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Genetics and Evolution
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Worksheet 1 Working out the structure of DNA
Time to Think (p. 8)
1.
In their DNA model, A is paired with T and G with C, giving the DNA molecule
a width of 2.0 nm. In the model, the distance between adjacent base pair is 0.34
nm. One complete turn of the helix has a length of 3.4 nm. All theses values
correspond to the measurements between different chemical groups of DNA
molecule obtained from X-ray diffraction.
2.
Chargaff’s finding suggested that A might pair with T and G with C in DNA.
Franklin and Wilkins provided the data for the arrangement of different
chemical groups in DNA through the study of X-ray diffraction patterns.
Watson and Crick synthesized different data and built a model for DNA
molecule.
3.
Chargaff’s study was not directly concerned with the structure of DNA.
Franklin died before the Nobel Prize was awarded.
4.
The model suggests a mechanism on how DNA replicates itself by breaking the
bonds between the bases. It also provides a mechanism for how genetic
information can be stored in the base sequence of the molecule.
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Genetics and Evolution
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Worksheet 2 Mendel – the first person to study inheritance scientifically
Time to Think (p. 13)
1.
Hypothesis 1: The character not shown in the F1 offspring was destroyed during
inheritance.
Hypothesis 2: The character not shown in the F1 offspring was masked by the
other character.
2.
This result supports Hypothesis 2. If the character is controlled by two factors
and each parent passes only one factor to the offspring, it can explain the 3:1
ratio of the two parental characters in F2.
Time to Think (p. 15)
3.
The F2 plants have different combination of hereditary factors: TT, Tt and tt.
Plants with TT and Tt have tall stems, and plants with tt have short stems.
The figure below shows the ratio of F2 plants with different combination of
hereditary factors.
tall
tall
F1
Gametes formation
Gametes
Fertilisation
F2
Ratio
A genetic diagram showing the cross between the F1 pea plants
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Genetics and Evolution
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4.
The ratio of 3:1 is only a probability which is affected by “chance factors” such
as which gametes will combine with each other during fertilisation and which
offspring will survive.
5.
Hereditary factors are discrete units of inheritance that can be inherited
independently without loss through generations. Blending of parental
characters suggest that parental characters are mixed together in the offspring
and cannot be separated from each other.
6.
Mendel’s idea of inheritance of discrete hereditary factors was too advanced at
his time and there was no supporting evidence for his theory.
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Genetics and Evolution
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Worksheet 3 What did Darwin learn from the finches?
Time to Think (p. 18)
1.
He collected plant and animal specimens from different places, made a record
of his collections and sent some specimens back to England.
2.
The animal and plant species on the Galapagos Islands showed slight but
significant variations from those on the mainland. Those variations were
specific to the species from each island.
3.
They showed different body features specific to each island, such as shapes of
the beak and were adapted for different diets.
Time to Think (p. 20)
4.
The observations that form the basis of Darwin’s theory of natural selection
include: (i) All organisms tend to produce many more offspring than can
survive. (ii) Individuals within a species show variations.
5.
Individuals with favourable features are selected to survive and reproduce by
the conditions of the natural environment.
Time to Think (p. 21)
6.
Darwin did not publish his theory of natural selection at first because he did
not want to face the controversy aroused by his theory which was in conflict
with the biblical account of special creation.
7.
He was prompted to publish his idea when another naturalist, Alfred Wallace,
has also arrived at a theory of natural selection that was similar to his.
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Genetics and Evolution
Answers
Time to Think (p. 22)
8.
Suggested answer: The idea of evolution of organisms are supported by fossil
records, comparative anatomy, amino acid composition of proteins such as
haemoglobin.
9.
(Open-ended answer) One possible answer: The development of strains of
bacteria that is resistant to antibiotics and the development of insect species
that are resistant to inssecticides.
10.
(Open-ended answer) Suggested answer: To some, the evolution of humans is a
scientific view on the origin of mankind; to millions of Christians and Catholics,
the process of creation is acts of God.
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