- Klinefelter's syndrome is caused due to trisomy of X
chromosome. Klinefelter’s syndrome (XXY) is caused by
presence of extra X-chromosome due to union of non-
disjunct XX egg and a normal Y sperm or normal X egg and
abnormal XY sperm. The individual has 2n = 47 chromosomes
(44 + XXY) instead of 46. These individuals are genetically
sterile males have underdeveloped testes, azospermia (less
and deformed sperm), gynaecomastia (enlarged breast),
mental retardation, occurrence of barr body etc. - (a) Cro-Magnon man was first discovered in 1868 from
Cro-Magnon rocks of France.
(b) Cro-Magnon had cranial capacity of about 1650 cc.
(c) Two important characteristics of Cro-Magnon are:
(i) They could walk and run faster.
(ii) The made excellent tools and ornaments using stones,
bones, elephant tusks etc.
- (a) Mesozoic era
(b) Carboniferous period
(c) Coenozoic era - The salient features of Human Genome Project are as
follows:
(i) The human genome contains 3164.7 million
nucleotides base pairs.
(ii) The size of the genes varies, an average gene consists
of 3000 base pairs while the largest gene, dystrophin
consists of 2.4 million base pairs.
(iii) The total number of genes is estimated about 25,000
and 99.9% of the nucleotides are the similar in all
humans. The size of genome or number of genes is
not connected with complexity of body organisation.
Only 0.1% of human genome with about 3.2 million
nucleotides represent variability.
(iv) The functions of over 50% of the discovered genes are
not known.
(v) Only less than 2% of the genome codes for structural
proteins.
(vi) Repetitive sequences (10-1000 times) make up a large
portion of the human genome.
(vii) Repetitive sequences throw light on chromosome
structure, dynamics and evolution, though they are
thought to have no direct coding functions.
(viii) Chromosome 1 has 2968 genes (the maximum) and
the Y-chromosome has 231 genes (the least).
(ix) Scientists have identified about 1.4 million locations,
where DNA differs in single base in human beings,
these are called single nucleotide polymorphisms
(SNPs, pronounced as ‘snips’).
(x) It has applications in study of various disorders
with genetic basis like endocrine diseases, cancers,
neurological, cardiovascular, inborn metabolic
errors, etc.
OR
Mendelian disorders: Phenylketonuria, Tay-Sach's disease
Alzheimer's disease, Huntington's disease.
Chromosomal disorders: Myelogenous Leukemia, Cri-du-
chat syndrome.- (a)
(b) The promoter gene is located towards 5′-end of the
structural gene of coding strand. It is a DNA sequence that
provides binding site for RNA polymerase. It is the presence
of a promoter in a transcription unit that also defines the
template and coding strands.- In humans, sex of the child is determined at the time of
fertilisation. The female parent produces only one type of
gamete with X-chromosome while the male gametes are
of two types, one with X-chromosome and other with
Y-chromosome. Fertilisation of the egg with sperm carrying
X-chromosome produces a female child while fertilisation
with sperm carrying Y-chromosome gives rise to male child.
Thus, sex of the child is determined by the father and not by
the mother. - (a) Theory of Spontaneous Generation states that life
originated from non-living things such as decaying and
rotting matter like straw, mud, etc. in a spontaneous manner.
Van Helmont believed that human sweat and wheat grains
could give rise to organism.
(b) This theory was disproved by Francesco Redi, Lazzaro
Spallanzani and Louis Pasteur. - (a) Sickle-cell anaemia is an autosomal recessive disorder.
When two heterozygous individual marry (carrier for sickle cell
anaemia), they produce a child suffering from the disorder. In
this disorder the erythrocytes become sickle shaped under
oxygen deficiency states, such as during strenuous exercise
and at high altitudes. It is caused by the formation of an
abnormal haemoglobin called haemoglobin –S.
In sickle-cell anaemia, haemoglobin-S differs from normal
haemoglobin-A in only one amino acid— 6th amino acid
of β-chain, (glutamic acid is replaced by valine) due to
substitution (transversion) of T by A in the second position
of the triplet codon CTC which is changed to CAC in the
β-haemoglobin gene situated on chromosome 11.
During conditions of oxygen deficiency 6-valine forms
hydrophobic bonds with complementary sites of other
globin molecules. It distorts their configuration. As a result,
erythrocytes having haemoglobin-S become sickle-shaped.
The cells cannot pass through narrow capillaries. They have