meiosis-I and meiosis-II to give rise to spermatids, which are
haploid (n = 23, in humans). So, when 'A' changes to 'B'
chromosome number is reduced to half.- Genetic disorder caused due to the presence of an
additional copy of X-chromosome resulting into a karyotype
of 44 + XXY is called Klinefelter's syndrome. Such an
individual has overall masculine development, however,
the feminine development (development of breast, i.e.,
Gynaecomastia) is also expressed. Such individuals are
sterile with undeveloped testes, mental retardation, female
like sparse body hair, knock knees, long limbs, feminine
pitched voice, etc. - (a) The given figure represents the structure of an antibody
molecule.
(b) IgA : It is the second most abundant class, constituting about
10 to 15 percent of antibodies of serum. It is mainly found in
sweat, tears, saliva, mucus, colostrum and gastrointestinal
secretions.
IgD : It is mainly found on the surface of B cells as antigen
receptors, where it activates B cells for antigen recognition.
It is about 0.2% of all antibodies in the blood.
IgE : It is less than 0.1% of all antibodies in the blood;
located on mast cells and basophils releasing histamine
from mast cells and basophils. It is involved in allergic
and hypersensitivity reactions; provides protection against
parasitic worms.
IgG :This is the most abundant class of Ig in the body
constituting approximately 80% of the total Igs. It protects
against bacteria and viruses by enhancing phagocytosis
and complement activation. It is found in the blood, lymph
and intestine.
IgM : IgM is about 5 to 10% of all antibodies in the blood.
It is also found in lymph. It activates the B cells. It is the
largest immunoglobulin and is the earliest to be synthesised
by foetus.
- (a) There are 64 triplet codons and only 20 amino acids.
Thus the incorporation of some amino acids must be
influenced by more than one codon. Only tryptophan (UGG)
and methionine (AUG) are specified by single codons. All
other amino acids are specified by two (e.g., phenylalanine
–UUU, UUC) to six (e.g., arginine—CGU, CGC, CGA, CGG,
AGA, AGG) codons. The latter are called degenerate or
redundant codons.
(b) RNA formed after transcription contains both introns
and exons and is called hnRNA. This hnRNA undergoes
processing such as splicing, capping and tailing to form
mRNA. Hence, hnRNA is the precursor of mRNA.
- Diagrammatic representation of regulation of gene
expression in lac operon of E.coli is as: - Exotic or alien species introduced inadvertently for their
economic and other uses become invasive and drive away
the local species. These species are considered to be second
major cause of extinction of species. Exotic species have
proved harmful to both aquatic and terrestrial ecosystems.
Island ecosystems are the most vulnerable due to small size
and small number of species. Examples: (i) Water hyacinth
(Eichhornia crassipes) was introduced in Indian waters to
reduce pollution. It has clogged water bodies including
wetlands at many places resulting in death of several
aquatic plants and animals. (ii) Nile perch (a predator fish)
was introduced in lake Victoria of South Africa. It killed and
eliminated ecologically unique assemblage of over 200
native species of small Cichlid fish.
OR
(a) Biofortification refers to breeding crops with higher levels of
vitamins, minerals, proteins and healthier fats.
Biofortification is undertaken with the objectives of
improving:
(i) Protein content and quality
(ii) Oil content and quality
(iii) Vitamin content and
(iv) Micronutrient and mineral content.
(b)
Crop Variety Resistance to diseases
Wheat Himgiri Leaf and stripe rust, hill
bunt
Brassica Pusa swarnim White rust
Cauliflower Pusa
shubhbraBlack rot and curl blight
black rot