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As in many Citrus and Mango varieties some of the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into the embryos. In such species each ovule contains many embryos. Occurrence of more than one embryo in a seed is referred as polyembryony. If hybrids are made into apomicts, there is no segregation of characters in the hybrid progeny. Then the farmers can keep on using the hybrid seeds to raise new crop year after year and he does not have to buy hybrid seeds every year.

The zygote needs nourishment during its development. As the mature, fertilised embryo sac offers very little nourishment to the zygote, the PEC divides and generates the endosperm tissue which nourishes the zygote. Hence, the zygote always divides after division of PEC.

Yes, they are different. Parthenocarpy leads to development of seedless fruits.
Apomixis leads to embryo development.

Thalamus become fruit, ovary becomes fruit, fruit formation without fertilisation, produce seeds without fertilization,more than one seed in a seed.

1. Fertilization is fusion of male and female gametes. 

2. Pollination is transfer of pollen grains which carry non-motile male gametes. 

3. Pollen grains are transferred from anther to stigma of flower where they germinate. 

4. Both male and female gametes are nonmotile and they are produced at two different sites.

5. Therefore the pollination process is necessary for act of fertilization in plants.

Apomixis is a type of asexual reproduction that mimics sexual reproduction to form seeds without fertilisation. 

In apomictic seeds, parental characters are maintained in the progeny/offspring as there is no meiosis or segregation of characters. 

If desired hybrid seeds are made apomictics the farmers can keep on using the hybrid seeds to raise new crops year after year. 

No, they are not necessary. Apomixis is actually an alternative to sexual reproduction, although the female sexual apparatus is used in the process. In apomicts, embryos can develop directly from the nucellus or synergid or egg. Therefore, there is no need for either pollination or fertilisation.

Apomixis is formation of embryos without formation of gametes hence there is no need of pollination and fertilization.

Packaging of chromatin

Histones are positively charged basic proteins. The negatively charged DNA is wrapped around the positively charged histone octamer to form nucleosome.

Distance between two base pairs = 0.34 mm or 0.34×10^–6 mm Number of base pairs in 1.36 mm DNA segment

= \(\frac{1}{0.34\times10^6}\) x 1.36

= 4 x 10⁶ bp

Correct answer is (d) sigma factor

Match the following:

(c) micropylar region

Yes, if embryo develops from the cells of nucellus or integuments, it will be diploid.

It is the transfer of pollen grains to the stigma of a pistil.

(C) 1 : 2 : 1

1 : 2 : 1; one homozygous dominant, two heterozygous dominant and one homozygous recessive.

i. Write the base sequence of the RNA got after transcription of the given sequence. 

ii. What is the distance maintained between the two consecutive pairs of bases in the DNA molecule? 

iii. Who contributed the base complementary rule?

(a) GTA ATC ATG CTG
(b) GUA AUCAUGCUG.

(i) TACAGATAT 

(ii) UACAGAUAU

(iii)

Correct answer is (d) complementary strand

After syngamy and triple fusion in embryosac, embryo will be diploid and endosperm will be Triploid.

Polarity of DNA strand a-b is 3'--> 5' & c-d has polarity 5'--> 3'.

S-phase. 

Polyploidy

Detailed answer:

DNA replication takes place in S-phase (Synthetic phase) of cell cycle in eukaryotes. If this replication of DNA is not followed by cell division the DNA contents of the cell will get doubled i.e., duplicate set of DNA will be formed. This will result in autopolyploidy. 

Correct answer is

(A) phenotypic ratio obtained in F₂ generation of monohybrid cross.

Correct answer is

(B) 3:1

i) TACAGATAT 

ii) UACAGAUAU 

iii) Hydrogen bonds

a- Leading strand (continuous) 

b-Lagging strand (discontinuous).

The DNA-dependent DNA polymerase catalyses polymerisation only in one direction i.e., 5′→3′. Therefore, in one strand with polarity 3′→5′ continuous replication takes place whereas the other strand with polarity 5′→3′ carries out discontinuous replication. 

The strand with polarity 3′→5′ is called leading strand and the strand with polarity 5′→3′ is called lagging strand.

There is a definite region in DNA where the replication originates called as origin of replication, For long DNA molecules since the two strands of DNA cannot be separated in its entire length, the replication occurs within a small opening of the DNA helix, referred to as replication fork. The DNA dependent DNA polymerase, catalyze polymerization only in one direction, that is 5' ---> 3', on one strand (the template with polarity 3' ---> 5') the replication is continuous, while on the other (the template with polarity 5' ---> 3;) it is discontinuous. The discontinuous synthesized fragments are later joined by the enzyme DNA ligase.

a) If both the strands act as template, they would code for RNA molecule with different sequences, and in turn they code for different proteins. 

b) the two RNA molecules if produced simultaneously would be complementary to each other , hence would for a double stranded RNA.

(i) In long DNA molecules, since the two strands of DNA cannot be separated in its entire length, the replication occur within a small opening to the DNA helix, referred to as a replication fork. 

(ii) The DNA-dependent DNA polymerases catalyse polymerization of the nucleotides only in 5' ---> 3' direction. 

