and those with the allele for shortness. The alleles are paired up again when gametes fuse
during fertilization. The TT and Tt allele combinations produce tall pea plants; tt is the only allele combination that produces a short pea plant.
Using symbols to represent the results of Mendel’s experiments:
C : symbol of the dominant yellow color, small c symbol of the recessive green
color.
CC : a pure dominant trait.
cc : represents a pure recessive trait.
cc
C
1st filial generation
( F1)
X
c
C
Parents
c
(P)
(G)
Cc yellow
hybrid seeds
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CC
Gametes
Science 4th primary 2nd term unite1 lesson 2
Now 2 individuals from the 1st generation pollinate as follows:
Parents
(P)
C c
c
C
C
Gametes
c
x
C c
(G)
2nd filial generation (F2)
CC
Cc
cc
Cc
Pollinating 2 pea plants with different flower colors.
Yellow seeds
Green seeds
( contrasting trait).
Purple flowers are dominant while white flowers are recessive.
PP purple
Parents
P
x
pp white
Gametes
P
p
p
Pp
1st filial generation (F1)
Two hybrid plants from the 1st generation mate as follows
Parents
P
p
PP
Pp
P
Pp
Purple
flowers
hybrid purple
X
Pp
hybrid purple
Gametes
p
pp
5
Pp
White
flowers
Ms. Marim
Science 4th primary 2nd term unite1 lesson 2
Mendel’s 2nd law: The law of independent assortment of
hereditary factors
Mendel conducted a mixed pollination between :
parents
Long stem & purple
flowers
2 dominant traits
First generation
Second generation
Short stem & white flowers 2
recessive traits
with
All plants had purple flowers & long stems
9 long stem &
3 long stem &
3 short stem
purple
white flowers
& purple
flowers
flowers
1 short stem
& short
flowers
Conclusion :
1- The ratio between the dominant trait & the recessive trait is 12:4 = 3:1.
2- Each trait is inherited independently of the other.
During gamete formation , the segregation of the alleles of one allelic pair is
independent of the segregation of the alleles of another allelic pair, therefore
when 2 individuals with 2 contrasting traits mate , the traits of each pair is
inherited independently & appears in the 2nd generation in a ratio 3:1
Enriching information :
The inheritance of some traits don’t follow Mendel’s laws, these are non. Mendelian
hereditary .
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Ms. Marim
Science 4th primary 2nd term unite1 lesson 2
An activity:
Mixed pollination between:
Smooth yellow seeds pea plants
+
wrinkled , green seeds pea plants
Dominant
traits
Recessive
traits
Observations:
1. In the first generation, pea plants had the dominant traits only ( smooth & yellow
seeds).
2. First generation produce the following gametes .
YR
, Yr , yR , yr
3. The second generation plants produce smooth shaped yellow seeds : wrinkled
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yellow seeds : smooth & green seeds : wrinkled & green seeds.
3
:
4.
:
3
1
The ratio of green seeds to the yellow in the
second generation is 12:4
3:1
5.
6.
The ratio of smooth seeds to wrinkled ones in
the second generation is also
12:4
3:1
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Ms. Marim
Science 4th primary 2nd term unite1 lesson 2
Some dominant & recessive traits which appear in humans & follow Mendelian
hereditary laws :
Dominant trait
Recessive trait
1- The ability to roll
the tongue
Can’t roll tongue
2- Separate ear lopes
Connected ear lopes
3- Wide eyes
Narrow eyes
4- Curly hair
Straight hair
5- Presence of dimples
Absence of dimples
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Ms. Marim
Science 4th primary 2nd term unite1 lesson 2
6- A face without freckles
A face with freckles
7- Brown eyes
Colored eyes
Mutations
During DNA duplication, mistakes in DNA replication can occur, the base sequence
of the newly formed DNA differs from base sequence of the original DNA.
The change in the nucleotide sequence of DNA molecule is called mutation.
Mutations disrupt the gene & therefore disrupts an important cell function.
The change in the
chemical composition of
genes
Change in hereditary traits.
Mutations
Beneficial & transmitted to the offspring,
Harmful: causes cancer or
therefore they’re a source of genetic
deformation of newly born or
variation.
An example
ofplant’s.
a new trait that appeared
in a (These
sterility
of some
Light mutations
fur evolved toare
help rare.)
beach
species:
Grey mice have a gene that enables them to make a
protein called melanin which is the pigment that gives
the fur its color.
A mutation occurred which disrupted the formation of
melanin. The result was appearance of a new trait : light
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mice survive on white sand
dunes, while darker fur help
mainland mice survive in fields.
fur.
Ms. Marim
Science 4th primary 2nd term unite1 lesson 2
1- Spontaneous mutations are caused by
 Exposure to radiation : X ray , atomic radiation.
 Exposure to chemicals.
 Exposure to high or very low temperature.
Spontaneous
mutations
variation in
traits
if they ’re
inherited may
lead to a varied
species
2- Induced mutations are caused by human to get genetic variation in plant &
produce desirable traits such as : bigger fruit with better tastes & without
seeds.
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