Science (English Medium) Class 12 - CBSE Important Questions for Biology

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.

Describe the dihybrid cross upto F₂ generation as conducted by Gregor Mendel using pure lines of Garden Pea for characters-seed shape and seed colour.

Variations caused due to mutations are ______.

What should be the genotype of the indicated member?

Which one of the following is a stop codon?

(a) UAG

(b) UAC

(c) AUG

(d) UCA

Following are the features of genetic codes. What does each one indicate?
Stop codon; Unambiguous codon; Degenerate codon; Universal codon.

What do ‘Y’ and ‘B’ stand for in ‘YAC’ and ‘BAC’ used in the Human Genome Project (HGP)? Mention their role in the project.

Describe the process of transcription in bacteria

How do m-RNA, t-RNA and ribosomes help in the process of translation?

Explain the process of transcription in prokaryotes.

Name the enzyme and state its property that is responsible for continuous and discontinuous replication of the two strands of a DNA molecule

It is established that RNA is the first genetic material. Explain giving three reasons.

Name the enzyme responsible for the transcription of tRNA and the amino acid the initiator tRNA gets linked with.

State the aim and describe Messelson and Stahl’s experiment.

How are the following formed and involved in DNA packaging in a nucleus of a cell?

Differentiate between Euchromatin and Heterochromatin.