Consequently, on one of the template strands (with 3' --> 5' polarity) the synthesis of DNA is continuous, . while on the other template strand (with polarity 5' ---> 3'), the synthesis of DNA is discontinuous, i.e., short stretches of DNA are synthesized. 

(iii) The discontinuously synthesized strands are later joined together by the enzyme DNA ligase.

It not only catalyses the polymerization reaction fast but also catalyses the reaction accurately.

(a) A-Template strand = 1 

B-Coding strand: 1 

Template strand has polarity 3'-5' 

Coding strand has polarity 5'-3' 

On the basis of polarity with respect to promoter.

(b) In initiation sigma factor associates with RNA polymerase to initiate transcription, Rho factor gets associated to RNA polymerase to terminate transcription.

(c) RNA polymerase I - Transcribes -RNAs 

RNA polymerase III - Transcribes tRNA / 5srRNA / 5nRNA.

(i) mRNA-(Messenger RNA) : decides the sequence of amino acids. 

(ii) tRNA-(Transfer RNA) : 

(a) Recognises the codon on mRNA 

(b) transport the aminoacid to the site of protein synthesis. 

(iii) rRNA (Ribosomal RNA) : Plays the structural and catalytic role during translation.

Genetic code is the relationship between the sequence of nucleotides on mRNA and sequence of amino acids in the polypeptide.
Its features are

• The genetic code is universal ie., the codons code for one amino acid is same in all organism.
• Codons are triplet codons and there are 64 codons. 61 codons code for twenty different amino acids while the other three (UAA, UAG, UGA) are termination codons which do not code for any amino acids.
• Each codon codes for only one particular amino acid. Therefore it is unambiguous.
• Some amino acids are coded by more than one codon there for it is said to be degenerate.
• The codons are read in a continuous manner, without any punctuation ie., codons are comma less.
• AUG has dual functions of coding for metheonine as well as functioning as initiation codon.

Sigma factor.

Correct option (C) The frequencies of some alleles in a population's gene pool must change over successive generations.   

Explanation:

Evolution may be described as the change in heritable characteristics of a population over successive generation. So, for evolution to occur, allele frequency must change for whole group of population over successive generation.

The RNAs are of 3 types

• Messenger RNA (m – RNA)
• Transfer RNA (t – RNA)
• Ribosomal RNA (r – RNA)

m – RNA It provides the template for polypeptide synthesis, ie., it decides the sequence of amino acids in the polypeptide through the sequence of bases on it. t – RNA It has the shape of clover leaf in two dimensional structure It transports the amino acids to the site of protein synthesis it recognises the codon on m RNA. r – RNA It plays the structural and catalytic role during translation.

i. Role of polymerase in transcription in bacteria 

a. Initiation: σ (sigma) factor recognises the start signal and promotor region on DNA and the σ (sigma) with RNA polymerase binds to the promoter and initiates transcription. 

b. Elongation: The RNA polymerase after initiation of RNA transcription loses the σ-factor but continues the process of RNA formation. 

c. Termination: Once the RNA polymerase reaches the termination region of DNA, the RNA polymerase is separated from DNA-RNA hybrid, as a result nascent RNA separates. This process is called termination which is facilitated by certain termination factor . 

Role of polymerase in transcription in eukaryotes 

a. In eukaryotes, apart from the RNA polymerase found in the organelles, three types of RNA polymerases are found in the nucleus. 

b. RNA polymerase II transcribes the precursor of mRNA (called as heterogeneous nuclear RNA (hnRNA). 

c. RNA polymerase III helps in transcription of tRNA, 5S rRNA, and snRNAs (small nuclear RNAs). 

ii. Francis Crick postulated the role of an adaptor. tRNA or transfer RNA is the adaptor molecule.

The Correct option is (A)

1. In bacteria, m-RNA provides the encoded message for protein synthesis; t-RNA brings specific amino acid to the site of translation; r-RNA plays role in providing binding site to m-RNA and tRNA.

2. There is single DNA dependent-RNA polymerase that catalyses transcription of all 3 types of RNA in bacteria. 

3. RNA polymerase binds to promoter and initiates transcription (initiation) and synthesizes RNA.

Elongation process of Transcription in bacteria

-After binding to the promoter, the RNA polymerase facilitates the opening of the DNA.-It uses nucleoside triphosphates as substrate and polymerises the nucleotides in a templatdependent fashion following complementarity of bases in 5' → 3 direction The process continues till the RNA polymerase reaches the terminator region on the DNA stran.

In eukaryotes, the hnRNA (primary transcript of mRNA) has coding sequences, 2 called exons as well as non-coding sequences, called introns, i.e., the information is split- If undergoes a process, called splicing, in which the introns are remove and the exons are joined together in a particular manner, to form the functional mRNA.- In prokaryotes, the mRNA is polycistronic, i.e., codes for more than one polypeptide.- The information is continuous and no splicing is required.

Both DNA and RNA are able to mutate. In fact, RNA being unstable, mutate at a faster rate. Consequently, viruses having RNA genome and having shorter life span mutate and evolve faster.