Class 12th Biology 2012 Set1 Outside Delhi Board Paper Solution
Question 30
Describe Frederick Griffiths experiment on Streptococcus pneumonia. Discuss the conclusion he arrived at.
Describe Frederick Griffiths experiment on Streptococcus pneumonia. Discuss the conclusion he arrived at.
OR
(a) Explain a monohybrid cross taking seed coat colour as a trait in Pisum sativum. Work out the cross upto F₂ generation.
(b) State the laws of inheritance that can be derived from such a cross.
(c) How is the phenotypic ratio of F₂ generation different in a dihybrid cross?
Answer
Frederick Griffith performed experiments on Streptococcus pneumonia which is responsible for causing pneumonia and mice. He observed that the bacteria produce two colonies:
(i) R strain: or rough colonies which are non-virulent.
(ii) S strain: or smooth colonies which are virulent and caused death of mice.
He observed that S cells are virulent due to production of a smooth polysaccharide coat which is absent in R- cells. He performed the following experiment:
Mice + R-cell bacteria ----> Mice lived
Mice + S- cell bacteria ------> Mice died
Then he killed S- celled bacteria by heating which cause denaturation of its genetic material and then injected in mice.
Mice + Heat killed S- cells ------> Mice lived
Now he injected mice with heat killed S- cells and non-virulent R- cells.
Mice + Heat killed S- cells + R-cells ----->Mice died.
Then he recovered living S-cells from the dead mice.
Then he concluded that some transforming principle had been transferred from heat killed S- cell to living R- cells which enables R- cells to secrete polysaccharide coat and become virulent.
OR
(a)
(b)The law of inheritance is the law of segregation which is based on the fact that the alleles do not show any blending and that both the characters are recovered as such in the F₂ generation.
(c)The phenotypic ratio of F₂ generation in a monohybrid cross is 1:2:1 whereas the ratios of F₂ generation in a dihybrid cross is 9:3:3:1.
Popular Questions of Class 12th biology
- Q:- What is spermatogenesis? Briefly describe the process of spermatogenesis.
- Q:- Why is reproduction essential for organisms? Answer
- Q:- Write a short note on
(a) Adaptations of desert plants and animals
(b) Adaptations of plants to water scarcity
(c) Behavioural adaptations in animals
(d) Importance of light to plants
(e) Effect of temperature or water scarcity and the adaptations of animals. - Q:- With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
- Q:- What is DNA fingerprinting? Mention its application.
- Q:- What is oogenesis? Give a brief account of oogenesis.
- Q:- Describe the structure of a seminiferous tubule.
- Q:- What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
- Q:- With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.
- Q:- Explain the Law of Dominance using a monohybrid cross.
Recently Viewed Questions of Class 12th biology
- Q:- What are the major functions of male accessory ducts and glands?
- Q:- What do you think is the significance of reproductive health in a society?
- Q:- Distinguish between
(a) Grazing food chain and detritus food chain
(b) Production and decomposition
(c) Upright and inverted pyramid
(d) Food chain and Food web
(e) Litter and detritus
(f) Primary and secondary productivity - Q:- Draw a well-labelled diagram of an antibody molecule.
- Q:- In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?
- Q:-
Explain the following terms with example
(a) Co-dominance
(b) Incomplete dominance - Q:- Find out the role of microbes in the following and discuss it with your teacher.
(a) Single cell protein (SCP)
(b) Soil - Q:- Why is the offspring formed by asexual reproduction referred to as clone?
- Q:- Mention any two autosomal genetic disorders with their symptoms.
- Q:- The second trophic level in a lake is-
(a) Phytoplankton
(b) Zooplankton
(c) Benthos
(d) Fishes