Download Answer all the questions Time allowed : 49 minutes 1. State two

Buddhist Chi Hong Chi Lam Memorial College
P. 1
A. L. Bio. Revision Test ---- Genetics & Evolution
Answer all the questions
Time allowed : 49 minutes
1. State two factors other than genotype which could affect the characteristics of an offspring ?
[2 marks]
2. DNA is an excellent medium to carry hereditary information as it is stable but changeable.
(a) What is the advantage of DNA being stable ?
[2 marks]
(b) Describe the structure of DNA and how the structure confers stability to the molecule.
[7 marks]
(c) What mechanisms may be involved in changing the DNA molecule ?
[4 marks]
3. Deep sea animals usually have degenerated vision. Explain this in terms of the modern
theory of evolution.
[6 marks]
4. The diagram shows the inheritance of Huntingdon’s chorea in a family.
Symptoms of Huntingdon’s chorea usually develop between the ages of 35 and 40. What is
the chance that individuals G and H will develop Huntingdon’s chorea whereas this is an
dominant disease.
Explain the reasons for your answer as fully as you can. You may use genetic diagrams if
you wish.
[6 marks]
Total : 27 marks
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THE END
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Buddhist Chi Hong Chi Lam Memorial College
P. 2
A. L. Bio. Revision Test ---- Genetics & Evolution
Quest.
1.
Suggested solution
Marks
Nutritional status of mother during pregnancy / Radiation e.g. X-rays / Drugs e.g. alcohol, tobacco
< any 2 or other reasonable examples >
1x2
Sub-total :
2(a)
2(b)
2(c)
Individual cells of a multicellular organism can work in a co-ordinated manner. Any change in the DNA
constituent upsets this harmony.
The stable nature of DNA enables the perpetuation of a species.
Each DNA molecule is formed from two complementary polynucleotide chains running anti-parallel to
each other.
In a polynucleotide chain, adjacent nucleotides are joined together by phosphodiester bridges .
A phosphate gro up, a deoxyribose and a nitrogenous base join together to form a nucleotide.
Projecting out from each deoxyribose molecule is a nitrogenous base.
The nitrogen base of one polynucleotide pairs with a complementary base on the opposite strand.
Purines always bond to pyrimidines, e.g. G to C and A to T.
Features contributing to DNA stability :
Adjacent nucleotides are liked by phosphodiester bonds which are strong covalent bonds.
The total attractive force which results from hydrogen bonding between the paired bases of two
polynucleotide chains is strong and holds the two chains together.
The two chains are helically coiled around each other.
max.:
Mutation may occur spontaneously,
or be induced by chemicals (e.g. colchicines ), radiations (e.g. X-rays and UV) and biological factors
(e.g. viruses).
<any 1>
Mutation may involve
change in the number of chromosomes, e.g. polyploidy
changes in chromosome structure,
changes in DNA structure
Sub-total :
3.
4.
.
Variation in a species can arise through gene mutation,
random assortment and crossing over at meiosis.
Thus in a deep sea environment fish may have good vision, degenerated vision but with alternative
forms of sense.
More offspring are produced than the environment can support, which lead to struggle for existence
among different varieties.
The environmental pressure selects for those individuals that exhibit alternative forms of sense other
than vision and
against those that have good vision which is useless in the dark environment, i.e. natural selection.
Individuals that have more adaptive features (degenerated vision but with alternative sense organs ) are
able to survive the environment
and pass on their characters to their offspring, i.e. survival of the fittest.
Therefore deep sea organisms tend to have degenerated vision.
2
1
1
1*
1*
1*
½*
½*
1*
1*
1*
1*
7
½
½
1
1
1
13
1*
1½ *
½*
1*
½*
1*
½*
1*
Sub-total :
6
Sub-total :
½ ,½
1
1
1
1
1
6
G : 50 % ; H : 0%
Since Huntingdon’s chorea is dominant, so C must be homozygous recessive.
Then D must be heterozygous since his father is normal.
Therefore G have ½ chance to be heterozygous.
Both parents of H are homozygous recessive,
therefore H must also be homozygous recessive.