Science (English Medium) इयत्ता १२ - CBSE Important Questions

Name the pollutant attributed to be the cause of ‘ozone-hole’ over the Antarctica region.

List the greenhouse gases other than carbon dioxide.

What is heterogamety ? Explain the mechanism of sex determinatin in Drosophila.

How would you find out whether a given tall garden pea plant is homozygous or heterzygous? Substantiate your answer with the help fo Punnett squares.

Given below are the F₂ – phenotypic ratios of two independently carried monohybrid crosses :
(i) 1 : 2 : 1
(ii) 3 : 1
Mention what does each ratio suggest.

Answer the following question.
Name the layer of the atmosphere that is associated with ‘good ozone’.

Answer the following question.
Write the basis on which Alfred Sturtevant explained gene mapping.

Answer the following question.
Name the layer of the atmosphere that is associated with 'good ozone'.

Answer the following question.
Compare in any three ways the chromosomal theory of inheritance as proposed by Sutton and Bovery with that of experimental results on pea plant presented by Mendel.

An electrostatic precipitator in a thermal power plant is not able to generate a high voltage of several thousand. Write the ecological implication because of it.

Answer the following question.
List four benefits to human life by eliminating the use of CFC_s.

Justify the need for the signing of the 'Montreal Protocol' by the participating nations in 1987.

Answer the following question.
Two children, A and B aged 4 and 5 years respectively visited a hospital with a similar genetic disorder. The girl A was provided enzyme-replacement therapy and was advised to revisit periodically for further treatment. The girl, B was, however, given a therapy that did not require revisit for further treatment.

Why did the treatment provided to girl A required repeated visits?

Answer the following question.
Two children, A and B aged 4 and 5 years respectively visited a hospital with a similar genetic disorder. The girl A was provided enzyme-replacement therapy and was advised to revisit periodically for further treatment. The girl, B was, however, given a therapy that did not require revisit for further treatment.

How was the girl B cured permanently?

Albinism is known to be due to an autosomal recessive mutation. The first child of a couple with normal skin pigmentation was an albino. What is the probability that their second child will also be an albino?

Water samples were collected at points A, B and C in a segment of a river near a sugar factory and tested for BOD level. The BOD levels of samples A, B and C were 400 mg/L, 480 mg/L and 8 mg/L respectively. What is this indicative of? Explain why the BOD level gets reduced considerably at the collection point C?

Assertion: When white eyed, yellow bodied Drosophila females were hybridized with red eyed, brown-bodied males; and F₁ progeny was intercrossed, F₂ ratio deviated from 9 : 3 : 3 : 1.

Reason: When two genes in a dihybrid are on the same chromosome, the proportion of parental gene combinations is much higher than the non-parental type.

A true breeding pea plant, homozygous dominant for inflated green pods is crossed with another pea plant with constricted yellow pods (ffgg). With the help of Punnett square show the above cross and mention the results obtained phenotypically and genotypically in F₁ generation.

Study the Pedigree chart given below and answer the questions that follow:

Symbols used in the given Pedigree Chart are as follows:

	Carrier male
	Affected male
	Normal male
	Carrier female
	Affected female
	Normal female

(a) On the basis of the inheritance pattern exhibited in this pedigree chart, what conclusion can you draw about the pattern of inheritance?

(b) If the female is homozygous for the affected trait in this pedigree chart, then what percentage of her sons will be affected?

(c) Give the genotype of offspring 1, 2, 3 and 4 in III generations.

OR

(c) In this type of inheritance pattern, out of male and female children which one has less probability of receiving the trait from the parents? Give a reason.

"It is sometimes observed that the F₁ progeny shows a phenotype that resembles both the parents." Explain this type of inheritance using the example of A, B, and O blood groups in human.