� Chapter 2- Unity of Life �
2.1 Heredity & Chromosomes
2.1.1 Heredity
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Heredity: the passing on of certain inherited characteristics from one generation to
another
All offspring are similar to their parents in terms of
○ Morphological structures
○ Physiological functions
Living things can pass on their traits from one generation to the next
Discrete phenotypic traits (obvious, observable, measurable trait)
Trait
Dominant
Recessive
Eye
Wide
Narrow
Length of index finger
Index shorter than ring
Ring shorter than index
Hair
Curly & black
Straight & light
Dimples
Dimples
No dimples
Upper eyelid
Double eyelid
Monolid
Tongue
Ability to roll
Inability to roll
Ear lobe
Free
Attached
Eye color
Black
Colored
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Dominant traitRecessive trait
appears if contributed by a dominant allele
- present at the gene level but is masked
- does not show in organism
2.1.2 Chromosomes
1. Hippocrates (Greek medical scientist)
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There was a substance [sperm] in semen that can cause women
to be pregnant
2. Hamm (17th century)
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Discovered tiny bodies in semen (with microscope)
People believed- a miniature man (homunculus) lived in the sperm
○ Fertilized egg (combination of sperm & ovum) -caused
offspring to possess traits from parents
� Individuals of the same species have almost the same number of
chromosomes & morphological structures
� Individuals of different species have different number of
chromosomes & morphological structures
Humans have
23 pairs (46) of
chromosomes
1. Mitosis
-process of: During cell division the genetic material of eukaryotic cells being duplicated and
distributed
● Every chromosome will replicate to form 2 identical ones, which will align at the centre of
the cell
● 1 parent cell divides into 2 daughter cells
● Each daughter cell has 2 pairs of chromosomes (same as parent)
● After mitosis, number of chromosomes in daughter cell remain the same as the mother
cell
Two daughter
Mother cell
Cell
2. Meiosis
- During sexual reproduction in eukaryotes,
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━cell division to produce gametes
Chromosomes replicate once and divide twice consecutively
Produce 4 daughter cells
Number of chromosomes in gametes is halved
3. Fertilization
-male & female gamete fuse to form a zygote (fertilized egg)
● Zygote become a new individual by mitosis
● Zygote is formed from fusion of sperm & ovum
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∴ Half the chromosome comes from the father (paternal origin)
Another half from the mother (maternal origin)
○ Cells of new individual contain chromosomes of father and mother
Living things maintain the number of chromosomes as they reproduce from one generation to
another through the processes of mitosis, meiosis, fertilization.
2.2 Determination of Traits
2.2.1 Determination of Sex
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Number of chromosomes in the human somatic cell (body cell) is 46 (23 pairs)
Each pair comes from the father & mother respectively
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Sex chromosome (23rd)━ type of chromosome that participates in sex determination
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23rd pair of chromosome
○ Male- XY
○ Female- XX
Figure Reading (pg 26)
1. (From perspective of sex chromosomes) How many types of sperms?
● 2
2. What are the different types of sperm cells?
● X and Y [female & male]
