Summative Practice Chapter 12 (Form 5 Biology Textbook Exercise and Answer)


Question 1:
Tables 1.1 and 1.2 show data that were collected for two different characteristics from 35 pupils in Form 5 Bunga Raya.


(a)(i) State the types of variation for body mass and types of earlobes.
(a)(ii) State two differences between body mass variation and types of earlobes variation.

(b) Figure 1.1 shows a karyotype of an individual who has a genetic disease caused by mutation.


(i) State the disease shown in Figure 1.1.
(ii) Which type of mutation causes the disease stated in 1(b)(i)?
(iii) Explain how the type of mutation in 1(b)(ii) causes the disease.

(c) The statement below describes trees of the same species planted in two different plots, X and Y on a farm.


The plantation was infected and all trees in plot X were killed whereas only part of the plants in plot Y died of the infection. Explain why all the plants in plot X were killed.


Answer:
(a)(i)
Body mass: Continuous variation
Types of earlobes: Discontinuous variation

(a)(ii)

(Any two characteristics)

(b)(i) Down syndrome

(b)(ii) Chromosomal mutation

(b)(iii)
Failure of chromosome 21 to separate during meiosis / occurrence of nondisjunction of chromosome 21. It produces two chromosome 21 in one gamete. When this gamete is fertilised by a normal gamete, a zygote with three chromosome 21 is formed.

(c)
Trees in plot X are produced from tissue culture / cloning. Therefore, all trees have the same characteristics as their parent. Clones do not show variation in terms of genetics. They have similar resistance towards a disease. If there is an infection, all clones will be wiped out because they cannot survive the disease.


Question 2:
(a) Figure 2.1 shows patterns of a few thumbprints.


Identify the types of variations for the thumbprint pattern and discuss the factors that cause these variations.

(b)(i) State the difference between gene mutation and chromosomal mutation.
(b)(ii) Figure 2.2 shows four types of chromosomal mutations K, L, M and N. Based on Figure 2.2, explain the mutation types of K, L, M and N.



Answer:
(a)
• Thumbprint pattern is an example of discontinuous variation.
• It is influenced by genetic factor.
• During gametogenesis / gamete formation, crossing over occurs during prophase I in meiosis
• Exchange of genetic material / DNA segment occurs at sister chromotids of homologous chromosome pair.
• It produces new genetic combination in gamete.
• During metaphase I in meiosis, independent assortment of chromosome takes place.
• Homologous chromosomes are arranged randomly in equatorial plane of cell during metaphase.
• Separation of homologous pair produces gametes with different genetic combinations.
• One haploid gamete fertilises at random with another haploid gamete.
• This will produce a diploid zygote with new combination of genes.

(b)(i)
• Gene mutation involves change in nucleotide base sequence in DNA molecule of a chromosome whereas chromosomal mutation involves change in structure and number of chromosomes.

• Types of gene mutation include deletion / insertion / substitution of base in a gene whereas types of chromosomal mutation include duplication / deletion/ inversion / translocation of a chromosome segment.

(b)(ii)
• Mutations of chromosomes K, L, M and N cause change in chromosomal structures.
• K is duplication.
• Part of the chromosome in gene A undergoes duplication.
• Mutant chromosome has two sets of gene A.
• L is deletion.
• Chromosome is cut between gene E and gene F, and F is lost.
• Mutant chromosome does not have gene F.
• M is inversion.
• The segment with D, E and F genes is cut, and the same segment is rejoined but in the opposite direction.
• N is translocation.
• Cutting of the chromosome between gene C and gene D; and another chromosome segment with genes X, Y and Z joins at gene C.


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