SPM Biology 2018

Question

5. Diagram 5.1 shows the cross of a round and yellow seed pea plant with wrinkled and green seed pea plant. All of the offsprings in the F1 generation produced are round and yellow seeds.

Rajah 5.1 menunjukkan kacukan antara pokok kacang pea berbiji bulat dan kuning dengan pokok kacang pea berbiji kedut dan hijau. Semua anak generasi F1 yang terhasil adalah berbiji bulat dan kuning.

(a) State the recessive traits of the pea plant. Explain your answer.

Nyatakan trait resesif pokok kacang pea itu. Terangkan jawapan anda.

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(b) One of the offsprings in F1 generation in Diagram 5.1 is labelled as J. J is crossed with pea plant K with genotype RRyy.

Satu daripada anak generasi F1 dalam Rajah 5.1 dilabelkan sebagai J. J dikacukan dengan pokok kacang pea K bergenotip RRyy.

(i) Complete the schematic genetic diagram in Diagram 5.2.

Lengkapkan rajah skema pewarisan dalam Rajah 5.2.

(ii) Explain how offspring L inherits the round and yellow seed traits.

Terangkan bagaimana anak L mewarisi trait berbiji bulat dan kuning.

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(c) Diagram 5.2 shows another example of a genetic cross. State the differences between this genetic cross in Diagram 5.3 with the cross shown in Diagram 5.1.

Rajah 5.4 menunjukkan satu contoh lain bagi kacukan pewarisan. Nyatakan perbezaan antara kacukan perwarisan dalam Rajah 5.3 dengan kacukan yang ditunjukkan dalam Rajah 5.1.

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(d) The following are the phenotype and the genotype of pea plant X. Pea plant X is crossed with pea plant Y. Identify the genotype of pea plant Y so that the cross will produce all offsprings with the phenotype of tall tree and white flower. Explain your answer.

Berikut adalah fenotip dan genotip pokok kacang pea X. Pokok kacang pea X dikacukkan dengan pokok kacang pea Y. Kenal pasti genotip pokok kacang pea Y supaya kacukan tersebut akan menghasilkan semua anak yang mempunyai fenotip pokok tinggi dan bunga putih. Terangkan jawapan anda

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Answer ( 1 )

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    2020-12-29T19:05:46+08:00

    5. a) The recessive traits of the pea plant are wrinkled and green seed. This is because the F1 generation has resulted in all round and yellow seeds which is the dominant trait that has masked the effect of the recessive allele (wrinkled , green). Only one dominant allele is needed to mask the effect of the recessive allele.

     

    b) i) Genotype : RrYy

    Gamete: Ry

    Offsprings: RrYy, Rryy

    ii) Offspring L has inherited two dominant alleles (R) from its parents which gave rise to the round seed trait. Next, offspring L inherited one dominant allele (Y) for yellow colour and one recessive allele (y) for green colour, since the dominant allele masks the effects of the recessive allele, this results in the offspring having the phenotype of yellow colour.

     

    c)

    Diagram 5.1 Diagram 5.3 
    This is a dihybrid cross which involves two pairs of alleles that determines two characteristics (shape and colour of seed)

    F2 phenotypic ratio will be 9:3:3:1

    This is a monohybrid cross which involves only one pair of alleles that determines one characteristic (height) 

    F2 phenotypic ratio will be 3:1

     

    d) The genotype of pea plant Y would be TTww.  The white flower trait is recessive as seen with the genotype of X (ww), thus in order to ensure that all offspring would have white flowers, Y has to have two recessive alleles (ww) as well. Next, the dominant allele (T) results in the tall trait whereas the recessive allele (t) would result in the short trait. So to ensure that all offspring would have the tall trait, Y needs to have two dominant alleles (TT). If Y has any recessive allele (t), it might cause the offspring to have the short trait instead because X is heterozygous (Tt) for tallness, during the cross the offspring might inherit one recessive allele (t) each from X and Y, resulting in (tt)- short trait.

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