Section E
Question 13: In order to trace the inheritance of traits Mendel crossed pea plants having one contrasting character or a pair of contrasting characters. When he crossed pea plants having round and yellow seeds with pea plants having wrinkled and green seeds, he observed that no plants with wrinkled and green seeds were obtained in the F1 generation. When the F1 generation pea plants were cross-bred by self-pollination, the F₂ generation had seeds with different combinations of shape and colour also.
(a) Write any two pairs of contrasting characteristics of the pea plant used by Mendel other than those mentioned above.
(b) Differentiate between dominant and recessive traits.
(c) State the ratio of the combinations observed in the seeds of F₂ generation (in the above case). What do you interpret from this result?
Answer:
(a) Seven pairs of contrasting characteristics of pea plants studied by Mendel in his experiments are as follows:-
I. Pea shape: Round or Wrinkled.
II. Pea color: Green or Yellow.
III. Pod shape: Constricted or Inflated.
IV. Pod color: Green or Yellow.
V. Flower color: Purple or White.
VI. Plant size: Tall or Dwarf.
VII. Position of flowers: Axial or Terminal.
(b) Difference Between Recessive and Dominant Traits
|
Chracteristics |
Dominant Trait |
Recessive Trait |
|---|---|---|
|
Features |
Even in cases when there is only one copy of the linked allele, dominant features are always shown. |
Only when both linked alleles are recessive can recessive features manifest. A dominant allele reduces the likelihood that the correlated trait will appear. |
|
Presentation |
Dominant allele is denoted by a capital letter |
Recessive allele is denoted by a small letter |
|
Traits |
|
|
(c) The ratio of combinations found in F₂ generation seeds is 9:3:3:1. Some of the F2 offspring in the cross seen above are tall plants with spherical seeds, while others are shorter plants with wrinkled seeds. A few F2 offspring had novel combinations. While some are small with spherical seeds, others are tall with wrinkled seeds. When variables governing seed color and shape recombine to generate zygotes that result in F2 offspring, new combinations of characteristics are formed in the F2 offspring. Consequently, the round seed/wrinkled seed trait and the tall/short trait are inherited separately.
OR
(c) Given below is a cross between a pure violet flowered pea plant (V) and a pure white flowered pea plant (v). Diagrammatically explain what type of progeny is obtained in F1, generation and F2, generation:
Pure violet flowered plant x Pure white flowered plant.
(VV) (vv)
Answer:
The cross is studied by monohybrid cross since it involves only one trait which is the flower color.
CBSE Previous Year Question Papers Class 10 Biology – 2023
CBSE Class 10 Previous Year Question Papers for Biology help you to understand the level of questions asked in the previous exams, along with the changes in pattern. Practicing class 10 PYQ enhances time-management skills while appearing in the board examination. CBSE 10th biology previous year’s paper makes you understand the importance of different topics that have been asked previously.
Solving previous year questions will boost your confidence level to appear in the examination with proper knowledge of different topics that will be asked. PYQ for class 10 enhances the understanding of the topic and acts as a checkpoint to see the level of preparation you have done.
Students are also advised to go through CBSE Class 10 Biology Sample Papers with answers on the official website of Geeks for Geeks for a better understanding of the exam pattern. You can find the CBSE class 10 biology previous year question paper with solutions pdf for free download here.
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