3. What about female sex chromosomes?
● XX
X
X X
OVUM \ SPERM
22+X
22+Y
22+X
44+XX
44+XY
22+X
44+XX
44+XY
X
4. How many combinations of sex chromosomes can be formed?
● 2
5. What are the combinations?
● XX,XY
6. What is the probability of giving birth to a boy or a girl?
● 1/2
7. Write down the sex chromosomes
a. Male: XY
b. Female: XX
X
X Y
X
2.2.2 Gene & DNA
1. Gregor Johann Mendel (Austrian geneticist)
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(1856) Hypothesized━ the genetic substance that affects the traits in the pea plant
was the heredity factor
Discovered the basic principle of heredity
2. Wilhelm Johannsen (Danish (Denmark) geneticist)
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(1909) Proposed━ concept of genes
✧ genes record & transmit genetic information
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Proposed distinction between genotype & phenotype
3. Thomas Hunt Morgan (American (US) geneticist)
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Studied genetic traits of fruit flies (Drosophila)
✧ genes are arranged in linear form on chromosomes
✧ genes are the mechanical basis of heredity
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∴ chromosomes are carriers of genes
4. James Watson(American scientist) & Francis Crick
(British
Scientist)
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Proposed━ double helix model of DNA
(deoxyribonucleic acid
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Proved━ DNA is the genetic material passed down
heredity
through
1. DNA
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large molecular compound with relative mass ranging millions
● made up of 2 long chains twisted in spiral form (double helix structure)
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every chromosome contain ━a molecule of DNA
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Each DNA contains ━ many genes
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Carriers of genes
Cell
Chromoso
me
2. GENE
� affect synthetsis of proteins
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∴ control traits of living things
� carried by chromosomes
2.3 Variation
-difference between individuals of the same species
2.3.1 Types of Variation
1. Non-Heritable Variation
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Caused by environmental factors
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Genes━ not changed
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Traits━ not inherited by next generation
2. Heritable Variation
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Caused by change of genetic materials
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Traits━ inherited by next generation
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e.g. albinism
Nucle
us
X
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Chromosomal Mutation
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A change in the number of chromosomes
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can be passed to the next generation
Effects of Chromosomal Mutation
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change in number of chromosomes can produce a new species
e.g. Horse (64 chromosomes) + Donkey (62) = Mule (63)
change in number of chromosomes can produce a new trait
● hereditary diseases can be caused
e.g. Down’s syndrome (trisomy-21) cause by extra chromosome 21
[mentally retarded, susceptible to diseases]
Gene Mutation
� A change on a section of the DNA molecule
� Original genes replaced by new mutant gene━ causing subsequent generations to have
traits that were not observed in their ancestors
Effects of Gene Mutation
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most genetic mutations are harmful to living things
Example 1━ Sickle-cell anaemia
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Red blood cells are sickle-shaped━ due to changes in genes that control synthesis of
haemoglobin
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Leads to changes in molecular structure of haemoglobin
Example 2━ Albinism
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Do not cause much impact on living things
Caused by mutation in synthesis of melanin (lack of melanin)
Gene Mutation in Human
➔ Happen either naturally or by environmental factors
➔ Mutagens raise the probability of genetic mutation
➔ e.g. 1. Physical factors
● X-rays
● Lasers
● Ultraviolet rays
● Radioactive rays
➔ 2. Chemical factors
● From nitrites & aflatoxin
➔ Biological factors
● Virus
● Bacteria
Advantageous Mutation
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important role in survivability & reproductivity of organisms
If living things do not have variations,they cannot adapt to changes in environment
new breeds produced
variation━ fundamental factor for diversity in living things
Advantageous Mutation in Agriculture
e.g. Selective Breeding
❖ Best-desired quality cows are interbred━ giving rise to a new breed that can produce high
beef quality or milk quality
❖ Methods to attain a new breed of prime quality:
● Irradiation
● Chemical treatments
● Space Breeding
Space Breeding
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Technique of sowing seeds into space on a recoverable satellite or spacecraft
Returning to Earth, mutant seeds will be selected and planted to breed strains with
desirable traits
2.3.3 Transgenic Technology
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Application of scientific techniques in extracting desirable genes from an organism and
inserting them into another organism
� New gene is recombined with original genes of 2nd organism━ changes the traits
� The core technology in genetic engineering
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Agriculture crops using transgenic technology possess quality traits
e.g. genetically modified soybeans━ resistant to herbicides
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Will not be exterminated with weeds
Farming cost reduced
Genetically Modified Food (GM food)
❖ Effects on environment & human health still highly debated
❖ Can improve quality of life
❖ Uncertainties in terms of food safety
➢ May bring undesirable effects in the long run
2.3.4 Unity of Life
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Organisms exist in countless shapes & sizes, however they have things in common that
show the unity of life
� Genetic materials of all organisms appear the same
● All have cells as building blocks (cells are basic units of structure & function)
� Living things contain about 30 types of elements
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Core
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elements:
Carbon
Hydrogen
Nitrogen
Oxygen
}
make up 90% of body of living things
Proteins━ compounds that make up various life forms & enable life functions to be done
● e.g. conversion of energy & matter need enzymes as catalysts
○ Most enzymes are proteins
� External:
● Respiration
● Photosythesis