SPM Biology 2013


7 . Diagram 7.1 shows a pair of homologous chromosomes. A characteristic is determined by a pair of alleles. T and t represent the alleles for the characteristic of height.

Rajah 7.1 menunjukkan sepasang kromosom homolog. Suatu ciri ditentukan oleh sepasang alel. T dan t mewakili alel bagi ciri ketinggian.

(a) Based on Diagram 7.1, explain how the characteristic of height is determined.

Berdasarkan Rajah 7.1, terangkan bagaimana ciri ketinggian ditentukan.

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(b) Diagram 7.2 shows the inheritance of haemophilia in a family. Haemophilia is a sex-linked disease. The father is a normal male with genotype XHY, while the mother is a haemophiliac female with genotype XhXh. Explain the probability of the offsprings to inherit haemophilia.

Rajah 7.2 menunjukkan perwarisan hemofilia dalam sebuah keluarga. Hemofilia adalah penyakit terangkai seks. Bapanya seorang lelaki normal dengan genotip XHY, manakala ibunya seorang wanita hemofilia dengan genotip XhXh. Terangkan kebarangkalian anak-anak mewarisi hemofilia.

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(c) Diagram 7.3 shows the conditions of red blood cells of two individuals, P and Q. Individual Q suffers from a genetic disease. Explain the difference in health between individuals P and Q.

Rajah 7.3 menunjukkan keadaan sel darah merah dua individu, P dan Q. Individu Q menghidap suatu penyakit genetic. Terangkan perbezaan kesihatan antara individu P dengan individu Q.


(d) Bacteria can genetically modified to produce insulin. Explain the use of the insulin for a diabetic patient.

Bakteria boleh dibuah suai secara genetic untuk menghasilkan insulin. Terangkan kegunaan insulin itu bagi seorang pesakit kencing manis.Cher Questions Solution Bank Rumusan Jawapan SPM & IGCSE Questions Answers Solution


Answer ( 1 )


    7.a)-If T is a dominant allele for tall height and t is a recessive allele for short height.

    -An offspring inherits one allele from the father and one allele from the mother.

    -This can form a variation of genotypes, TT, Tt, tt depending on the genotypes of the parents and which allele the offspring inherited from their parents.

    -If the offspring is heterozygous (Tt), he will have a tall height due to the dominant allele which masks the effects of the recessive allele. So long as there is a dominant allele present, the offspring will have a tall height, if the offspring is homozygous recessive (tt) then he will have short height.


    b)please be aware that H/h is written as a superscript


    mother: X(h)X(h)


    “you may draw a genetic diagram for clarification”

    -father produces gametes X(H) and Y, mother produces gamete X(h).

    -one gamete from father fuses with one gamete from mother (fertilization).

    -possible offspring genotypes:

    X(H)X(h) or X(h)Y.


    1 X(H)X(h) : 1 X(h)Y

    1 normal daughter (hemophiliac carrier) : 1 hemophiliac son


    -All daughters would be normal, however they’re haemophiliac carriers as they inherit on normal copy from father X(H) and one faulty copy¬† X(h) from mother. They are heterozygous for haemophilia X(H)X(h). However they won’t be diseased as haemophilia is a recessive sex-linked disease.

    -All sons would be haemophiliac, as they inherit the Y chromosome from father and inherit the faulty copy from mother X(h). Since males only have one X chromosome this would mean that the sons will have haemophilia as they inherit X chromosome from mother who is homozygous recessive for the disease.


    c)Individual P has normal healthy red blood cells. Able to transport oxygen efficiently.

    Individual Q has sickled-cells.

    -Q produces defective haemoglobin which causes the transport of oxygen to be greatly reduced.

    -individual may be anaemic.

    -These sickle cells also like sticking together to from a clump, this can block capillaries and cause poor blood circulation.


    d)-Insulin is important to reduce blood glucose levels.

    -Some diabetic patients produce low levels of insulin.

    -Thus an insulin injection after a meal is very helpful for these individuals.

    -Reason being, insulin promotes the conversion of glucose into glycogen.

    -Thus blood glucose levels can then decrease back to the normal range.

    -In the presence of insulin, liver cells are also stimulated to convert excess glucose and store it in the form of glycogen. (helps to lower blood glucose levels as well).

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